path: root/mysys/mf_pagecache.c

/* Copyright (C) 2000-2006 MySQL AB

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA */

/*
  These functions handle page cacheing for Maria tables.

  One cache can handle many files.
  It must contain buffers of the same blocksize.
  init_pagecache() should be used to init cache handler.

  The free list (free_block_list) is a stack like structure.
  When a block is freed by free_block(), it is pushed onto the stack.
  When a new block is required it is first tried to pop one from the stack.
  If the stack is empty, it is tried to get a never-used block from the pool.
  If this is empty too, then a block is taken from the LRU ring, flushing it
  to disk, if necessary. This is handled in find_key_block().
  With the new free list, the blocks can have three temperatures:
  hot, warm and cold (which is free). This is remembered in the block header
  by the enum BLOCK_TEMPERATURE temperature variable. Remembering the
  temperature is necessary to correctly count the number of warm blocks,
  which is required to decide when blocks are allowed to become hot. Whenever
  a block is inserted to another (sub-)chain, we take the old and new
  temperature into account to decide if we got one more or less warm block.
  blocks_unused is the sum of never used blocks in the pool and of currently
  free blocks. blocks_used is the number of blocks fetched from the pool and
  as such gives the maximum number of in-use blocks at any time.
*/

#include "mysys_priv.h"
#include <pagecache.h>
#include "my_static.h"
#include <m_string.h>
#include <errno.h>
#include <stdarg.h>
#include <my_bit.h>


/*
  Some compilation flags have been added specifically for this module
  to control the following:
  - not to let a thread to yield the control when reading directly
    from page cache, which might improve performance in many cases;
    to enable this add:
    #define SERIALIZED_READ_FROM_CACHE
  - to set an upper bound for number of threads simultaneously
    using the page cache; this setting helps to determine an optimal
    size for hash table and improve performance when the number of
    blocks in the page cache much less than the number of threads
    accessing it;
    to set this number equal to <N> add
      #define MAX_THREADS <N>
  - to substitute calls of pthread_cond_wait for calls of
    pthread_cond_timedwait (wait with timeout set up);
    this setting should be used only when you want to trap a deadlock
    situation, which theoretically should not happen;
    to set timeout equal to <T> seconds add
      #define PAGECACHE_TIMEOUT <T>
  - to enable the module traps and to send debug information from
    page cache module to a special debug log add:
      #define PAGECACHE_DEBUG
    the name of this debug log file <LOG NAME> can be set through:
      #define PAGECACHE_DEBUG_LOG  <LOG NAME>
    if the name is not defined, it's set by default;
    if the PAGECACHE_DEBUG flag is not set up and we are in a debug
    mode, i.e. when ! defined(DBUG_OFF), the debug information from the
    module is sent to the regular debug log.

  Example of the settings:
    #define SERIALIZED_READ_FROM_CACHE
    #define MAX_THREADS   100
    #define PAGECACHE_TIMEOUT  1
    #define PAGECACHE_DEBUG
    #define PAGECACHE_DEBUG_LOG  "my_pagecache_debug.log"
*/

#define PAGECACHE_DEBUG_LOG  "my_pagecache_debug.log"

/*
  In key cache we have external raw locking here we use
  SERIALIZED_READ_FROM_CACHE to avoid problem of reading
  not consistent data from te page
*/
#define SERIALIZED_READ_FROM_CACHE yes

#define BLOCK_INFO(B) \
  DBUG_PRINT("info", \
             ("block 0x%lx, file %lu, page %lu, s %0x, hshL 0x%lx, req %u/%u", \
              (ulong)(B), \
              (ulong)((B)->hash_link ? \
                      (B)->hash_link->file.file : \
                      0), \
              (ulong)((B)->hash_link ? \
                      (B)->hash_link->pageno : \
                      0), \
              (B)->status, \
              (ulong)(B)->hash_link, \
              (uint) (B)->requests, \
              (uint)((B)->hash_link ? \
                     (B)->hash_link->requests : \
                       0)))

/* TODO: put it to my_static.c */
my_bool my_disable_flush_pagecache_blocks= 0;

#if defined(MSDOS) && !defined(M_IC80386)
/* we nead much memory */
#undef my_malloc_lock
#undef my_free_lock
#define my_malloc_lock(A,B)  halloc((long) (A/IO_SIZE),IO_SIZE)
#define my_free_lock(A,B)    hfree(A)
#endif /* defined(MSDOS) && !defined(M_IC80386) */

#define STRUCT_PTR(TYPE, MEMBER, a)                                           \
          (TYPE *) ((char *) (a) - offsetof(TYPE, MEMBER))

/* types of condition variables */
#define  COND_FOR_REQUESTED 0  /* queue of thread waiting for read operation */
#define  COND_FOR_SAVED     1  /* queue of thread waiting for flush */
#define  COND_FOR_WRLOCK    2  /* queue of write lock */
#define  COND_SIZE          3  /* number of COND_* queues */

typedef pthread_cond_t KEYCACHE_CONDVAR;

/* descriptor of the page in the page cache block buffer */
struct st_pagecache_page
{
  PAGECACHE_FILE file;    /* file to which the page belongs to  */
  maria_page_no_t pageno; /* number of the page in the file   */
};

/* element in the chain of a hash table bucket */
struct st_pagecache_hash_link
{
  struct st_pagecache_hash_link
    *next, **prev;                   /* to connect links in the same bucket  */
  struct st_pagecache_block_link
    *block;                          /* reference to the block for the page: */
  PAGECACHE_FILE file;               /* from such a file                     */
  maria_page_no_t pageno;            /* this page                            */
  uint requests;                     /* number of requests for the page      */
};

/* simple states of a block */
#define BLOCK_ERROR       1 /* an error occurred when performing disk i/o  */
#define BLOCK_READ        2 /* the is page in the block buffer             */
#define BLOCK_IN_SWITCH   4 /* block is preparing to read new page         */
#define BLOCK_REASSIGNED  8 /* block does not accept requests for old page */
#define BLOCK_IN_FLUSH   16 /* block is in flush operation                 */
#define BLOCK_CHANGED    32 /* block buffer contains a dirty page          */
#define BLOCK_WRLOCK     64 /* write locked block                          */

/* page status, returned by find_key_block */
#define PAGE_READ               0
#define PAGE_TO_BE_READ         1
#define PAGE_WAIT_TO_BE_READ    2

/* block temperature determines in which (sub-)chain the block currently is */
enum BLOCK_TEMPERATURE { BLOCK_COLD /*free*/ , BLOCK_WARM , BLOCK_HOT };

/* debug info */
#ifndef DBUG_OFF
static char *page_cache_page_type_str[]=
{
  (char*)"PLAIN",
  (char*)"LSN"
};
static char *page_cache_page_write_mode_str[]=
{
  (char*)"DELAY",
  (char*)"NOW",
  (char*)"DONE"
};
static char *page_cache_page_lock_str[]=
{
  (char*)"free  -> free ",
  (char*)"read  -> read ",
  (char*)"write -> write",
  (char*)"free  -> read ",
  (char*)"free  -> write",
  (char*)"read  -> free ",
  (char*)"write -> free ",
  (char*)"write -> read "
};
static char *page_cache_page_pin_str[]=
{
  (char*)"pinned   -> pinned  ",
  (char*)"unpinned -> unpinned",
  (char*)"unpinned -> pinned  ",
  (char*)"pinned   -> unpinned"
};
#endif
#ifdef PAGECACHE_DEBUG
typedef struct st_pagecache_pin_info
{
  struct st_pagecache_pin_info *next, **prev;
  struct st_my_thread_var *thread;
}  PAGECACHE_PIN_INFO;
/*
  st_pagecache_lock_info structure should be kept in next, prev, thread part
  compatible with st_pagecache_pin_info to be compatible in functions.
*/
typedef struct st_pagecache_lock_info
{
  struct st_pagecache_lock_info *next, **prev;
  struct st_my_thread_var *thread;
  my_bool write_lock;
} PAGECACHE_LOCK_INFO;


/* service functions maintain debugging info about pin & lock */


/*
  Links information about thread pinned/locked the block to the list

  SYNOPSIS
    info_link()
    list                 the list to link in
    node                 the node which should be linked
*/

void info_link(PAGECACHE_PIN_INFO **list, PAGECACHE_PIN_INFO *node)
{
  if ((node->next= *list))
    node->next->prev= &(node->next);
  *list= node;
  node->prev= list;
}


/*
  Unlinks information about thread pinned/locked the block from the list

  SYNOPSIS
    info_unlink()
    node                 the node which should be unlinked
*/

void info_unlink(PAGECACHE_PIN_INFO *node)
{
  if ((*node->prev= node->next))
   node->next->prev= node->prev;
}


/*
  Finds information about given thread in the list of threads which
  pinned/locked this block.

  SYNOPSIS
    info_find()
    list                 the list where to find the thread
    thread               thread ID (reference to the st_my_thread_var
                         of the thread)

  RETURN
    0 - the thread was not found
    pointer to the information node of the thread in the list
*/

PAGECACHE_PIN_INFO *info_find(PAGECACHE_PIN_INFO *list,
                              struct st_my_thread_var *thread)
{
  register PAGECACHE_PIN_INFO *i= list;
  for(; i != 0; i= i->next)
    if (i->thread == thread)
      return i;
  return 0;
}
#endif

/* page cache block */
struct st_pagecache_block_link
{
  struct st_pagecache_block_link
    *next_used, **prev_used;   /* to connect links in the LRU chain (ring)   */
  struct st_pagecache_block_link
    *next_changed, **prev_changed; /* for lists of file dirty/clean blocks   */
  struct st_pagecache_hash_link
    *hash_link;           /* backward ptr to referring hash_link             */
  PAGECACHE_WQUEUE
    wqueue[COND_SIZE];    /* queues on waiting requests for new/old pages    */
  uint requests;          /* number of requests for the block                */
  byte *buffer;           /* buffer for the block page                       */
  uint status;            /* state of the block                              */
  uint pins;              /* pin counter                                     */
#ifdef PAGECACHE_DEBUG
  PAGECACHE_PIN_INFO *pin_list;
  PAGECACHE_LOCK_INFO *lock_list;
#endif
  enum BLOCK_TEMPERATURE temperature; /* block temperature: cold, warm, hot  */
  enum pagecache_page_type type; /* type of the block                        */
  uint hits_left;         /* number of hits left until promotion             */
  ulonglong last_hit_time; /* timestamp of the last hit                      */
  KEYCACHE_CONDVAR *condvar; /* condition variable for 'no readers' event    */
};

#ifdef PAGECACHE_DEBUG
/* debug checks */
my_bool info_check_pin(PAGECACHE_BLOCK_LINK *block,
                       enum pagecache_page_pin mode)
{
  struct st_my_thread_var *thread= my_thread_var;
  DBUG_ENTER("info_check_pin");
  PAGECACHE_PIN_INFO *info= info_find(block->pin_list, thread);
  if (info)
  {
    if (mode == PAGECACHE_PIN_LEFT_UNPINNED)
    {
      DBUG_PRINT("info",
                 ("info_check_pin: thread: 0x%lx block 0x%lx: LEFT_UNPINNED!!!",
                  (ulong)thread, (ulong)block));
      DBUG_RETURN(1);
    }
    else if (mode == PAGECACHE_PIN)
    {
      DBUG_PRINT("info",
                 ("info_check_pin: thread: 0x%lx block 0x%lx: PIN!!!",
                  (ulong)thread, (ulong)block));
      DBUG_RETURN(1);
    }
  }
  else
  {
    if (mode == PAGECACHE_PIN_LEFT_PINNED)
    {
      DBUG_PRINT("info",
                 ("info_check_pin: thread: 0x%lx block 0x%lx: LEFT_PINNED!!!",
                  (ulong)thread, (ulong)block));
      DBUG_RETURN(1);
    }
    else if (mode == PAGECACHE_UNPIN)
    {
      DBUG_PRINT("info",
                 ("info_check_pin: thread: 0x%lx block 0x%lx: UNPIN!!!",
                  (ulong)thread, (ulong)block));
      DBUG_RETURN(1);
    }
  }
  DBUG_RETURN(0);
}


/*
  Debug function which checks current lock/pin state and requested changes

  SYNOPSIS
    info_check_lock()
    lock                 requested lock changes
    pin                  requested pin changes

  RETURN
    0 - OK
    1 - Error
*/

my_bool info_check_lock(PAGECACHE_BLOCK_LINK *block,
                        enum pagecache_page_lock lock,
                        enum pagecache_page_pin pin)
{
  struct st_my_thread_var *thread= my_thread_var;
  DBUG_ENTER("info_check_lock");
  PAGECACHE_LOCK_INFO *info=
    (PAGECACHE_LOCK_INFO *) info_find((PAGECACHE_PIN_INFO *) block->lock_list,
                                      thread);
  switch(lock)
  {
  case PAGECACHE_LOCK_LEFT_UNLOCKED:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_UNPINNED);
    if (info)
      goto error;
    break;
  case PAGECACHE_LOCK_LEFT_READLOCKED:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_UNPINNED ||
                pin == PAGECACHE_PIN_LEFT_PINNED);
    if (info == 0 || info->write_lock)
      goto error;
    break;
  case PAGECACHE_LOCK_LEFT_WRITELOCKED:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_PINNED);
    if (info == 0 || !info->write_lock)
      goto error;
    break;
  case PAGECACHE_LOCK_READ:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_UNPINNED ||
                pin == PAGECACHE_PIN);
    if (info != 0)
      goto error;
    break;
  case PAGECACHE_LOCK_WRITE:
    DBUG_ASSERT(pin == PAGECACHE_PIN);
    if (info != 0)
      goto error;
    break;
  case PAGECACHE_LOCK_READ_UNLOCK:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_UNPINNED ||
                pin == PAGECACHE_UNPIN);
    if (info == 0 || info->write_lock)
      goto error;
    break;
  case PAGECACHE_LOCK_WRITE_UNLOCK:
    DBUG_ASSERT(pin == PAGECACHE_UNPIN);
    if (info == 0 || !info->write_lock)
      goto error;
    break;
  case PAGECACHE_LOCK_WRITE_TO_READ:
    DBUG_ASSERT(pin == PAGECACHE_PIN_LEFT_PINNED ||
                pin == PAGECACHE_UNPIN);
    if (info == 0 || !info->write_lock)
      goto error;
    break;
  }
  DBUG_RETURN(0);
error:
  DBUG_PRINT("info",
             ("info_check_lock: thread: 0x%lx block 0x%lx: info: %d wrt: %d,"
              "to lock: %s, to pin: %s",
              (ulong)thread, (ulong)block, test(info),
              (info ? info->write_lock : 0),
              page_cache_page_lock_str[lock],
              page_cache_page_pin_str[pin]));
  DBUG_RETURN(1);
}
#endif

#define FLUSH_CACHE         2000            /* sort this many blocks at once */

static int flush_all_key_blocks(PAGECACHE *pagecache);
#ifdef THREAD
static void link_into_queue(PAGECACHE_WQUEUE *wqueue,
                                   struct st_my_thread_var *thread);
static void unlink_from_queue(PAGECACHE_WQUEUE *wqueue,
                                     struct st_my_thread_var *thread);
#endif
static void free_block(PAGECACHE *pagecache, PAGECACHE_BLOCK_LINK *block);
static void test_key_cache(PAGECACHE *pagecache,
                           const char *where, my_bool lock);

#define PAGECACHE_HASH(p, f, pos) (((ulong) (pos) +                          \
                                    (ulong) (f).file) & (p->hash_entries-1))
#define FILE_HASH(f) ((uint) (f).file & (PAGECACHE_CHANGED_BLOCKS_HASH - 1))

#define DEFAULT_PAGECACHE_DEBUG_LOG  "pagecache_debug.log"

#if defined(PAGECACHE_DEBUG) && ! defined(PAGECACHE_DEBUG_LOG)
#define PAGECACHE_DEBUG_LOG  DEFAULT_PAGECACHE_DEBUG_LOG
#endif

#if defined(PAGECACHE_DEBUG_LOG)
static FILE *pagecache_debug_log= NULL;
static void pagecache_debug_print _VARARGS((const char *fmt, ...));
#define PAGECACHE_DEBUG_OPEN                                                  \
          if (!pagecache_debug_log)                                           \
          {                                                                   \
            pagecache_debug_log= fopen(PAGECACHE_DEBUG_LOG, "w");             \
            (void) setvbuf(pagecache_debug_log, NULL, _IOLBF, BUFSIZ);        \
          }

#define PAGECACHE_DEBUG_CLOSE                                                 \
          if (pagecache_debug_log)                                            \
          {                                                                   \
            fclose(pagecache_debug_log);                                      \
            pagecache_debug_log= 0;                                           \
          }
#else
#define PAGECACHE_DEBUG_OPEN
#define PAGECACHE_DEBUG_CLOSE
#endif /* defined(PAGECACHE_DEBUG_LOG) */

#if defined(PAGECACHE_DEBUG_LOG) && defined(PAGECACHE_DEBUG)
#define KEYCACHE_DBUG_PRINT(l, m)                                             \
            { if (pagecache_debug_log)                                        \
                fprintf(pagecache_debug_log, "%s: ", l);                      \
              pagecache_debug_print m; }

#define KEYCACHE_DBUG_ASSERT(a)                                               \
            { if (! (a) && pagecache_debug_log)                               \
                fclose(pagecache_debug_log);                                  \
              assert(a); }
#else
#define KEYCACHE_DBUG_PRINT(l, m)  DBUG_PRINT(l, m)
#define KEYCACHE_DBUG_ASSERT(a)    DBUG_ASSERT(a)
#endif /* defined(PAGECACHE_DEBUG_LOG) && defined(PAGECACHE_DEBUG) */

#if defined(PAGECACHE_DEBUG) || !defined(DBUG_OFF)
#ifdef THREAD
static long pagecache_thread_id;
#define KEYCACHE_THREAD_TRACE(l)                                              \
             KEYCACHE_DBUG_PRINT(l,("|thread %ld",pagecache_thread_id))

#define KEYCACHE_THREAD_TRACE_BEGIN(l)                                        \
            { struct st_my_thread_var *thread_var= my_thread_var;             \
              pagecache_thread_id= thread_var->id;                            \
              KEYCACHE_DBUG_PRINT(l,("[thread %ld",pagecache_thread_id)) }

#define KEYCACHE_THREAD_TRACE_END(l)                                          \
            KEYCACHE_DBUG_PRINT(l,("]thread %ld",pagecache_thread_id))
#else /* THREAD */
#define KEYCACHE_THREAD_TRACE(l)        KEYCACHE_DBUG_PRINT(l,(""))
#define KEYCACHE_THREAD_TRACE_BEGIN(l)  KEYCACHE_DBUG_PRINT(l,(""))
#define KEYCACHE_THREAD_TRACE_END(l)    KEYCACHE_DBUG_PRINT(l,(""))
#endif /* THREAD */
#else
#define KEYCACHE_THREAD_TRACE_BEGIN(l)
#define KEYCACHE_THREAD_TRACE_END(l)
#define KEYCACHE_THREAD_TRACE(l)
#endif /* defined(PAGECACHE_DEBUG) || !defined(DBUG_OFF) */

#define BLOCK_NUMBER(p, b)                                                    \
  ((uint) (((char*)(b)-(char *) p->block_root)/sizeof(PAGECACHE_BLOCK_LINK)))
#define PAGECACHE_HASH_LINK_NUMBER(p, h)                                      \
  ((uint) (((char*)(h)-(char *) p->hash_link_root)/                           \
           sizeof(PAGECACHE_HASH_LINK)))

#if (defined(PAGECACHE_TIMEOUT) && !defined(__WIN__)) || defined(PAGECACHE_DEBUG)
static int pagecache_pthread_cond_wait(pthread_cond_t *cond,
                                      pthread_mutex_t *mutex);
#else
#define  pagecache_pthread_cond_wait pthread_cond_wait
#endif

#if defined(PAGECACHE_DEBUG)
static int ___pagecache_pthread_mutex_lock(pthread_mutex_t *mutex);
static void ___pagecache_pthread_mutex_unlock(pthread_mutex_t *mutex);
static int ___pagecache_pthread_cond_signal(pthread_cond_t *cond);
#define pagecache_pthread_mutex_lock(M) \
{ DBUG_PRINT("lock", ("mutex lock 0x%lx %u", (ulong)(M), __LINE__)); \
  ___pagecache_pthread_mutex_lock(M);}
#define pagecache_pthread_mutex_unlock(M) \
{ DBUG_PRINT("lock", ("mutex unlock 0x%lx %u", (ulong)(M), __LINE__)); \
  ___pagecache_pthread_mutex_unlock(M);}
#define pagecache_pthread_cond_signal(M) \
{ DBUG_PRINT("lock", ("signal 0x%lx %u", (ulong)(M), __LINE__)); \
  ___pagecache_pthread_cond_signal(M);}
#else
#define pagecache_pthread_mutex_lock pthread_mutex_lock
#define pagecache_pthread_mutex_unlock pthread_mutex_unlock
#define pagecache_pthread_cond_signal pthread_cond_signal
#endif /* defined(PAGECACHE_DEBUG) */


/*
  Write page to the disk

  SYNOPSIS
    pagecache_fwrite()
    pagecache - page cache pointer
    filedesc  - pagecache file descriptor structure
    buffer    - buffer which we will write
    type      - page type (plain or with LSN)
    flags     - MYF() flags

  RETURN
    0   - OK
    !=0 - Error
*/
uint pagecache_fwrite(PAGECACHE *pagecache,
                      PAGECACHE_FILE *filedesc,
                      byte *buffer,
                      maria_page_no_t pageno,
                      enum pagecache_page_type type,
                      myf flags)
{
  DBUG_ENTER("pagecache_fwrite");
  if (type == PAGECACHE_LSN_PAGE)
  {
    DBUG_PRINT("info", ("Log handler call"));
    /* TODO: put here loghandler call */
  }
  DBUG_RETURN(my_pwrite(filedesc->file, buffer, pagecache->block_size,
                        (pageno)<<(pagecache->shift), flags));
}


/*
  Read page from the disk

  SYNOPSIS
    pagecache_fread()
    pagecache - page cache pointer
    filedesc  - pagecache file descriptor structure
    buffer    - buffer in which we will read
    pageno    - page number
    flags     - MYF() flags
*/
#define pagecache_fread(pagecache, filedesc, buffer, pageno, flags) \
  my_pread((filedesc)->file, buffer, pagecache->block_size,         \
           (pageno)<<(pagecache->shift), flags)


/*
  next_power(value) is 2 at the power of (1+floor(log2(value)));
  e.g. next_power(2)=4, next_power(3)=4.
*/
static uint next_power(uint value)
{
  uint old_value= 1;
  while (value)
  {
    old_value= value;
    value&= value-1;
  }
  return (old_value << 1);
}


/*
  Initialize a page cache

  SYNOPSIS
    init_pagecache()
    pagecache			pointer to a page cache data structure
    key_cache_block_size	size of blocks to keep cached data
    use_mem                     total memory to use for the key cache
    division_limit		division limit (may be zero)
    age_threshold		age threshold (may be zero)
    block_size                  size of block (should be power of 2)
    loghandler                  logfandler pointer to call it in case of
                                pages with LSN

  RETURN VALUE
    number of blocks in the key cache, if successful,
    0 - otherwise.

  NOTES.
    if pagecache->inited != 0 we assume that the key cache
    is already initialized.  This is for now used by myisamchk, but shouldn't
    be something that a program should rely on!

    It's assumed that no two threads call this function simultaneously
    referring to the same key cache handle.

*/

int init_pagecache(PAGECACHE *pagecache, my_size_t use_mem,
                   uint division_limit, uint age_threshold,
                   uint block_size,
                   LOG_HANDLER *loghandler)
{
  int blocks, hash_links, length;
  int error;
  DBUG_ENTER("init_key_cache");
  DBUG_ASSERT(block_size >= 512);

  PAGECACHE_DEBUG_OPEN;
  if (pagecache->inited && pagecache->disk_blocks > 0)
  {
    DBUG_PRINT("warning",("key cache already in use"));
    DBUG_RETURN(0);
  }

  pagecache->loghandler= loghandler;

  pagecache->global_cache_w_requests= pagecache->global_cache_r_requests= 0;
  pagecache->global_cache_read= pagecache->global_cache_write= 0;
  pagecache->disk_blocks= -1;
  if (! pagecache->inited)
  {
    pagecache->inited= 1;
    pagecache->in_init= 0;
    pthread_mutex_init(&pagecache->cache_lock, MY_MUTEX_INIT_FAST);
    pagecache->resize_queue.last_thread= NULL;
  }

  pagecache->mem_size= use_mem;
  pagecache->block_size= block_size;
  pagecache->shift= my_bit_log2(block_size);
  DBUG_PRINT("info", ("block_size: %u",
		      block_size));
  DBUG_ASSERT(((uint)(1 << pagecache->shift)) == block_size);

  blocks= (int) (use_mem / (sizeof(PAGECACHE_BLOCK_LINK) +
                            2 * sizeof(PAGECACHE_HASH_LINK) +
                            sizeof(PAGECACHE_HASH_LINK*) *
                            5/4 + block_size));
  /* It doesn't make sense to have too few blocks (less than 8) */
  if (blocks >= 8 && pagecache->disk_blocks < 0)
  {
    for ( ; ; )
    {
      /* Set my_hash_entries to the next bigger 2 power */
      if ((pagecache->hash_entries= next_power((uint)blocks)) <
          ((uint)blocks) * 5/4)
        pagecache->hash_entries<<= 1;
      hash_links= 2 * blocks;
#if defined(MAX_THREADS)
      if (hash_links < MAX_THREADS + blocks - 1)
        hash_links= MAX_THREADS + blocks - 1;
#endif
      while ((length= (ALIGN_SIZE(blocks * sizeof(PAGECACHE_BLOCK_LINK)) +
		       ALIGN_SIZE(hash_links * sizeof(PAGECACHE_HASH_LINK)) +
		       ALIGN_SIZE(sizeof(PAGECACHE_HASH_LINK*) *
                                  pagecache->hash_entries))) +
	     ((ulong) blocks << pagecache->shift) > use_mem)
        blocks--;
      /* Allocate memory for cache page buffers */
      if ((pagecache->block_mem=
	   my_large_malloc((ulong) blocks * pagecache->block_size,
			  MYF(MY_WME))))
      {
        /*
	  Allocate memory for blocks, hash_links and hash entries;
	  For each block 2 hash links are allocated
        */
        if ((pagecache->block_root=
             (PAGECACHE_BLOCK_LINK*) my_malloc((uint) length,
                                                           MYF(0))))
          break;
        my_large_free(pagecache->block_mem, MYF(0));
        pagecache->block_mem= 0;
      }
      if (blocks < 8)
      {
        my_errno= ENOMEM;
        goto err;
      }
      blocks= blocks / 4*3;
    }
    pagecache->blocks_unused= (ulong) blocks;
    pagecache->disk_blocks= (int) blocks;
    pagecache->hash_links= hash_links;
    pagecache->hash_root=
      (PAGECACHE_HASH_LINK**) ((char*) pagecache->block_root +
                               ALIGN_SIZE(blocks*sizeof(PAGECACHE_BLOCK_LINK)));
    pagecache->hash_link_root=
      (PAGECACHE_HASH_LINK*) ((char*) pagecache->hash_root +
                              ALIGN_SIZE((sizeof(PAGECACHE_HASH_LINK*) *
                                          pagecache->hash_entries)));
    bzero((byte*) pagecache->block_root,
	  pagecache->disk_blocks * sizeof(PAGECACHE_BLOCK_LINK));
    bzero((byte*) pagecache->hash_root,
          pagecache->hash_entries * sizeof(PAGECACHE_HASH_LINK*));
    bzero((byte*) pagecache->hash_link_root,
	  pagecache->hash_links * sizeof(PAGECACHE_HASH_LINK));
    pagecache->hash_links_used= 0;
    pagecache->free_hash_list= NULL;
    pagecache->blocks_used= pagecache->blocks_changed= 0;

    pagecache->global_blocks_changed= 0;
    pagecache->blocks_available=0;		/* For debugging */

    /* The LRU chain is empty after initialization */
    pagecache->used_last= NULL;
    pagecache->used_ins= NULL;
    pagecache->free_block_list= NULL;
    pagecache->time= 0;
    pagecache->warm_blocks= 0;
    pagecache->min_warm_blocks= (division_limit ?
                                 blocks * division_limit / 100 + 1 :
                                 (ulong)blocks);
    pagecache->age_threshold= (age_threshold ?
                               blocks * age_threshold / 100 :
                               (ulong)blocks);

    pagecache->cnt_for_resize_op= 0;
    pagecache->resize_in_flush= 0;
    pagecache->can_be_used= 1;

    pagecache->waiting_for_hash_link.last_thread= NULL;
    pagecache->waiting_for_block.last_thread= NULL;
    DBUG_PRINT("exit",
	       ("disk_blocks: %d  block_root: 0x%lx  hash_entries: %d\
 hash_root: 0x%lx  hash_links: %d  hash_link_root: 0x%lx",
		pagecache->disk_blocks, pagecache->block_root,
		pagecache->hash_entries, pagecache->hash_root,
		pagecache->hash_links, pagecache->hash_link_root));
    bzero((gptr) pagecache->changed_blocks,
	  sizeof(pagecache->changed_blocks[0]) *
          PAGECACHE_CHANGED_BLOCKS_HASH);
    bzero((gptr) pagecache->file_blocks,
	  sizeof(pagecache->file_blocks[0]) *
          PAGECACHE_CHANGED_BLOCKS_HASH);
  }

  pagecache->blocks= pagecache->disk_blocks > 0 ? pagecache->disk_blocks : 0;
  DBUG_RETURN((uint) pagecache->blocks);

err:
  error= my_errno;
  pagecache->disk_blocks= 0;
  pagecache->blocks=  0;
  if (pagecache->block_mem)
  {
    my_large_free((gptr) pagecache->block_mem, MYF(0));
    pagecache->block_mem= NULL;
  }
  if (pagecache->block_root)
  {
    my_free((gptr) pagecache->block_root, MYF(0));
    pagecache->block_root= NULL;
  }
  my_errno= error;
  pagecache->can_be_used= 0;
  DBUG_RETURN(0);
}


/*
  Resize a key cache

  SYNOPSIS
    resize_pagecache()
    pagecache                   pointer to a page cache data structure
    use_mem			total memory to use for the new key cache
    division_limit		new division limit (if not zero)
    age_threshold		new age threshold (if not zero)

  RETURN VALUE
    number of blocks in the key cache, if successful,
    0 - otherwise.

  NOTES.
    The function first compares the memory size parameter
    with the key cache value.

    If they differ the function free the the memory allocated for the
    old key cache blocks by calling the end_pagecache function and
    then rebuilds the key cache with new blocks by calling
    init_key_cache.

    The function starts the operation only when all other threads
    performing operations with the key cache let her to proceed
    (when cnt_for_resize=0).
*/

int resize_pagecache(PAGECACHE *pagecache,
		     my_size_t use_mem, uint division_limit,
		     uint age_threshold)
{
  int blocks;
  struct st_my_thread_var *thread;
  PAGECACHE_WQUEUE *wqueue;
  DBUG_ENTER("resize_pagecache");

  if (!pagecache->inited)
    DBUG_RETURN(pagecache->disk_blocks);

  if(use_mem == pagecache->mem_size)
  {
    change_pagecache_param(pagecache, division_limit, age_threshold);
    DBUG_RETURN(pagecache->disk_blocks);
  }

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);

#ifdef THREAD
  wqueue= &pagecache->resize_queue;
  thread= my_thread_var;
  link_into_queue(wqueue, thread);

  while (wqueue->last_thread->next != thread)
  {
    pagecache_pthread_cond_wait(&thread->suspend, &pagecache->cache_lock);
  }
#endif

  pagecache->resize_in_flush= 1;
  if (flush_all_key_blocks(pagecache))
  {
    /* TODO: if this happens, we should write a warning in the log file ! */
    pagecache->resize_in_flush= 0;
    blocks= 0;
    pagecache->can_be_used= 0;
    goto finish;
  }
  pagecache->resize_in_flush= 0;
  pagecache->can_be_used= 0;
#ifdef THREAD
  while (pagecache->cnt_for_resize_op)
  {
    KEYCACHE_DBUG_PRINT("resize_pagecache: wait",
                        ("suspend thread %ld", thread->id));
    pagecache_pthread_cond_wait(&thread->suspend, &pagecache->cache_lock);
  }
#else
  KEYCACHE_DBUG_ASSERT(pagecache->cnt_for_resize_op == 0);
#endif

  end_pagecache(pagecache, 0);			/* Don't free mutex */
  /* The following will work even if use_mem is 0 */
  blocks= init_pagecache(pagecache, pagecache->block_size, use_mem,
			 division_limit, age_threshold,
                         pagecache->loghandler);

finish:
#ifdef THREAD
  unlink_from_queue(wqueue, thread);
  /* Signal for the next resize request to proceeed if any */
  if (wqueue->last_thread)
  {
    KEYCACHE_DBUG_PRINT("resize_pagecache: signal",
                        ("thread %ld", wqueue->last_thread->next->id));
    pagecache_pthread_cond_signal(&wqueue->last_thread->next->suspend);
  }
#endif
  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
  DBUG_RETURN(blocks);
}


/*
  Increment counter blocking resize key cache operation
*/
static inline void inc_counter_for_resize_op(PAGECACHE *pagecache)
{
  pagecache->cnt_for_resize_op++;
}


/*
  Decrement counter blocking resize key cache operation;
  Signal the operation to proceed when counter becomes equal zero
*/
static inline void dec_counter_for_resize_op(PAGECACHE *pagecache)
{
#ifdef THREAD
  struct st_my_thread_var *last_thread;
  if (!--pagecache->cnt_for_resize_op &&
      (last_thread= pagecache->resize_queue.last_thread))
  {
    KEYCACHE_DBUG_PRINT("dec_counter_for_resize_op: signal",
                        ("thread %ld", last_thread->next->id));
    pagecache_pthread_cond_signal(&last_thread->next->suspend);
  }
#else
  pagecache->cnt_for_resize_op--;
#endif
}

/*
  Change the page cache parameters

  SYNOPSIS
    change_pagecache_param()
    pagecache			pointer to a page cache data structure
    division_limit		new division limit (if not zero)
    age_threshold		new age threshold (if not zero)

  RETURN VALUE
    none

  NOTES.
    Presently the function resets the key cache parameters
    concerning midpoint insertion strategy - division_limit and
    age_threshold.
*/

void change_pagecache_param(PAGECACHE *pagecache, uint division_limit,
			    uint age_threshold)
{
  DBUG_ENTER("change_pagecache_param");

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  if (division_limit)
    pagecache->min_warm_blocks= (pagecache->disk_blocks *
				division_limit / 100 + 1);
  if (age_threshold)
    pagecache->age_threshold=   (pagecache->disk_blocks *
				age_threshold / 100);
  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
  DBUG_VOID_RETURN;
}


/*
  Flushes and removes page cache from memory

  SYNOPSIS
    end_pagecache()
    pagecache		page cache handle
    cleanup		Complete free (Free also mutex for key cache)

  RETURN VALUE
    none
*/

void end_pagecache(PAGECACHE *pagecache, my_bool cleanup)
{
  DBUG_ENTER("end_pagecache");
  DBUG_PRINT("enter", ("key_cache: 0x%lx", pagecache));

  if (!pagecache->inited)
    DBUG_VOID_RETURN;

  if (pagecache->disk_blocks > 0)
  {
    if (pagecache->block_mem)
    {
      my_large_free((gptr) pagecache->block_mem, MYF(0));
      pagecache->block_mem= NULL;
      my_free((gptr) pagecache->block_root, MYF(0));
      pagecache->block_root= NULL;
    }
    pagecache->disk_blocks= -1;
    /* Reset blocks_changed to be safe if flush_all_key_blocks is called */
    pagecache->blocks_changed= 0;
  }

  DBUG_PRINT("status", ("used: %d  changed: %d  w_requests: %lu  "
                        "writes: %lu  r_requests: %lu  reads: %lu",
                        pagecache->blocks_used, pagecache->global_blocks_changed,
                        (ulong) pagecache->global_cache_w_requests,
                        (ulong) pagecache->global_cache_write,
                        (ulong) pagecache->global_cache_r_requests,
                        (ulong) pagecache->global_cache_read));

  if (cleanup)
  {
    pthread_mutex_destroy(&pagecache->cache_lock);
    pagecache->inited= pagecache->can_be_used= 0;
    PAGECACHE_DEBUG_CLOSE;
  }
  DBUG_VOID_RETURN;
} /* end_pagecache */


#ifdef THREAD
/*
  Link a thread into double-linked queue of waiting threads.

  SYNOPSIS
    link_into_queue()
      wqueue              pointer to the queue structure
      thread              pointer to the thread to be added to the queue

  RETURN VALUE
    none

  NOTES.
    Queue is represented by a circular list of the thread structures
    The list is double-linked of the type (**prev,*next), accessed by
    a pointer to the last element.
*/

static void link_into_queue(PAGECACHE_WQUEUE *wqueue,
                            struct st_my_thread_var *thread)
{
  struct st_my_thread_var *last;
  if (! (last= wqueue->last_thread))
  {
    /* Queue is empty */
    thread->next= thread;
    thread->prev= &thread->next;
  }
  else
  {
    thread->prev= last->next->prev;
    last->next->prev= &thread->next;
    thread->next= last->next;
    last->next= thread;
  }
  wqueue->last_thread= thread;
}

/*
  Unlink a thread from double-linked queue of waiting threads

  SYNOPSIS
    unlink_from_queue()
      wqueue              pointer to the queue structure
      thread              pointer to the thread to be removed from the queue

  RETURN VALUE
    none

  NOTES.
    See NOTES for link_into_queue
*/

static void unlink_from_queue(PAGECACHE_WQUEUE *wqueue,
                                     struct st_my_thread_var *thread)
{
  KEYCACHE_DBUG_PRINT("unlink_from_queue", ("thread %ld", thread->id));
  if (thread->next == thread)
    /* The queue contains only one member */
    wqueue->last_thread= NULL;
  else
  {
    thread->next->prev= thread->prev;
    *thread->prev=thread->next;
    if (wqueue->last_thread == thread)
      wqueue->last_thread= STRUCT_PTR(struct st_my_thread_var, next,
                                      thread->prev);
  }
  thread->next= NULL;
}


/*
  Add a thread to single-linked queue of waiting threads

  SYNOPSIS
    add_to_queue()
      wqueue              pointer to the queue structure
      thread              pointer to the thread to be added to the queue

  RETURN VALUE
    none

  NOTES.
    Queue is represented by a circular list of the thread structures
    The list is single-linked of the type (*next), accessed by a pointer
    to the last element.
*/

static inline void add_to_queue(PAGECACHE_WQUEUE *wqueue,
                                struct st_my_thread_var *thread)
{
  struct st_my_thread_var *last;
  if (! (last= wqueue->last_thread))
    thread->next= thread;
  else
  {
    thread->next= last->next;
    last->next= thread;
  }
  wqueue->last_thread= thread;
}


/*
  Remove all threads from queue signaling them to proceed

  SYNOPSIS
    realease_queue()
      wqueue              pointer to the queue structure
      thread              pointer to the thread to be added to the queue

  RETURN VALUE
    none

  NOTES.
    See notes for add_to_queue
    When removed from the queue each thread is signaled via condition
    variable thread->suspend.
*/

static void release_queue(PAGECACHE_WQUEUE *wqueue)
{
  struct st_my_thread_var *last= wqueue->last_thread;
  struct st_my_thread_var *next= last->next;
  struct st_my_thread_var *thread;
  do
  {
    thread=next;
    KEYCACHE_DBUG_PRINT("release_queue: signal", ("thread %ld", thread->id));
    pagecache_pthread_cond_signal(&thread->suspend);
    next=thread->next;
    thread->next= NULL;
  }
  while (thread != last);
  wqueue->last_thread= NULL;
}
#endif


/*
  Unlink a block from the chain of dirty/clean blocks
*/

static inline void unlink_changed(PAGECACHE_BLOCK_LINK *block)
{
  if (block->next_changed)
    block->next_changed->prev_changed= block->prev_changed;
  *block->prev_changed= block->next_changed;
}


/*
  Link a block into the chain of dirty/clean blocks
*/

static inline void link_changed(PAGECACHE_BLOCK_LINK *block,
                                PAGECACHE_BLOCK_LINK **phead)
{
  block->prev_changed= phead;
  if ((block->next_changed= *phead))
    (*phead)->prev_changed= &block->next_changed;
  *phead= block;
}


/*
  Unlink a block from the chain of dirty/clean blocks, if it's asked for,
  and link it to the chain of clean blocks for the specified file
*/

static void link_to_file_list(PAGECACHE *pagecache,
                              PAGECACHE_BLOCK_LINK *block,
                              PAGECACHE_FILE *file, my_bool unlink)
{
  if (unlink)
    unlink_changed(block);
  link_changed(block, &pagecache->file_blocks[FILE_HASH(*file)]);
  if (block->status & BLOCK_CHANGED)
  {
    block->status&= ~BLOCK_CHANGED;
    pagecache->blocks_changed--;
    pagecache->global_blocks_changed--;
  }
}


/*
  Unlink a block from the chain of clean blocks for the specified
  file and link it to the chain of dirty blocks for this file
*/

static inline void link_to_changed_list(PAGECACHE *pagecache,
                                        PAGECACHE_BLOCK_LINK *block)
{
  unlink_changed(block);
  link_changed(block,
               &pagecache->changed_blocks[FILE_HASH(block->hash_link->file)]);
  block->status|=BLOCK_CHANGED;
  pagecache->blocks_changed++;
  pagecache->global_blocks_changed++;
}


/*
  Link a block to the LRU chain at the beginning or at the end of
  one of two parts.

  SYNOPSIS
    link_block()
      pagecache            pointer to a page cache data structure
      block               pointer to the block to link to the LRU chain
      hot                 <-> to link the block into the hot subchain
      at_end              <-> to link the block at the end of the subchain

  RETURN VALUE
    none

  NOTES.
    The LRU chain is represented by a curcular list of block structures.
    The list is double-linked of the type (**prev,*next) type.
    The LRU chain is divided into two parts - hot and warm.
    There are two pointers to access the last blocks of these two
    parts. The beginning of the warm part follows right after the
    end of the hot part.
    Only blocks of the warm part can be used for replacement.
    The first block from the beginning of this subchain is always
    taken for eviction (pagecache->last_used->next)

    LRU chain:       +------+   H O T    +------+
                +----| end  |----...<----| beg  |----+
                |    +------+last        +------+    |
                v<-link in latest hot (new end)      |
                |     link in latest warm (new end)->^
                |    +------+  W A R M   +------+    |
                +----| beg  |---->...----| end  |----+
                     +------+            +------+ins
                  first for eviction
*/

static void link_block(PAGECACHE *pagecache, PAGECACHE_BLOCK_LINK *block,
                       my_bool hot, my_bool at_end)
{
  PAGECACHE_BLOCK_LINK *ins;
  PAGECACHE_BLOCK_LINK **ptr_ins;

  KEYCACHE_DBUG_ASSERT(! (block->hash_link && block->hash_link->requests));
#ifdef THREAD
  if (!hot && pagecache->waiting_for_block.last_thread)
  {
    /* Signal that in the LRU warm sub-chain an available block has appeared */
    struct st_my_thread_var *last_thread=
                               pagecache->waiting_for_block.last_thread;
    struct st_my_thread_var *first_thread= last_thread->next;
    struct st_my_thread_var *next_thread= first_thread;
    PAGECACHE_HASH_LINK *hash_link=
      (PAGECACHE_HASH_LINK *) first_thread->opt_info;
    struct st_my_thread_var *thread;
    do
    {
      thread= next_thread;
      next_thread= thread->next;
      /*
         We notify about the event all threads that ask
         for the same page as the first thread in the queue
      */
      if ((PAGECACHE_HASH_LINK *) thread->opt_info == hash_link)
      {
        KEYCACHE_DBUG_PRINT("link_block: signal", ("thread %ld", thread->id));
        pagecache_pthread_cond_signal(&thread->suspend);
        unlink_from_queue(&pagecache->waiting_for_block, thread);
        block->requests++;
      }
    }
    while (thread != last_thread);
    hash_link->block= block;
    KEYCACHE_THREAD_TRACE("link_block: after signaling");
#if defined(PAGECACHE_DEBUG)
    KEYCACHE_DBUG_PRINT("link_block",
        ("linked,unlinked block %u  status=%x  #requests=%u  #available=%u",
         BLOCK_NUMBER(pagecache, block), block->status,
         block->requests, pagecache->blocks_available));
#endif
    return;
  }
#else /* THREAD */
  KEYCACHE_DBUG_ASSERT(! (!hot && pagecache->waiting_for_block.last_thread));
      /* Condition not transformed using DeMorgan, to keep the text identical */
#endif /* THREAD */
  ptr_ins= hot ? &pagecache->used_ins : &pagecache->used_last;
  ins= *ptr_ins;
  if (ins)
  {
    ins->next_used->prev_used= &block->next_used;
    block->next_used= ins->next_used;
    block->prev_used= &ins->next_used;
    ins->next_used= block;
    if (at_end)
      *ptr_ins= block;
  }
  else
  {
    /* The LRU chain is empty */
    pagecache->used_last= pagecache->used_ins= block->next_used= block;
    block->prev_used= &block->next_used;
  }
  KEYCACHE_THREAD_TRACE("link_block");
#if defined(PAGECACHE_DEBUG)
  pagecache->blocks_available++;
  KEYCACHE_DBUG_PRINT("link_block",
      ("linked block %u:%1u  status=%x  #requests=%u  #available=%u",
       BLOCK_NUMBER(pagecache, block), at_end, block->status,
       block->requests, pagecache->blocks_available));
  KEYCACHE_DBUG_ASSERT((ulong) pagecache->blocks_available <=
                       pagecache->blocks_used);
#endif
}


/*
  Unlink a block from the LRU chain

  SYNOPSIS
    unlink_block()
      pagecache            pointer to a page cache data structure
      block               pointer to the block to unlink from the LRU chain

  RETURN VALUE
    none

  NOTES.
    See NOTES for link_block
*/

static void unlink_block(PAGECACHE *pagecache, PAGECACHE_BLOCK_LINK *block)
{
  if (block->next_used == block)
    /* The list contains only one member */
    pagecache->used_last= pagecache->used_ins= NULL;
  else
  {
    block->next_used->prev_used= block->prev_used;
    *block->prev_used= block->next_used;
    if (pagecache->used_last == block)
      pagecache->used_last= STRUCT_PTR(PAGECACHE_BLOCK_LINK,
                                       next_used, block->prev_used);
    if (pagecache->used_ins == block)
      pagecache->used_ins= STRUCT_PTR(PAGECACHE_BLOCK_LINK,
                                      next_used, block->prev_used);
  }
  block->next_used= NULL;

  KEYCACHE_THREAD_TRACE("unlink_block");
#if defined(PAGECACHE_DEBUG)
  pagecache->blocks_available--;
  KEYCACHE_DBUG_PRINT("unlink_block",
    ("unlinked block 0x%lx (%u) status=%x   #requests=%u  #available=%u",
     (ulong)block, BLOCK_NUMBER(pagecache, block), block->status,
     block->requests, pagecache->blocks_available));
  BLOCK_INFO(block);
  KEYCACHE_DBUG_ASSERT(pagecache->blocks_available >= 0);
#endif
}


/*
  Register requests for a block

  SYNOPSIS
    reg_requests()
    pagecache            this page cache reference
    block                the block we request reference
    count                how many requests we register (it is 1 everywhere)

  NOTE
  Registration of request means we are going to use this block so we exclude
  it from the LRU if it is first request
*/
static void reg_requests(PAGECACHE *pagecache, PAGECACHE_BLOCK_LINK *block,
                         int count)
{
  DBUG_ENTER("reg_requests");
  DBUG_PRINT("enter", ("block 0x%lx (%u) status=%x, reqs: %u",
		       (ulong)block, BLOCK_NUMBER(pagecache, block),
                       block->status, block->requests));
  BLOCK_INFO(block);
  if (! block->requests)
    /* First request for the block unlinks it */
    unlink_block(pagecache, block);
  block->requests+= count;
  DBUG_VOID_RETURN;
}


/*
  Unregister request for a block
  linking it to the LRU chain if it's the last request

  SYNOPSIS
    unreg_request()
    pagecache            pointer to a page cache data structure
    block               pointer to the block to link to the LRU chain
    at_end              <-> to link the block at the end of the LRU chain

  RETURN VALUE
    none

  NOTES.
    Every linking to the LRU chain decrements by one a special block
    counter (if it's positive). If the at_end parameter is TRUE the block is
    added either at the end of warm sub-chain or at the end of hot sub-chain.
    It is added to the hot subchain if its counter is zero and number of
    blocks in warm sub-chain is not less than some low limit (determined by
    the division_limit parameter). Otherwise the block is added to the warm
    sub-chain. If the at_end parameter is FALSE the block is always added
    at beginning of the warm sub-chain.
    Thus a warm block can be promoted to the hot sub-chain when its counter
    becomes zero for the first time.
    At the same time  the block at the very beginning of the hot subchain
    might be moved to the beginning of the warm subchain if it stays untouched
    for a too long time (this time is determined by parameter age_threshold).
*/

static void unreg_request(PAGECACHE *pagecache,
                          PAGECACHE_BLOCK_LINK *block, int at_end)
{
  DBUG_ENTER("unreg_request");
  DBUG_PRINT("enter", ("block 0x%lx (%u) status=%x, reqs: %u",
		       (ulong)block, BLOCK_NUMBER(pagecache, block),
                       block->status, block->requests));
  BLOCK_INFO(block);
  if (! --block->requests)
  {
    my_bool hot;
    if (block->hits_left)
      block->hits_left--;
    hot= !block->hits_left && at_end &&
      pagecache->warm_blocks > pagecache->min_warm_blocks;
    if (hot)
    {
      if (block->temperature == BLOCK_WARM)
        pagecache->warm_blocks--;
      block->temperature= BLOCK_HOT;
      KEYCACHE_DBUG_PRINT("unreg_request", ("#warm_blocks=%u",
                           pagecache->warm_blocks));
    }
    link_block(pagecache, block, hot, (my_bool)at_end);
    block->last_hit_time= pagecache->time;
    pagecache->time++;

    block= pagecache->used_ins;
    /* Check if we should link a hot block to the warm block */
    if (block && pagecache->time - block->last_hit_time >
	pagecache->age_threshold)
    {
      unlink_block(pagecache, block);
      link_block(pagecache, block, 0, 0);
      if (block->temperature != BLOCK_WARM)
      {
        pagecache->warm_blocks++;
        block->temperature= BLOCK_WARM;
      }
      KEYCACHE_DBUG_PRINT("unreg_request", ("#warm_blocks=%u",
                           pagecache->warm_blocks));
    }
  }
  DBUG_VOID_RETURN;
}

/*
  Remove a reader of the page in block
*/

static inline void remove_reader(PAGECACHE_BLOCK_LINK *block)
{
  DBUG_ENTER("remove_reader");
  BLOCK_INFO(block);
  if (! --block->hash_link->requests && block->condvar)
    pagecache_pthread_cond_signal(block->condvar);
  DBUG_VOID_RETURN;
}


/*
  Wait until the last reader of the page in block
  signals on its termination
*/

static inline void wait_for_readers(PAGECACHE *pagecache,
                                    PAGECACHE_BLOCK_LINK *block)
{
#ifdef THREAD
  struct st_my_thread_var *thread= my_thread_var;
  while (block->hash_link->requests)
  {
    KEYCACHE_DBUG_PRINT("wait_for_readers: wait",
                        ("suspend thread %ld  block %u",
                         thread->id, BLOCK_NUMBER(pagecache, block)));
    block->condvar= &thread->suspend;
    pagecache_pthread_cond_wait(&thread->suspend, &pagecache->cache_lock);
    block->condvar= NULL;
  }
#else
  KEYCACHE_DBUG_ASSERT(block->hash_link->requests == 0);
#endif
}


/*
  Add a hash link to a bucket in the hash_table
*/

static inline void link_hash(PAGECACHE_HASH_LINK **start,
                             PAGECACHE_HASH_LINK *hash_link)
{
  if (*start)
    (*start)->prev= &hash_link->next;
  hash_link->next= *start;
  hash_link->prev= start;
  *start= hash_link;
}


/*
  Remove a hash link from the hash table
*/

static void unlink_hash(PAGECACHE *pagecache, PAGECACHE_HASH_LINK *hash_link)
{
  KEYCACHE_DBUG_PRINT("unlink_hash", ("fd: %u  pos_ %lu  #requests=%u",
      (uint) hash_link->file.file, (ulong) hash_link->pageno,
      hash_link->requests));
  KEYCACHE_DBUG_ASSERT(hash_link->requests == 0);
  if ((*hash_link->prev= hash_link->next))
    hash_link->next->prev= hash_link->prev;
  hash_link->block= NULL;
#ifdef THREAD
  if (pagecache->waiting_for_hash_link.last_thread)
  {
    /* Signal that a free hash link has appeared */
    struct st_my_thread_var *last_thread=
                               pagecache->waiting_for_hash_link.last_thread;
    struct st_my_thread_var *first_thread= last_thread->next;
    struct st_my_thread_var *next_thread= first_thread;
    PAGECACHE_PAGE *first_page= (PAGECACHE_PAGE *) (first_thread->opt_info);
    struct st_my_thread_var *thread;

    hash_link->file= first_page->file;
    hash_link->pageno= first_page->pageno;
    do
    {
      PAGECACHE_PAGE *page;
      thread= next_thread;
      page= (PAGECACHE_PAGE *) thread->opt_info;
      next_thread= thread->next;
      /*
         We notify about the event all threads that ask
         for the same page as the first thread in the queue
      */
      if (page->file.file == hash_link->file.file &&
          page->pageno == hash_link->pageno)
      {
        KEYCACHE_DBUG_PRINT("unlink_hash: signal", ("thread %ld", thread->id));
        pagecache_pthread_cond_signal(&thread->suspend);
        unlink_from_queue(&pagecache->waiting_for_hash_link, thread);
      }
    }
    while (thread != last_thread);
    link_hash(&pagecache->hash_root[PAGECACHE_HASH(pagecache,
                                                   hash_link->file,
                                                   hash_link->pageno)],
              hash_link);
    return;
  }
#else /* THREAD */
  KEYCACHE_DBUG_ASSERT(! (pagecache->waiting_for_hash_link.last_thread));
#endif /* THREAD */
  hash_link->next= pagecache->free_hash_list;
  pagecache->free_hash_list= hash_link;
}


/*
  Get the hash link for the page if it is in the cache (do not put the
  page in the cache if it is absent there)

  SYNOPSIS
    get_present_hash_link()
    pagecache            Pagecache reference
    file                 file ID
    pageno               page number in the file
    start                where to put pointer to found hash link (for
                         direct referring it)

  RETURN
    found hashlink pointer
*/

static PAGECACHE_HASH_LINK *get_present_hash_link(PAGECACHE *pagecache,
                                                  PAGECACHE_FILE *file,
                                                  maria_page_no_t pageno,
                                                  PAGECACHE_HASH_LINK ***start)
{
  reg1 PAGECACHE_HASH_LINK *hash_link;
#if defined(PAGECACHE_DEBUG)
  int cnt;
#endif
  DBUG_ENTER("get_present_hash_link");

  KEYCACHE_DBUG_PRINT("get_present_hash_link", ("fd: %u  pos: %lu",
                      (uint) file->file, (ulong) pageno));

  /*
     Find the bucket in the hash table for the pair (file, pageno);
     start contains the head of the bucket list,
     hash_link points to the first member of the list
  */
  hash_link= *(*start= &pagecache->hash_root[PAGECACHE_HASH(pagecache,
                                                            *file, pageno)]);
#if defined(PAGECACHE_DEBUG)
  cnt= 0;
#endif
  /* Look for an element for the pair (file, pageno) in the bucket chain */
  while (hash_link &&
         (hash_link->pageno != pageno ||
          hash_link->file.file != file->file))
  {
    hash_link= hash_link->next;
#if defined(PAGECACHE_DEBUG)
    cnt++;
    if (! (cnt <= pagecache->hash_links_used))
    {
      int i;
      for (i=0, hash_link= **start ;
           i < cnt ; i++, hash_link= hash_link->next)
      {
        KEYCACHE_DBUG_PRINT("get_present_hash_link", ("fd: %u  pos: %lu",
            (uint) hash_link->file.file, (ulong) hash_link->pageno));
      }
    }
    KEYCACHE_DBUG_ASSERT(cnt <= pagecache->hash_links_used);
#endif
  }
  DBUG_RETURN(hash_link);
}


/*
  Get the hash link for a page
*/

static PAGECACHE_HASH_LINK *get_hash_link(PAGECACHE *pagecache,
                                          PAGECACHE_FILE *file,
                                          maria_page_no_t pageno)
{
  reg1 PAGECACHE_HASH_LINK *hash_link;
  PAGECACHE_HASH_LINK **start;
  PAGECACHE_PAGE page;

  KEYCACHE_DBUG_PRINT("get_hash_link", ("fd: %u  pos: %lu",
                      (uint) file->file, (ulong) pageno));

restart:
  /* try to find the page in the cache */
  hash_link= get_present_hash_link(pagecache, file, pageno,
                                   &start);
  if (! hash_link)
  {
    /* There is no hash link in the hash table for the pair (file, pageno) */
    if (pagecache->free_hash_list)
    {
      hash_link= pagecache->free_hash_list;
      pagecache->free_hash_list= hash_link->next;
    }
    else if (pagecache->hash_links_used < pagecache->hash_links)
    {
      hash_link= &pagecache->hash_link_root[pagecache->hash_links_used++];
    }
    else
    {
#ifdef THREAD
      /* Wait for a free hash link */
      struct st_my_thread_var *thread= my_thread_var;
      KEYCACHE_DBUG_PRINT("get_hash_link", ("waiting"));
      page.file= *file;
      page.pageno= pageno;
      thread->opt_info= (void *) &page;
      link_into_queue(&pagecache->waiting_for_hash_link, thread);
      KEYCACHE_DBUG_PRINT("get_hash_link: wait",
                        ("suspend thread %ld", thread->id));
      pagecache_pthread_cond_wait(&thread->suspend,
                                 &pagecache->cache_lock);
      thread->opt_info= NULL;
#else
      KEYCACHE_DBUG_ASSERT(0);
#endif
      goto restart;
    }
    hash_link->file= *file;
    hash_link->pageno= pageno;
    link_hash(start, hash_link);
  }
  /* Register the request for the page */
  hash_link->requests++;

  return hash_link;
}


/*
  Get a block for the file page requested by a pagecache read/write operation;
  If the page is not in the cache return a free block, if there is none
  return the lru block after saving its buffer if the page is dirty.

  SYNOPSIS

    find_key_block()
      pagecache            pointer to a page cache data structure
      file                handler for the file to read page from
      pageno              number of the page in the file
      init_hits_left      how initialize the block counter for the page
      wrmode              <-> get for writing
      reg_req             Register request to thye page
      page_st        out  {PAGE_READ,PAGE_TO_BE_READ,PAGE_WAIT_TO_BE_READ}

  RETURN VALUE
    Pointer to the found block if successful, 0 - otherwise

  NOTES.
    For the page from file positioned at pageno the function checks whether
    the page is in the key cache specified by the first parameter.
    If this is the case it immediately returns the block.
    If not, the function first chooses  a block for this page. If there is
    no not used blocks in the key cache yet, the function takes the block
    at the very beginning of the warm sub-chain. It saves the page in that
    block if it's dirty before returning the pointer to it.
    The function returns in the page_st parameter the following values:
      PAGE_READ         - if page already in the block,
      PAGE_TO_BE_READ   - if it is to be read yet by the current thread
      WAIT_TO_BE_READ   - if it is to be read by another thread
    If an error occurs THE BLOCK_ERROR bit is set in the block status.
    It might happen that there are no blocks in LRU chain (in warm part) -
    all blocks  are unlinked for some read/write operations. Then the function
    waits until first of this operations links any block back.
*/

static PAGECACHE_BLOCK_LINK *find_key_block(PAGECACHE *pagecache,
                                            PAGECACHE_FILE *file,
                                            maria_page_no_t pageno,
                                            int init_hits_left,
                                            my_bool wrmode,
                                            my_bool reg_req,
                                            int *page_st)
{
  PAGECACHE_HASH_LINK *hash_link;
  PAGECACHE_BLOCK_LINK *block;
  int error= 0;
  int page_status;

  DBUG_ENTER("find_key_block");
  KEYCACHE_THREAD_TRACE("find_key_block:begin");
  DBUG_PRINT("enter", ("fd: %u  pos %lu  wrmode: %lu",
                       (uint) file->file, (ulong) pageno, (uint) wrmode));
  KEYCACHE_DBUG_PRINT("find_key_block", ("fd: %u  pos: %lu  wrmode: %lu",
                                         (uint) file->file, (ulong) pageno,
                                         (uint) wrmode));
#if !defined(DBUG_OFF) && defined(EXTRA_DEBUG)
  DBUG_EXECUTE("check_pagecache",
               test_key_cache(pagecache, "start of find_key_block", 0););
#endif

restart:
  /* Find the hash link for the requested page (file, pageno) */
  hash_link= get_hash_link(pagecache, file, pageno);

  page_status= -1;
  if ((block= hash_link->block) &&
      block->hash_link == hash_link && (block->status & BLOCK_READ))
    page_status= PAGE_READ;

  if (wrmode && pagecache->resize_in_flush)
  {
    /* This is a write request during the flush phase of a resize operation */

    if (page_status != PAGE_READ)
    {
      /* We don't need the page in the cache: we are going to write on disk */
      hash_link->requests--;
      unlink_hash(pagecache, hash_link);
      return 0;
    }
    if (!(block->status & BLOCK_IN_FLUSH))
    {
      hash_link->requests--;
      /*
        Remove block to invalidate the page in the block buffer
        as we are going to write directly on disk.
        Although we have an exclusive lock for the updated key part
        the control can be yielded by the current thread as we might
        have unfinished readers of other key parts in the block
        buffer. Still we are guaranteed not to have any readers
        of the key part we are writing into until the block is
        removed from the cache as we set the BLOCK_REASSIGNED
        flag (see the code below that handles reading requests).
      */
      free_block(pagecache, block);
      return 0;
    }
    /* Wait until the page is flushed on disk */
    hash_link->requests--;
    {
#ifdef THREAD
      struct st_my_thread_var *thread= my_thread_var;
      add_to_queue(&block->wqueue[COND_FOR_SAVED], thread);
      do
      {
        KEYCACHE_DBUG_PRINT("find_key_block: wait",
                            ("suspend thread %ld", thread->id));
        pagecache_pthread_cond_wait(&thread->suspend,
                                   &pagecache->cache_lock);
      }
      while(thread->next);
#else
      KEYCACHE_DBUG_ASSERT(0);
      /*
        Given the use of "resize_in_flush", it seems impossible
        that this whole branch is ever entered in single-threaded case
        because "(wrmode && pagecache->resize_in_flush)" cannot be true.
        TODO: Check this, and then put the whole branch into the
        "#ifdef THREAD" guard.
      */
#endif
    }
    /* Invalidate page in the block if it has not been done yet */
    if (block->status)
      free_block(pagecache, block);
    return 0;
  }

  if (page_status == PAGE_READ &&
      (block->status & (BLOCK_IN_SWITCH | BLOCK_REASSIGNED)))
  {
    /* This is a request for a page to be removed from cache */

    KEYCACHE_DBUG_PRINT("find_key_block",
                        ("request for old page in block %u "
                         "wrmode: %d  block->status: %d",
                         BLOCK_NUMBER(pagecache, block), wrmode,
                         block->status));
    /*
       Only reading requests can proceed until the old dirty page is flushed,
       all others are to be suspended, then resubmitted
    */
    if (!wrmode && !(block->status & BLOCK_REASSIGNED))
    {
      if (reg_req)
        reg_requests(pagecache, block, 1);
    }
    else
    {
      hash_link->requests--;
      KEYCACHE_DBUG_PRINT("find_key_block",
                          ("request waiting for old page to be saved"));
      {
#ifdef THREAD
        struct st_my_thread_var *thread= my_thread_var;
        /* Put the request into the queue of those waiting for the old page */
        add_to_queue(&block->wqueue[COND_FOR_SAVED], thread);
        /* Wait until the request can be resubmitted */
        do
        {
          KEYCACHE_DBUG_PRINT("find_key_block: wait",
                              ("suspend thread %ld", thread->id));
          pagecache_pthread_cond_wait(&thread->suspend,
                                     &pagecache->cache_lock);
        }
        while(thread->next);
#else
        KEYCACHE_DBUG_ASSERT(0);
          /* No parallel requests in single-threaded case */
#endif
      }
      KEYCACHE_DBUG_PRINT("find_key_block",
                          ("request for old page resubmitted"));
      /* Resubmit the request */
      goto restart;
    }
  }
  else
  {
    /* This is a request for a new page or for a page not to be removed */
    if (! block)
    {
      /* No block is assigned for the page yet */
      if (pagecache->blocks_unused)
      {
        if (pagecache->free_block_list)
        {
          /* There is a block in the free list. */
          block= pagecache->free_block_list;
          pagecache->free_block_list= block->next_used;
          block->next_used= NULL;
        }
        else
        {
          /* There are some never used blocks, take first of them */
          block= &pagecache->block_root[pagecache->blocks_used];
          block->buffer= ADD_TO_PTR(pagecache->block_mem,
                                    ((ulong) pagecache->blocks_used*
                                     pagecache->block_size),
                                    byte*);
          pagecache->blocks_used++;
        }
        pagecache->blocks_unused--;
        DBUG_ASSERT((block->status & BLOCK_WRLOCK) == 0);
        block->status= 0;
#ifndef DBUG_OFF
        block->type= PAGECACHE_EMPTY_PAGE;
#endif
        block->requests= 1;
        block->temperature= BLOCK_COLD;
        block->hits_left= init_hits_left;
        block->last_hit_time= 0;
        link_to_file_list(pagecache, block, file, 0);
        block->hash_link= hash_link;
        hash_link->block= block;
        page_status= PAGE_TO_BE_READ;
        KEYCACHE_DBUG_PRINT("find_key_block",
                            ("got free or never used block %u",
                             BLOCK_NUMBER(pagecache, block)));
      }
      else
      {
	/* There are no never used blocks, use a block from the LRU chain */

        /*
          Wait until a new block is added to the LRU chain;
          several threads might wait here for the same page,
          all of them must get the same block
        */

#ifdef THREAD
        if (! pagecache->used_last)
        {
          struct st_my_thread_var *thread= my_thread_var;
          thread->opt_info= (void *) hash_link;
          link_into_queue(&pagecache->waiting_for_block, thread);
          do
          {
            KEYCACHE_DBUG_PRINT("find_key_block: wait",
                                ("suspend thread %ld", thread->id));
            pagecache_pthread_cond_wait(&thread->suspend,
                                       &pagecache->cache_lock);
          }
          while (thread->next);
          thread->opt_info= NULL;
        }
#else
        KEYCACHE_DBUG_ASSERT(pagecache->used_last);
#endif
        block= hash_link->block;
        if (! block)
        {
          /*
             Take the first block from the LRU chain
             unlinking it from the chain
          */
          block= pagecache->used_last->next_used;
          block->hits_left= init_hits_left;
          block->last_hit_time= 0;
	  if (reg_req)
	    reg_requests(pagecache, block,1);
          hash_link->block= block;
        }
        else
        {
          DBUG_ASSERT((block->status & BLOCK_WRLOCK) == 0);
        }

        if (block->hash_link != hash_link &&
	    ! (block->status & BLOCK_IN_SWITCH) )
        {
	  /* this is a primary request for a new page */
          DBUG_ASSERT((block->status & BLOCK_WRLOCK) == 0);
          block->status|= (BLOCK_IN_SWITCH | BLOCK_WRLOCK);

          KEYCACHE_DBUG_PRINT("find_key_block",
                              ("got block %u for new page",
                               BLOCK_NUMBER(pagecache, block)));

          if (block->status & BLOCK_CHANGED)
          {
	    /* The block contains a dirty page - push it out of the cache */

            KEYCACHE_DBUG_PRINT("find_key_block", ("block is dirty"));

            pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
            /*
	      The call is thread safe because only the current
	      thread might change the block->hash_link value
            */
            DBUG_ASSERT(block->pins == 0);
            error= pagecache_fwrite(pagecache,
                                    &block->hash_link->file,
                                    block->buffer,
                                    block->hash_link->pageno,
                                    block->type,
                                    MYF(MY_NABP | MY_WAIT_IF_FULL));
            pagecache_pthread_mutex_lock(&pagecache->cache_lock);
	    pagecache->global_cache_write++;
          }

          block->status|= BLOCK_REASSIGNED;
          if (block->hash_link)
          {
            /*
	      Wait until all pending read requests
	      for this page are executed
	      (we could have avoided this waiting, if we had read
	      a page in the cache in a sweep, without yielding control)
            */
            wait_for_readers(pagecache, block);

            /* Remove the hash link for this page from the hash table */
            unlink_hash(pagecache, block->hash_link);
            /* All pending requests for this page must be resubmitted */
            if (block->wqueue[COND_FOR_SAVED].last_thread)
              release_queue(&block->wqueue[COND_FOR_SAVED]);
          }
          link_to_file_list(pagecache, block, file,
                            (my_bool)(block->hash_link ? 1 : 0));
          BLOCK_INFO(block);
          block->status= error? BLOCK_ERROR : 0;
#ifndef DBUG_OFF
          block->type= PAGECACHE_EMPTY_PAGE;
#endif
          block->hash_link= hash_link;
          page_status= PAGE_TO_BE_READ;

          KEYCACHE_DBUG_ASSERT(block->hash_link->block == block);
          KEYCACHE_DBUG_ASSERT(hash_link->block->hash_link == hash_link);
        }
        else
        {
          /* This is for secondary requests for a new page only */
          KEYCACHE_DBUG_PRINT("find_key_block",
                              ("block->hash_link: %p  hash_link: %p  "
                               "block->status: %u", block->hash_link,
                               hash_link, block->status ));
          page_status= (((block->hash_link == hash_link) &&
                         (block->status & BLOCK_READ)) ?
                        PAGE_READ : PAGE_WAIT_TO_BE_READ);
        }
      }
      pagecache->global_cache_read++;
    }
    else
    {
      if (reg_req)
	reg_requests(pagecache, block, 1);
      KEYCACHE_DBUG_PRINT("find_key_block",
                          ("block->hash_link: %p  hash_link: %p  "
                           "block->status: %u", block->hash_link,
                           hash_link, block->status ));
      page_status= (((block->hash_link == hash_link) &&
                     (block->status & BLOCK_READ)) ?
                    PAGE_READ : PAGE_WAIT_TO_BE_READ);
    }
  }

  KEYCACHE_DBUG_ASSERT(page_status != -1);
  *page_st=page_status;
  DBUG_PRINT("info",
             ("block: 0x%lx fd: %u  pos %lu  block->status %u page_status %lu",
              (ulong) block, (uint) file->file,
              (ulong) pageno, block->status, (uint) page_status));
  KEYCACHE_DBUG_PRINT("find_key_block",
                      ("block: 0x%lx fd: %u  pos %lu  block->status %u  page_status %lu",
                       (ulong) block,
                       (uint) file->file, (ulong) pageno, block->status,
                       (uint) page_status));

#if !defined(DBUG_OFF) && defined(EXTRA_DEBUG)
  DBUG_EXECUTE("check_pagecache",
               test_key_cache(pagecache, "end of find_key_block",0););
#endif
  KEYCACHE_THREAD_TRACE("find_key_block:end");
  DBUG_RETURN(block);
}


void pagecache_add_pin(PAGECACHE_BLOCK_LINK *block)
{
  DBUG_ENTER("pagecache_add_pin");
  DBUG_PRINT("enter", ("block 0x%lx pins: %u",
                       (ulong) block,
                       block->pins));
  BLOCK_INFO(block);
  block->pins++;
#ifdef PAGECACHE_DEBUG
  {
    PAGECACHE_PIN_INFO *info=
      (PAGECACHE_PIN_INFO *)my_malloc(sizeof(PAGECACHE_PIN_INFO), MYF(0));
    info->thread= my_thread_var;
    info_link(&block->pin_list, info);
  }
#endif
  DBUG_VOID_RETURN;
}

void pagecache_remove_pin(PAGECACHE_BLOCK_LINK *block)
{
  DBUG_ENTER("pagecache_remove_pin");
  DBUG_PRINT("enter", ("block 0x%lx pins: %u",
                       (ulong) block,
                       block->pins));
  BLOCK_INFO(block);
  DBUG_ASSERT(block->pins > 0);
  block->pins--;
#ifdef PAGECACHE_DEBUG
  {
    PAGECACHE_PIN_INFO *info= info_find(block->pin_list, my_thread_var);
    DBUG_ASSERT(info != 0);
    info_unlink(info);
    my_free((gptr) info, MYF(0));
  }
#endif
  DBUG_VOID_RETURN;
}
#ifdef PAGECACHE_DEBUG
void pagecache_add_lock(PAGECACHE_BLOCK_LINK *block, my_bool wl)
{
  PAGECACHE_LOCK_INFO *info=
    (PAGECACHE_LOCK_INFO *)my_malloc(sizeof(PAGECACHE_LOCK_INFO), MYF(0));
  info->thread= my_thread_var;
  info->write_lock= wl;
  info_link((PAGECACHE_PIN_INFO **)&block->lock_list,
	    (PAGECACHE_PIN_INFO *)info);
}
void pagecache_remove_lock(PAGECACHE_BLOCK_LINK *block)
{
  PAGECACHE_LOCK_INFO *info=
    (PAGECACHE_LOCK_INFO *)info_find((PAGECACHE_PIN_INFO *)block->lock_list,
                                     my_thread_var);
  DBUG_ASSERT(info != 0);
  info_unlink((PAGECACHE_PIN_INFO *)info);
  my_free((gptr)info, MYF(0));
}
void pagecache_change_lock(PAGECACHE_BLOCK_LINK *block, my_bool wl)
{
  PAGECACHE_LOCK_INFO *info=
    (PAGECACHE_LOCK_INFO *)info_find((PAGECACHE_PIN_INFO *)block->lock_list,
                                     my_thread_var);
  DBUG_ASSERT(info != 0 && info->write_lock != wl);
  info->write_lock= wl;
}
#else
#define pagecache_add_lock(B,W)
#define pagecache_remove_lock(B)
#define pagecache_change_lock(B,W)
#endif

/*
  Put on the block "update" type lock

  SYNOPSIS
    pagecache_lock_block()
    pagecache            pointer to a page cache data structure
    block                the block to work with

  RETURN
    0 - OK
    1 - Try to lock the block failed
*/

my_bool pagecache_lock_block(PAGECACHE *pagecache,
                             PAGECACHE_BLOCK_LINK *block)
{
  DBUG_ENTER("pagecache_lock_block");
  BLOCK_INFO(block);
  while (block->status & BLOCK_WRLOCK)
  {
    DBUG_PRINT("info", ("fail to lock, waiting..."));
    /* Lock failed we will wait */
#ifdef THREAD
    struct st_my_thread_var *thread= my_thread_var;
    add_to_queue(&block->wqueue[COND_FOR_WRLOCK], thread);
    dec_counter_for_resize_op(pagecache);
    do
    {
      KEYCACHE_DBUG_PRINT("pagecache_lock_block: wait",
                          ("suspend thread %ld", thread->id));
      pagecache_pthread_cond_wait(&thread->suspend,
                                  &pagecache->cache_lock);
    }
    while(thread->next);
#else
    DBUG_ASSERT(0);
#endif
    BLOCK_INFO(block);
    DBUG_RETURN(1);
  }
  /* we are doing it by global cache mutex protectio, so it is OK */
  block->status|= BLOCK_WRLOCK;
  DBUG_PRINT("info", ("WR lock set, block 0x%lx", (ulong)block));
  DBUG_RETURN(0);
}

void pagecache_unlock_block(PAGECACHE_BLOCK_LINK *block)
{
  DBUG_ENTER("pagecache_unlock_block");
  BLOCK_INFO(block);
  DBUG_ASSERT(block->status & BLOCK_WRLOCK);
  block->status&= ~BLOCK_WRLOCK;
  DBUG_PRINT("info", ("WR lock reset, block 0x%lx", (ulong)block));
#ifdef THREAD
  /* release all threads waiting for write lock */
  if (block->wqueue[COND_FOR_WRLOCK].last_thread)
    release_queue(&block->wqueue[COND_FOR_WRLOCK]);
#endif
  BLOCK_INFO(block);
  DBUG_VOID_RETURN;
}

/*
  Try to lock/uplock and pin/unpin the block

  SYNOPSIS
    pagecache_make_lock_and_pin()
    pagecache            pointer to a page cache data structure
    block                the block to work with
    lock                 lock change mode
    pin                  pinchange mode

  RETURN
    0 - OK
    1 - Try to lock the block failed
*/

my_bool pagecache_make_lock_and_pin(PAGECACHE *pagecache,
                                    PAGECACHE_BLOCK_LINK *block,
                                    enum pagecache_page_lock lock,
                                    enum pagecache_page_pin pin)
{
  DBUG_ENTER("pagecache_make_lock_and_pin");
  DBUG_PRINT("enter", ("block: 0x%lx (%u), wrlock: %c pins: %u, lock %s, pin: %s",
                       (ulong)block, BLOCK_NUMBER(pagecache, block),
                       ((block->status & BLOCK_WRLOCK)?'Y':'N'),
                       block->pins,
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin]));
  BLOCK_INFO(block);
#ifdef PAGECACHE_DEBUG
  DBUG_ASSERT(info_check_pin(block, pin) == 0 &&
              info_check_lock(block, lock, pin) == 0);
#endif
  switch (lock)
  {
  case PAGECACHE_LOCK_WRITE:               /* free  -> write */
    /* Writelock and pin the buffer */
    if (pagecache_lock_block(pagecache, block))
    {
      DBUG_PRINT("info", ("restart"));
      /* in case of fail pagecache_lock_block unlock cache */
      DBUG_RETURN(1);
    }
    /* The cache is locked so nothing afraid off */
    pagecache_add_pin(block);
    pagecache_add_lock(block, 1);
    break;
  case PAGECACHE_LOCK_WRITE_TO_READ:       /* write -> read  */
  case PAGECACHE_LOCK_WRITE_UNLOCK:        /* write -> free  */
    /*
      Removes writelog and puts read lock (which is nothing in our
      implementation)
    */
    pagecache_unlock_block(block);
  case PAGECACHE_LOCK_READ_UNLOCK:         /* read  -> free  */
  case PAGECACHE_LOCK_LEFT_READLOCKED:     /* read  -> read  */
#ifndef DBUG_OFF
    if (pin == PAGECACHE_UNPIN)
    {
      pagecache_remove_pin(block);
    }
#endif
#ifdef PAGECACHE_DEBUG
    if (lock == PAGECACHE_LOCK_WRITE_TO_READ)
    {
      pagecache_change_lock(block, 0);
    }
    else if (lock == PAGECACHE_LOCK_WRITE_UNLOCK ||
             lock == PAGECACHE_LOCK_READ_UNLOCK)
    {
      pagecache_remove_lock(block);
    }
#endif
    break;
  case PAGECACHE_LOCK_READ:                /* free  -> read  */
#ifndef DBUG_OFF
    if (pin == PAGECACHE_PIN)
    {
      /* The cache is locked so nothing afraid off */
      pagecache_add_pin(block);
    }
    pagecache_add_lock(block, 0);
    break;
#endif
  case PAGECACHE_LOCK_LEFT_UNLOCKED:       /* free  -> free  */
  case PAGECACHE_LOCK_LEFT_WRITELOCKED:    /* write -> write */
    break; /* do nothing */
  default:
    DBUG_ASSERT(0); /* Never should happened */
  }

  BLOCK_INFO(block);
  DBUG_RETURN(0);
}


/*
  Read into a key cache block buffer from disk.

  SYNOPSIS

    read_block()
      pagecache           pointer to a page cache data structure
      block               block to which buffer the data is to be read
      primary             <-> the current thread will read the data

  RETURN VALUE
    None

  NOTES.
    The function either reads a page data from file to the block buffer,
    or waits until another thread reads it. What page to read is determined
    by a block parameter - reference to a hash link for this page.
    If an error occurs THE BLOCK_ERROR bit is set in the block status.
*/

static void read_block(PAGECACHE *pagecache,
                       PAGECACHE_BLOCK_LINK *block,
                       my_bool primary)
{
  uint got_length;

  /* On entry cache_lock is locked */

  KEYCACHE_THREAD_TRACE("read_block");
  if (primary)
  {
    /*
      This code is executed only by threads
      that submitted primary requests
    */

    KEYCACHE_DBUG_PRINT("read_block",
                        ("page to be read by primary request"));

    /* Page is not in buffer yet, is to be read from disk */
    pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
    /*
      Here other threads may step in and register as secondary readers.
      They will register in block->wqueue[COND_FOR_REQUESTED].
    */
    got_length= pagecache_fread(pagecache, &block->hash_link->file,
                                block->buffer,
                                block->hash_link->pageno, MYF(0));
    pagecache_pthread_mutex_lock(&pagecache->cache_lock);
    if (got_length < pagecache->block_size)
      block->status|= BLOCK_ERROR;
    else
      block->status= (BLOCK_READ | (block->status & BLOCK_WRLOCK));

    KEYCACHE_DBUG_PRINT("read_block",
                        ("primary request: new page in cache"));
    /* Signal that all pending requests for this page now can be processed */
    if (block->wqueue[COND_FOR_REQUESTED].last_thread)
      release_queue(&block->wqueue[COND_FOR_REQUESTED]);
  }
  else
  {
    /*
      This code is executed only by threads
      that submitted secondary requests
    */
    KEYCACHE_DBUG_PRINT("read_block",
                      ("secondary request waiting for new page to be read"));
    {
#ifdef THREAD
      struct st_my_thread_var *thread= my_thread_var;
      /* Put the request into a queue and wait until it can be processed */
      add_to_queue(&block->wqueue[COND_FOR_REQUESTED], thread);
      do
      {
        KEYCACHE_DBUG_PRINT("read_block: wait",
                            ("suspend thread %ld", thread->id));
        pagecache_pthread_cond_wait(&thread->suspend,
                                   &pagecache->cache_lock);
      }
      while (thread->next);
#else
      KEYCACHE_DBUG_ASSERT(0);
      /* No parallel requests in single-threaded case */
#endif
    }
    KEYCACHE_DBUG_PRINT("read_block",
                        ("secondary request: new page in cache"));
  }
}


/*
  Unlock/unpin page and put LSN stamp if it need

  SYNOPSIS
    pagecache_unlock_page()
    pagecache           pointer to a page cache data structure
    file                handler for the file for the block of data to be read
    pageno              number of the block of data in the file
    lock                lock change
    pin                 pin page
    stamp_this_page     put LSN stamp on the page
    first_REDO_LSN_for_page
*/

void pagecache_unlock_page(PAGECACHE *pagecache,
                           PAGECACHE_FILE *file,
                           maria_page_no_t pageno,
                           enum pagecache_page_lock lock,
                           enum pagecache_page_pin pin,
                           my_bool stamp_this_page,
                           LSN first_REDO_LSN_for_page)
{
  PAGECACHE_BLOCK_LINK *block;
  int page_st;
  DBUG_ENTER("pagecache_unlock_page");
  DBUG_PRINT("enter", ("fd: %u  page: %lu l%s p%s",
                       (uint) file->file, (ulong) pageno,
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin]));
  /* we do not allow any lock/pin increasing here */
  DBUG_ASSERT(pin != PAGECACHE_PIN &&
              lock != PAGECACHE_LOCK_READ &&
              lock != PAGECACHE_LOCK_WRITE);
  if (pin == PAGECACHE_PIN_LEFT_UNPINNED &&
      lock == PAGECACHE_LOCK_READ_UNLOCK)
  {
#ifndef DBUG_OFF
    if (
#endif
        /* block do not need here so we do not provide it */
        pagecache_make_lock_and_pin(pagecache, 0, lock, pin)
#ifndef DBUG_OFF
       )
    {
      DBUG_ASSERT(0); /* should not happend */
    }
#else
    ;
#endif
    DBUG_VOID_RETURN;
  }

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  /*
    As soon as we keep lock cache can be used, and we have lock because want
    to unlock.
  */
  DBUG_ASSERT(pagecache->can_be_used);

  inc_counter_for_resize_op(pagecache);
  block= find_key_block(pagecache, file, pageno, 0, 0, 0, &page_st);
  BLOCK_INFO(block);
  DBUG_ASSERT(block != 0 && page_st == PAGE_READ);
  if (stamp_this_page)
  {
    DBUG_ASSERT(lock == PAGECACHE_LOCK_WRITE_UNLOCK &&
                pin == PAGECACHE_UNPIN);
    /* TODO: insert LSN writing code */
  }

#ifndef DBUG_OFF
  if (
#endif
      pagecache_make_lock_and_pin(pagecache, block, lock, pin)
#ifndef DBUG_OFF
     )
  {
    DBUG_ASSERT(0); /* should not happend */
  }
#else
  ;
#endif

  remove_reader(block);
  /*
    Link the block into the LRU chain if it's the last submitted request
    for the block and block will not be pinned
  */
  if (pin != PAGECACHE_PIN_LEFT_PINNED)
    unreg_request(pagecache, block, 1);

  dec_counter_for_resize_op(pagecache);

  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

  DBUG_VOID_RETURN;
}


/*
  Unpin page

  SYNOPSIS
    pagecache_unpin_page()
    pagecache           pointer to a page cache data structure
    file                handler for the file for the block of data to be read
    pageno              number of the block of data in the file
*/

void pagecache_unpin_page(PAGECACHE *pagecache,
                          PAGECACHE_FILE *file,
                          maria_page_no_t pageno)
{
  PAGECACHE_BLOCK_LINK *block;
  int page_st;
  DBUG_ENTER("pagecache_unpin_page");
  DBUG_PRINT("enter", ("fd: %u  page: %lu",
                       (uint) file->file, (ulong) pageno));

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  /*
    As soon as we keep lock cache can be used, and we have lock bacause want
    aunlock.
  */
  DBUG_ASSERT(pagecache->can_be_used);

  inc_counter_for_resize_op(pagecache);
  block= find_key_block(pagecache, file, pageno, 0, 0, 0, &page_st);
  DBUG_ASSERT(block != 0 && page_st == PAGE_READ);

#ifndef DBUG_OFF
  if (
#endif
      /*
        we can just unpin only with keeping read lock because:
        a) we can't pin without any lock
        b) we can't unpin keeping write lock
      */
      pagecache_make_lock_and_pin(pagecache, block,
                                  PAGECACHE_LOCK_LEFT_READLOCKED,
                                  PAGECACHE_UNPIN)
#ifndef DBUG_OFF
     )
  {
    DBUG_ASSERT(0); /* should not happend */
  }
#else
  ;
#endif

  remove_reader(block);
  /*
    Link the block into the LRU chain if it's the last submitted request
    for the block and block will not be pinned
  */
  unreg_request(pagecache, block, 1);

  dec_counter_for_resize_op(pagecache);

  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

  DBUG_VOID_RETURN;
}


/*
  Unlock/unpin page and put LSN stamp if it need
  (uses direct block/page pointer)

  SYNOPSIS
    pagecache_unlock()
    pagecache           pointer to a page cache data structure
    link                direct link to page (returned by read or write)
    lock                lock change
    pin                 pin page
    stamp_this_page     put LSN stamp on the page
    first_REDO_LSN_for_page
*/

void pagecache_unlock(PAGECACHE *pagecache,
                      PAGECACHE_PAGE_LINK *link,
                      enum pagecache_page_lock lock,
                      enum pagecache_page_pin pin,
                      my_bool stamp_this_page,
                      LSN first_REDO_LSN_for_page)
{
  PAGECACHE_BLOCK_LINK *block= (PAGECACHE_BLOCK_LINK *)link;
  DBUG_ENTER("pagecache_unlock");
  DBUG_PRINT("enter", ("block: 0x%lx fd: %u  page: %lu l%s p%s",
                       (ulong) block,
                       (uint) block->hash_link->file.file,
                       (ulong) block->hash_link->pageno,
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin]));
  /* we do not allow any lock/pin increasing here */
  DBUG_ASSERT(pin != PAGECACHE_PIN &&
              lock != PAGECACHE_LOCK_READ &&
              lock != PAGECACHE_LOCK_WRITE);
  if (pin == PAGECACHE_PIN_LEFT_UNPINNED &&
      lock == PAGECACHE_LOCK_READ_UNLOCK)
  {
#ifndef DBUG_OFF
    if (
#endif
        /* block do not need here so we do not provide it */
        pagecache_make_lock_and_pin(pagecache, 0, lock, pin)
#ifndef DBUG_OFF
       )
    {
      DBUG_ASSERT(0); /* should not happend */
    }
#else
    ;
#endif
    DBUG_VOID_RETURN;
  }

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  /*
    As soon as we keep lock cache can be used, and we have lock bacause want
    aunlock.
  */
  DBUG_ASSERT(pagecache->can_be_used);

  inc_counter_for_resize_op(pagecache);
  if (stamp_this_page)
  {
    DBUG_ASSERT(lock == PAGECACHE_LOCK_WRITE_UNLOCK &&
                pin == PAGECACHE_UNPIN);
    /* TODO: insert LSN writing code */
  }

#ifndef DBUG_OFF
  if (
#endif
      pagecache_make_lock_and_pin(pagecache, block, lock, pin)
#ifndef DBUG_OFF
     )
  {
    DBUG_ASSERT(0); /* should not happend */
  }
#else
  ;
#endif

  remove_reader(block);
  /*
    Link the block into the LRU chain if it's the last submitted request
    for the block and block will not be pinned
  */
  if (pin != PAGECACHE_PIN_LEFT_PINNED)
    unreg_request(pagecache, block, 1);

  dec_counter_for_resize_op(pagecache);

  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

  DBUG_VOID_RETURN;
}


/*
  Unpin page
  (uses direct block/page pointer)

  SYNOPSIS
    pagecache_unpin_page()
    pagecache           pointer to a page cache data structure
    link                direct link to page (returned by read or write)
*/

void pagecache_unpin(PAGECACHE *pagecache,
                     PAGECACHE_PAGE_LINK *link)
{
  PAGECACHE_BLOCK_LINK *block= (PAGECACHE_BLOCK_LINK *)link;
  DBUG_ENTER("pagecache_unpin");
  DBUG_PRINT("enter", ("block: 0x%lx fd: %u page: %lu",
                       (ulong) block,
                       (uint) block->hash_link->file.file,
                       (ulong) block->hash_link->pageno));

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  /*
    As soon as we keep lock cache can be used, and we have lock bacause want
    aunlock.
  */
  DBUG_ASSERT(pagecache->can_be_used);

  inc_counter_for_resize_op(pagecache);

#ifndef DBUG_OFF
  if (
#endif
      /*
        we can just unpin only with keeping read lock because:
        a) we can't pin without any lock
        b) we can't unpin keeping write lock
      */
      pagecache_make_lock_and_pin(pagecache, block,
                                  PAGECACHE_LOCK_LEFT_READLOCKED,
                                  PAGECACHE_UNPIN)
#ifndef DBUG_OFF
     )
  {
    DBUG_ASSERT(0); /* should not happend */
  }
#else
  ;
#endif

  remove_reader(block);
  /*
    Link the block into the LRU chain if it's the last submitted request
    for the block and block will not be pinned
  */
  unreg_request(pagecache, block, 1);

  dec_counter_for_resize_op(pagecache);

  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

  DBUG_VOID_RETURN;
}


/*
  Read a block of data from a cached file into a buffer;

  SYNOPSIS
    pagecache_read()
    pagecache           pointer to a page cache data structure
    file                handler for the file for the block of data to be read
    pageno              number of the block of data in the file
    level               determines the weight of the data
    buff                buffer to where the data must be placed
    type                type of the page
    lock                lock change
    link                link to the page if we pin it

  RETURN VALUE
    Returns address from where the data is placed if sucessful, 0 - otherwise.

  NOTES.

    The function ensures that a block of data of size length from file
    positioned at pageno is in the buffers for some key cache blocks.
    Then the function copies the data into the buffer buff.

    Pin will be choosen according to lock parameter (see lock_to_pin)
*/
static enum pagecache_page_pin lock_to_pin[]=
{
  PAGECACHE_PIN_LEFT_UNPINNED /*PAGECACHE_LOCK_LEFT_UNLOCKED*/,
  PAGECACHE_PIN_LEFT_UNPINNED /*PAGECACHE_LOCK_LEFT_READLOCKED*/,
  PAGECACHE_PIN_LEFT_PINNED   /*PAGECACHE_LOCK_LEFT_WRITELOCKED*/,
  PAGECACHE_PIN_LEFT_UNPINNED /*PAGECACHE_LOCK_READ*/,
  PAGECACHE_PIN               /*PAGECACHE_LOCK_WRITE*/,
  PAGECACHE_PIN_LEFT_UNPINNED /*PAGECACHE_LOCK_READ_UNLOCK*/,
  PAGECACHE_UNPIN             /*PAGECACHE_LOCK_WRITE_UNLOCK*/,
  PAGECACHE_UNPIN             /*PAGECACHE_LOCK_WRITE_TO_READ*/
};

byte *pagecache_read(PAGECACHE *pagecache,
                     PAGECACHE_FILE *file,
                     maria_page_no_t pageno,
                     uint level,
                     byte *buff,
                     enum pagecache_page_type type,
                     enum pagecache_page_lock lock,
                     PAGECACHE_PAGE_LINK *link)
{
  int error= 0;
  enum pagecache_page_pin pin= lock_to_pin[lock];
  PAGECACHE_PAGE_LINK fake_link;
  DBUG_ENTER("page_cache_read");
  DBUG_PRINT("enter", ("fd: %u  page: %lu level: %u t:%s l%s p%s",
                       (uint) file->file, (ulong) pageno, level,
                       page_cache_page_type_str[type],
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin]));

  if (!link)
    link= &fake_link;
  else
    *link= 0;

restart:

  if (pagecache->can_be_used)
  {
    /* Key cache is used */
    reg1 PAGECACHE_BLOCK_LINK *block;
    uint status;
    int page_st;

    pagecache_pthread_mutex_lock(&pagecache->cache_lock);
    if (!pagecache->can_be_used)
    {
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      goto no_key_cache;
    }

    inc_counter_for_resize_op(pagecache);
    pagecache->global_cache_r_requests++;
    block= find_key_block(pagecache, file, pageno, level,
                          ((lock == PAGECACHE_LOCK_WRITE) ? 1 : 0),
                          (((pin == PAGECACHE_PIN_LEFT_PINNED) ||
                            (pin == PAGECACHE_UNPIN)) ? 0 : 1),
                          &page_st);
    DBUG_ASSERT(block->type == PAGECACHE_EMPTY_PAGE ||
                block->type == type);
    block->type= type;
    if (pagecache_make_lock_and_pin(pagecache, block, lock, pin))
    {
      /*
        We failed to write lock the block, cache is unlocked, and last write
        lock is released, we will try to get the block again.
      */
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      goto restart;
    }
    if (block->status != BLOCK_ERROR && page_st != PAGE_READ)
    {
      /* The requested page is to be read into the block buffer */
      read_block(pagecache, block,
                 (my_bool)(page_st == PAGE_TO_BE_READ));
    }

    if (! ((status= block->status) & BLOCK_ERROR))
    {
#if !defined(SERIALIZED_READ_FROM_CACHE)
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
#endif

      DBUG_ASSERT((pagecache->block_size & 511) == 0);
      /* Copy data from the cache buffer */
      bmove512(buff, block->buffer, pagecache->block_size);

#if !defined(SERIALIZED_READ_FROM_CACHE)
      pagecache_pthread_mutex_lock(&pagecache->cache_lock);
#endif
    }

    remove_reader(block);
    /*
      Link the block into the LRU chain if it's the last submitted request
      for the block and block will not be pinned
    */
    if (pin != PAGECACHE_PIN_LEFT_PINNED && pin != PAGECACHE_PIN)
      unreg_request(pagecache, block, 1);
    else
      *link= (PAGECACHE_PAGE_LINK)block;

    dec_counter_for_resize_op(pagecache);

    pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

    if (status & BLOCK_ERROR)
      DBUG_RETURN((byte *) 0);

    DBUG_RETURN(buff);
  }

no_key_cache:					/* Key cache is not used */

  /* We can't use mutex here as the key cache may not be initialized */
  pagecache->global_cache_r_requests++;
  pagecache->global_cache_read++;
  if (pagecache_fread(pagecache, file, (byte*) buff, pageno, MYF(MY_NABP)))
    error= 1;
  DBUG_RETURN(error ? (byte*) 0 : buff);
}


/*
  Delete page from the buffer

  SYNOPSIS
    pagecache_delete_page()
    pagecache           pointer to a page cache data structure
    file                handler for the file for the block of data to be read
    pageno              number of the block of data in the file
    lock                lock change
    flush               flush page if it is dirty

  RETURN VALUE
    0 - deleted or was not present at all
    1 - error

  NOTES.
  lock  can be only PAGECACHE_LOCK_LEFT_WRITELOCKED (page was write locked
  before) or PAGECACHE_LOCK_WRITE (delete will write lock page before delete)
*/
my_bool pagecache_delete_page(PAGECACHE *pagecache,
                              PAGECACHE_FILE *file,
                              maria_page_no_t pageno,
                              enum pagecache_page_lock lock,
                              my_bool flush)
{
  int error= 0;
  enum pagecache_page_pin pin= lock_to_pin[lock];
  DBUG_ENTER("pagecache_delete_page");
  DBUG_PRINT("enter", ("fd: %u  page: %lu l%s p%s",
                       (uint) file->file, (ulong) pageno,
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin]));
  DBUG_ASSERT(lock == PAGECACHE_LOCK_WRITE ||
              lock == PAGECACHE_LOCK_LEFT_WRITELOCKED);

restart:

  if (pagecache->can_be_used)
  {
    /* Key cache is used */
    reg1 PAGECACHE_BLOCK_LINK *block;
    PAGECACHE_HASH_LINK **unused_start, *link;

    pagecache_pthread_mutex_lock(&pagecache->cache_lock);
    if (!pagecache->can_be_used)
      goto end;

    inc_counter_for_resize_op(pagecache);
    link= get_present_hash_link(pagecache, file, pageno, &unused_start);
    if (!link)
    {
      DBUG_PRINT("info", ("There is no such page in the cache"));
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      DBUG_RETURN(0);
    }
    block= link->block;
    DBUG_ASSERT(block != 0);
    if (pagecache_make_lock_and_pin(pagecache, block, lock, pin))
    {
      /*
        We failed to writelock the block, cache is unlocked, and last write
        lock is released, we will try to get the block again.
      */
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      goto restart;
    }

    if (block->status & BLOCK_CHANGED && flush)
    {
      /* The block contains a dirty page - push it out of the cache */

      KEYCACHE_DBUG_PRINT("find_key_block", ("block is dirty"));

      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      /*
        The call is thread safe because only the current
        thread might change the block->hash_link value
      */
      DBUG_ASSERT(block->pins == 1);
      error= pagecache_fwrite(pagecache,
                              &block->hash_link->file,
                              block->buffer,
                              block->hash_link->pageno,
                              block->type,
                              MYF(MY_NABP | MY_WAIT_IF_FULL));
      pagecache_pthread_mutex_lock(&pagecache->cache_lock);
      pagecache->global_cache_write++;

      if (error)
      {
        block->status|= BLOCK_ERROR;
        goto err;
      }

      pagecache->blocks_changed--;
      pagecache->global_blocks_changed--;
      /*
        free_block() will change the status of the block so no need to change
        it here.
      */

    }
    /* Cache is locked, so we can relese page before freeing it */
    pagecache_make_lock_and_pin(pagecache, block,
                                PAGECACHE_LOCK_WRITE_UNLOCK,
                                PAGECACHE_UNPIN);
    if (pin == PAGECACHE_PIN_LEFT_PINNED)
      unreg_request(pagecache, block, 1);
    free_block(pagecache, block);

err:
    dec_counter_for_resize_op(pagecache);
end:
    pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
  }

  DBUG_RETURN(error);
}


/*
  Write a buffer into a cached file.

  SYNOPSIS

    pagecache_write()
      pagecache           pointer to a page cache data structure
      file                handler for the file to write data to
      pageno              number of the block of data in the file
      level               determines the weight of the data
      buff                buffer to where the data must be placed
      type                type of the page
      lock                lock change
      pin                 pin page
      write_mode          how to write page
      link                link to the page if we pin it

  RETURN VALUE
    0 if a success, 1 - otherwise.
*/

struct write_lock_change
{
  int need_lock_change;
  enum pagecache_page_lock new_lock;
  enum pagecache_page_lock unlock_lock;
};

static struct write_lock_change write_lock_change_table[]=
{
  {1,
   PAGECACHE_LOCK_WRITE,
   PAGECACHE_LOCK_WRITE_UNLOCK} /*PAGECACHE_LOCK_LEFT_UNLOCKED*/,
  {0, /*unsupported*/
   PAGECACHE_LOCK_LEFT_UNLOCKED,
   PAGECACHE_LOCK_LEFT_UNLOCKED} /*PAGECACHE_LOCK_LEFT_READLOCKED*/,
  {0, PAGECACHE_LOCK_LEFT_WRITELOCKED, 0} /*PAGECACHE_LOCK_LEFT_WRITELOCKED*/,
  {1,
   PAGECACHE_LOCK_WRITE,
   PAGECACHE_LOCK_WRITE_TO_READ} /*PAGECACHE_LOCK_READ*/,
  {0, PAGECACHE_LOCK_WRITE, 0} /*PAGECACHE_LOCK_WRITE*/,
  {0, /*unsupported*/
   PAGECACHE_LOCK_LEFT_UNLOCKED,
   PAGECACHE_LOCK_LEFT_UNLOCKED} /*PAGECACHE_LOCK_READ_UNLOCK*/,
  {1,
   PAGECACHE_LOCK_LEFT_WRITELOCKED,
   PAGECACHE_LOCK_WRITE_UNLOCK } /*PAGECACHE_LOCK_WRITE_UNLOCK*/,
  {1,
   PAGECACHE_LOCK_LEFT_WRITELOCKED,
   PAGECACHE_LOCK_WRITE_TO_READ}/*PAGECACHE_LOCK_WRITE_TO_READ*/
};

struct write_pin_change
{
  enum pagecache_page_pin new_pin;
  enum pagecache_page_pin unlock_pin;
};

static struct write_pin_change write_pin_change_table[]=
{
  {PAGECACHE_PIN_LEFT_PINNED,
   PAGECACHE_PIN_LEFT_PINNED} /*PAGECACHE_PIN_LEFT_PINNED*/,
  {PAGECACHE_PIN,
   PAGECACHE_UNPIN} /*PAGECACHE_PIN_LEFT_UNPINNED*/,
  {PAGECACHE_PIN,
   PAGECACHE_PIN_LEFT_PINNED} /*PAGECACHE_PIN*/,
  {PAGECACHE_PIN_LEFT_PINNED,
   PAGECACHE_UNPIN} /*PAGECACHE_UNPIN*/
};

my_bool pagecache_write(PAGECACHE *pagecache,
                        PAGECACHE_FILE *file,
                        maria_page_no_t pageno,
                        uint level,
                        byte *buff,
                        enum pagecache_page_type type,
                        enum pagecache_page_lock lock,
                        enum pagecache_page_pin pin,
                        enum pagecache_write_mode write_mode,
                        PAGECACHE_PAGE_LINK *link)
{
  reg1 PAGECACHE_BLOCK_LINK *block;
  PAGECACHE_PAGE_LINK fake_link;
  int error= 0;
  int need_lock_change= write_lock_change_table[lock].need_lock_change;
  DBUG_ENTER("pagecache_write");
  DBUG_PRINT("enter", ("fd: %u  page: %lu level: %u t:%s l%s p%s m%s",
                       (uint) file->file, (ulong) pageno, level,
                       page_cache_page_type_str[type],
                       page_cache_page_lock_str[lock],
                       page_cache_page_pin_str[pin],
                       page_cache_page_write_mode_str[write_mode]));
  DBUG_ASSERT(lock != PAGECACHE_LOCK_LEFT_READLOCKED &&
              lock != PAGECACHE_LOCK_READ_UNLOCK);
  if (!link)
    link= &fake_link;
  else
    *link= 0;

  if (write_mode == PAGECACHE_WRITE_NOW)
  {
    /* we allow direct write if wwe do not use long term lockings */
    DBUG_ASSERT(lock == PAGECACHE_LOCK_LEFT_UNLOCKED);
    /* Force writing from buff into disk */
    pagecache->global_cache_write++;
    if (pagecache_fwrite(pagecache, file, buff, pageno, type,
                         MYF(MY_NABP | MY_WAIT_IF_FULL)))
      DBUG_RETURN(1);
  }
restart:

#if !defined(DBUG_OFF) && defined(EXTRA_DEBUG)
  DBUG_EXECUTE("check_pagecache",
               test_key_cache(pagecache, "start of key_cache_write", 1););
#endif

  if (pagecache->can_be_used)
  {
    /* Key cache is used */
    int page_st;

    pagecache_pthread_mutex_lock(&pagecache->cache_lock);
    if (!pagecache->can_be_used)
    {
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      goto no_key_cache;
    }

    inc_counter_for_resize_op(pagecache);
    pagecache->global_cache_w_requests++;
    {
      int need_wrlock= (write_mode != PAGECACHE_WRITE_DONE &&
                        lock != PAGECACHE_LOCK_LEFT_WRITELOCKED &&
                        lock != PAGECACHE_LOCK_WRITE_UNLOCK &&
                        lock != PAGECACHE_LOCK_WRITE_TO_READ);
      block= find_key_block(pagecache, file, pageno, level,
                            (need_wrlock ? 1 : 0),
                            (need_wrlock ? 1 : 0),
                            &page_st);
    }
    if (!block)
    {
      DBUG_ASSERT(write_mode != PAGECACHE_WRITE_DONE);
      /* It happens only for requests submitted during resize operation */
      dec_counter_for_resize_op(pagecache);
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      /* Write to the disk key cache is in resize at the moment*/
      goto no_key_cache;
    }

    DBUG_ASSERT(block->type == PAGECACHE_EMPTY_PAGE ||
                block->type == type);
    block->type= type;

    if (pagecache_make_lock_and_pin(pagecache, block,
                                    write_lock_change_table[lock].new_lock,
                                    (need_lock_change ?
                                     write_pin_change_table[pin].new_pin :
                                     pin)))
    {
      /*
        We failed to writelock the block, cache is unlocked, and last write
        lock is released, we will try to get the block again.
      */
      pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
      goto restart;
    }


    if (write_mode == PAGECACHE_WRITE_DONE)
    {
      if (block->status != BLOCK_ERROR && page_st != PAGE_READ)
      {
        /* Copy data from buff */
        bmove512(block->buffer, buff, pagecache->block_size);
        block->status= (BLOCK_READ | (block->status & BLOCK_WRLOCK));
        KEYCACHE_DBUG_PRINT("key_cache_insert",
                            ("primary request: new page in cache"));
        /* Signal that all pending requests for this now can be processed. */
        if (block->wqueue[COND_FOR_REQUESTED].last_thread)
          release_queue(&block->wqueue[COND_FOR_REQUESTED]);
      }
    }
    else
    {
      if (write_mode == PAGECACHE_WRITE_NOW)
      {
        /* buff has been written to disk at start */
        if (block->status & BLOCK_CHANGED)
          link_to_file_list(pagecache, block, &block->hash_link->file, 1);
      }
      else
      {
        if (! (block->status & BLOCK_CHANGED))
          link_to_changed_list(pagecache, block);
      }
      if (! (block->status & BLOCK_ERROR))
      {
        bmove512(block->buffer, buff, pagecache->block_size);
      }
      block->status|= BLOCK_READ;
    }


    if (need_lock_change)
    {
#ifndef DBUG_OFF
      int rc=
#endif
#warning we are doing an unlock here, so need to give the page its rec_lsn!
        pagecache_make_lock_and_pin(pagecache, block,
                                    write_lock_change_table[lock].unlock_lock,
                                    write_pin_change_table[pin].unlock_pin);
#ifndef DBUG_OFF
      DBUG_ASSERT(rc == 0);
#endif
    }

    /* Unregister the request */

    block->hash_link->requests--;
    if (pin != PAGECACHE_PIN_LEFT_PINNED && pin != PAGECACHE_PIN)
    {
      if (write_mode != PAGECACHE_WRITE_DONE)
      {
        unreg_request(pagecache, block, 1);
      }
    }
    else
      *link= (PAGECACHE_PAGE_LINK)block;


    if (block->status & BLOCK_ERROR)
      error= 1;

    dec_counter_for_resize_op(pagecache);

    pagecache_pthread_mutex_unlock(&pagecache->cache_lock);

    goto end;
  }

no_key_cache:
  /* Key cache is not used */
  if (write_mode == PAGECACHE_WRITE_DELAY)
  {
    pagecache->global_cache_w_requests++;
    pagecache->global_cache_write++;
    if (pagecache_fwrite(pagecache, file, (byte*) buff, pageno, type,
                         MYF(MY_NABP | MY_WAIT_IF_FULL)))
      error=1;
  }

end:
#if !defined(DBUG_OFF) && defined(EXTRA_DEBUG)
  DBUG_EXECUTE("exec",
               test_key_cache(pagecache, "end of key_cache_write", 1););
#endif
  DBUG_RETURN(error);
}


/*
  Free block: remove reference to it from hash table,
  remove it from the chain file of dirty/clean blocks
  and add it to the free list.
*/

static void free_block(PAGECACHE *pagecache, PAGECACHE_BLOCK_LINK *block)
{
  KEYCACHE_THREAD_TRACE("free block");
  KEYCACHE_DBUG_PRINT("free_block",
                      ("block %u to be freed, hash_link %p",
                       BLOCK_NUMBER(pagecache, block), block->hash_link));
  if (block->hash_link)
  {
    /*
      While waiting for readers to finish, new readers might request the
      block. But since we set block->status|= BLOCK_REASSIGNED, they
      will wait on block->wqueue[COND_FOR_SAVED]. They must be signalled
      later.
    */
    block->status|= BLOCK_REASSIGNED;
    wait_for_readers(pagecache, block);
    unlink_hash(pagecache, block->hash_link);
  }

  unlink_changed(block);
  DBUG_ASSERT((block->status & BLOCK_WRLOCK) == 0);
  block->status= 0;
#ifndef DBUG_OFF
  block->type= PAGECACHE_EMPTY_PAGE;
#endif
  KEYCACHE_THREAD_TRACE("free block");
  KEYCACHE_DBUG_PRINT("free_block",
                      ("block is freed"));
  unreg_request(pagecache, block, 0);
  block->hash_link= NULL;

  /* Remove the free block from the LRU ring. */
  unlink_block(pagecache, block);
  if (block->temperature == BLOCK_WARM)
    pagecache->warm_blocks--;
  block->temperature= BLOCK_COLD;
  /* Insert the free block in the free list. */
  block->next_used= pagecache->free_block_list;
  pagecache->free_block_list= block;
  /* Keep track of the number of currently unused blocks. */
  pagecache->blocks_unused++;

  /* All pending requests for this page must be resubmitted. */
  if (block->wqueue[COND_FOR_SAVED].last_thread)
    release_queue(&block->wqueue[COND_FOR_SAVED]);
}


static int cmp_sec_link(PAGECACHE_BLOCK_LINK **a, PAGECACHE_BLOCK_LINK **b)
{
  return (((*a)->hash_link->pageno < (*b)->hash_link->pageno) ? -1 :
      ((*a)->hash_link->pageno > (*b)->hash_link->pageno) ? 1 : 0);
}


/*
  Flush a portion of changed blocks to disk,
  free used blocks if requested
*/

static int flush_cached_blocks(PAGECACHE *pagecache,
                               PAGECACHE_FILE *file,
                               PAGECACHE_BLOCK_LINK **cache,
                               PAGECACHE_BLOCK_LINK **end,
                               enum flush_type type)
{
  int error;
  int last_errno= 0;
  uint count= (uint) (end-cache);
  DBUG_ENTER("flush_cached_blocks");

  /* Don't lock the cache during the flush */
  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
  /*
     As all blocks referred in 'cache' are marked by BLOCK_IN_FLUSH
     we are guarunteed no thread will change them
  */
  qsort((byte*) cache, count, sizeof(*cache), (qsort_cmp) cmp_sec_link);

  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  for (; cache != end; cache++)
  {
    PAGECACHE_BLOCK_LINK *block= *cache;

    if (block->pins)
    {
      KEYCACHE_DBUG_PRINT("flush_cached_blocks",
                          ("block %u (0x%lx) pinned",
                           BLOCK_NUMBER(pagecache, block), (ulong)block));
      DBUG_PRINT("info", ("block %u (0x%lx) pinned",
                          BLOCK_NUMBER(pagecache, block), (ulong)block));
      BLOCK_INFO(block);
      last_errno= -1;
      unreg_request(pagecache, block, 1);
      continue;
    }
    /* if the block is not pinned then it is not write locked */
    DBUG_ASSERT((block->status & BLOCK_WRLOCK) == 0);
#ifndef DBUG_OFF
    {
      int rc=
#endif
    pagecache_make_lock_and_pin(pagecache, block,
                                PAGECACHE_LOCK_WRITE, PAGECACHE_PIN);
#ifndef DBUG_OFF
      DBUG_ASSERT(rc == 0);
    }
#endif

    KEYCACHE_DBUG_PRINT("flush_cached_blocks",
                        ("block %u (0x%lx) to be flushed",
                         BLOCK_NUMBER(pagecache, block), (ulong)block));
    DBUG_PRINT("info", ("block %u (0x%lx) to be flushed",
                        BLOCK_NUMBER(pagecache, block), (ulong)block));
    BLOCK_INFO(block);
    pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
    DBUG_PRINT("info", ("block %u (0x%lx) pins: %u",
                        BLOCK_NUMBER(pagecache, block), (ulong)block,
                        block->pins));
    DBUG_ASSERT(block->pins == 1);
    error= pagecache_fwrite(pagecache, file,
                            block->buffer,
                            block->hash_link->pageno,
                            block->type,
                            MYF(MY_NABP | MY_WAIT_IF_FULL));
    pagecache_pthread_mutex_lock(&pagecache->cache_lock);

    pagecache_make_lock_and_pin(pagecache, block,
                                PAGECACHE_LOCK_WRITE_UNLOCK,
                                PAGECACHE_UNPIN);

    pagecache->global_cache_write++;
    if (error)
    {
      block->status|= BLOCK_ERROR;
      if (!last_errno)
        last_errno= errno ? errno : -1;
    }
    /*
      Let to proceed for possible waiting requests to write to the block page.
      It might happen only during an operation to resize the key cache.
    */
    if (block->wqueue[COND_FOR_SAVED].last_thread)
      release_queue(&block->wqueue[COND_FOR_SAVED]);
    /* type will never be FLUSH_IGNORE_CHANGED here */
    if (! (type == FLUSH_KEEP || type == FLUSH_FORCE_WRITE))
    {
      pagecache->blocks_changed--;
      pagecache->global_blocks_changed--;
      free_block(pagecache, block);
    }
    else
    {
      block->status&= ~BLOCK_IN_FLUSH;
      link_to_file_list(pagecache, block, file, 1);
      unreg_request(pagecache, block, 1);
    }
  }
  DBUG_RETURN(last_errno);
}


/*
  flush all key blocks for a file to disk, but don't do any mutex locks

    flush_pagecache_blocks_int()
      pagecache            pointer to a key cache data structure
      file                handler for the file to flush to
      flush_type          type of the flush

  NOTES
    This function doesn't do any mutex locks because it needs to be called
    both from flush_pagecache_blocks and flush_all_key_blocks (the later one
    does the mutex lock in the resize_pagecache() function).

  RETURN
    0   ok
    1  error
*/

static int flush_pagecache_blocks_int(PAGECACHE *pagecache,
                                      PAGECACHE_FILE *file,
                                      enum flush_type type)
{
  PAGECACHE_BLOCK_LINK *cache_buff[FLUSH_CACHE],**cache;
  int last_errno= 0;
  DBUG_ENTER("flush_pagecache_blocks_int");
  DBUG_PRINT("enter",("file: %d  blocks_used: %d  blocks_changed: %d",
              file->file, pagecache->blocks_used, pagecache->blocks_changed));

#if !defined(DBUG_OFF) && defined(EXTRA_DEBUG)
    DBUG_EXECUTE("check_pagecache",
                 test_key_cache(pagecache,
                                "start of flush_pagecache_blocks", 0););
#endif

  cache= cache_buff;
  if (pagecache->disk_blocks > 0 &&
      (!my_disable_flush_pagecache_blocks || type != FLUSH_KEEP))
  {
    /* Key cache exists and flush is not disabled */
    int error= 0;
    uint count= 0;
    PAGECACHE_BLOCK_LINK **pos, **end;
    PAGECACHE_BLOCK_LINK *first_in_switch= NULL;
    PAGECACHE_BLOCK_LINK *block, *next;
#if defined(PAGECACHE_DEBUG)
    uint cnt= 0;
#endif

    if (type != FLUSH_IGNORE_CHANGED)
    {
      /*
         Count how many key blocks we have to cache to be able
         to flush all dirty pages with minimum seek moves
      */
      for (block= pagecache->changed_blocks[FILE_HASH(*file)] ;
           block;
           block= block->next_changed)
      {
        if (block->hash_link->file.file == file->file)
        {
          count++;
          KEYCACHE_DBUG_ASSERT(count<= pagecache->blocks_used);
        }
      }
      /* Allocate a new buffer only if its bigger than the one we have */
      if (count > FLUSH_CACHE &&
          !(cache=
            (PAGECACHE_BLOCK_LINK**)
            my_malloc(sizeof(PAGECACHE_BLOCK_LINK*)*count, MYF(0))))
      {
        cache= cache_buff;
        count= FLUSH_CACHE;
      }
    }

    /* Retrieve the blocks and write them to a buffer to be flushed */
restart:
    end= (pos= cache)+count;
    for (block= pagecache->changed_blocks[FILE_HASH(*file)] ;
         block;
         block= next)
    {
#if defined(PAGECACHE_DEBUG)
      cnt++;
      KEYCACHE_DBUG_ASSERT(cnt <= pagecache->blocks_used);
#endif
      next= block->next_changed;
      if (block->hash_link->file.file == file->file)
      {
        /*
           Mark the block with BLOCK_IN_FLUSH in order not to let
           other threads to use it for new pages and interfere with
           our sequence ot flushing dirty file pages
        */
        block->status|= BLOCK_IN_FLUSH;

        if (! (block->status & BLOCK_IN_SWITCH))
        {
	  /*
	    We care only for the blocks for which flushing was not
	    initiated by other threads as a result of page swapping
          */
          reg_requests(pagecache, block, 1);
          if (type != FLUSH_IGNORE_CHANGED)
          {
	    /* It's not a temporary file */
            if (pos == end)
            {
	      /*
		This happens only if there is not enough
		memory for the big block
              */
              if ((error= flush_cached_blocks(pagecache, file, cache,
                                              end,type)))
                last_errno=error;
              /*
		Restart the scan as some other thread might have changed
		the changed blocks chain: the blocks that were in switch
		state before the flush started have to be excluded
              */
              goto restart;
            }
            *pos++= block;
          }
          else
          {
            /* It's a temporary file */
            pagecache->blocks_changed--;
	    pagecache->global_blocks_changed--;
            free_block(pagecache, block);
          }
        }
        else
        {
	  /* Link the block into a list of blocks 'in switch' */
#warning this unlink_changed() is a serious problem for Maria's Checkpoint: it \
removes a page from the list of dirty pages, while it's still dirty. A  \
  solution is to abandon first_in_switch, just wait for this page to be \
  flushed by somebody else, and loop. TODO: check all places where we remove a \
  page from the list of dirty pages
          unlink_changed(block);
          link_changed(block, &first_in_switch);
        }
      }
    }
    if (pos != cache)
    {
      if ((error= flush_cached_blocks(pagecache, file, cache, pos, type)))
        last_errno= error;
    }
    /* Wait until list of blocks in switch is empty */
    while (first_in_switch)
    {
#if defined(PAGECACHE_DEBUG)
      cnt= 0;
#endif
      block= first_in_switch;
      {
#ifdef THREAD
        struct st_my_thread_var *thread= my_thread_var;
        add_to_queue(&block->wqueue[COND_FOR_SAVED], thread);
        do
        {
          KEYCACHE_DBUG_PRINT("flush_pagecache_blocks_int: wait",
                              ("suspend thread %ld", thread->id));
          pagecache_pthread_cond_wait(&thread->suspend,
                                     &pagecache->cache_lock);
        }
        while (thread->next);
#else
        KEYCACHE_DBUG_ASSERT(0);
        /* No parallel requests in single-threaded case */
#endif
      }
#if defined(PAGECACHE_DEBUG)
      cnt++;
      KEYCACHE_DBUG_ASSERT(cnt <= pagecache->blocks_used);
#endif
    }
    /* The following happens very seldom */
    if (! (type == FLUSH_KEEP || type == FLUSH_FORCE_WRITE))
    {
#if defined(PAGECACHE_DEBUG)
      cnt=0;
#endif
      for (block= pagecache->file_blocks[FILE_HASH(*file)] ;
           block;
           block= next)
      {
#if defined(PAGECACHE_DEBUG)
        cnt++;
        KEYCACHE_DBUG_ASSERT(cnt <= pagecache->blocks_used);
#endif
        next= block->next_changed;
        if (block->hash_link->file.file == file->file &&
            (! (block->status & BLOCK_CHANGED)
             || type == FLUSH_IGNORE_CHANGED))
        {
          reg_requests(pagecache, block, 1);
          free_block(pagecache, block);
        }
      }
    }
  }

#ifndef DBUG_OFF
  DBUG_EXECUTE("check_pagecache",
               test_key_cache(pagecache, "end of flush_pagecache_blocks", 0););
#endif
  if (cache != cache_buff)
    my_free((gptr) cache, MYF(0));
  if (last_errno)
    errno=last_errno;                /* Return first error */
  DBUG_RETURN(last_errno != 0);
}


/*
  Flush all blocks for a file to disk

  SYNOPSIS

    flush_pagecache_blocks()
      pagecache            pointer to a page cache data structure
      file                handler for the file to flush to
      flush_type          type of the flush

  RETURN
    0   ok
    1  error
*/

int flush_pagecache_blocks(PAGECACHE *pagecache,
                           PAGECACHE_FILE *file, enum flush_type type)
{
  int res;
  DBUG_ENTER("flush_pagecache_blocks");
  DBUG_PRINT("enter", ("pagecache: 0x%lx", pagecache));

  if (pagecache->disk_blocks <= 0)
    DBUG_RETURN(0);
  pagecache_pthread_mutex_lock(&pagecache->cache_lock);
  inc_counter_for_resize_op(pagecache);
  res= flush_pagecache_blocks_int(pagecache, file, type);
  dec_counter_for_resize_op(pagecache);
  pagecache_pthread_mutex_unlock(&pagecache->cache_lock);
  DBUG_RETURN(res);
}


/*
  Flush all blocks in the key cache to disk
*/

static int flush_all_key_blocks(PAGECACHE *pagecache)
{
#if defined(PAGECACHE_DEBUG)
  uint cnt=0;
#endif
  while (pagecache->blocks_changed > 0)
  {
    PAGECACHE_BLOCK_LINK *block;
    for (block= pagecache->used_last->next_used ; ; block=block->next_used)
    {
      if (block->hash_link)
      {
#if defined(PAGECACHE_DEBUG)
        cnt++;
        KEYCACHE_DBUG_ASSERT(cnt <= pagecache->blocks_used);
#endif
        if (flush_pagecache_blocks_int(pagecache, &block->hash_link->file,
                                       FLUSH_RELEASE))
          return 1;
        break;
      }
      if (block == pagecache->used_last)
        break;
    }
  }
  return 0;
}


/*
  Reset the counters of a key cache.

  SYNOPSIS
    reset_key_cache_counters()
    name       the name of a key cache
    key_cache  pointer to the key kache to be reset

  DESCRIPTION
   This procedure is used by process_key_caches() to reset the counters of all
   currently used key caches, both the default one and the named ones.

  RETURN
    0 on success (always because it can't fail)
*/

int reset_key_cache_counters(const char *name, PAGECACHE *key_cache)
{
  DBUG_ENTER("reset_key_cache_counters");
  if (!key_cache->inited)
  {
    DBUG_PRINT("info", ("Key cache %s not initialized.", name));
    DBUG_RETURN(0);
  }
  DBUG_PRINT("info", ("Resetting counters for key cache %s.", name));

  key_cache->global_blocks_changed= 0;   /* Key_blocks_not_flushed */
  key_cache->global_cache_r_requests= 0; /* Key_read_requests */
  key_cache->global_cache_read= 0;       /* Key_reads */
  key_cache->global_cache_w_requests= 0; /* Key_write_requests */
  key_cache->global_cache_write= 0;      /* Key_writes */
  DBUG_RETURN(0);
}


#ifndef DBUG_OFF
/*
  Test if disk-cache is ok
*/
static void test_key_cache(PAGECACHE *pagecache __attribute__((unused)),
                           const char *where __attribute__((unused)),
                           my_bool lock __attribute__((unused)))
{
  /* TODO */
}
#endif

#if defined(PAGECACHE_TIMEOUT)

#define KEYCACHE_DUMP_FILE  "pagecache_dump.txt"
#define MAX_QUEUE_LEN  100


static void pagecache_dump(PAGECACHE *pagecache)
{
  FILE *pagecache_dump_file=fopen(KEYCACHE_DUMP_FILE, "w");
  struct st_my_thread_var *last;
  struct st_my_thread_var *thread;
  PAGECACHE_BLOCK_LINK *block;
  PAGECACHE_HASH_LINK *hash_link;
  PAGECACHE_PAGE *page;
  uint i;

  fprintf(pagecache_dump_file, "thread:%u\n", thread->id);

  i=0;
  thread=last=waiting_for_hash_link.last_thread;
  fprintf(pagecache_dump_file, "queue of threads waiting for hash link\n");
  if (thread)
    do
    {
      thread= thread->next;
      page= (PAGECACHE_PAGE *) thread->opt_info;
      fprintf(pagecache_dump_file,
              "thread:%u, (file,pageno)=(%u,%lu)\n",
              thread->id,(uint) page->file.file,(ulong) page->pageno);
      if (++i == MAX_QUEUE_LEN)
        break;
    }
    while (thread != last);

  i=0;
  thread=last=waiting_for_block.last_thread;
  fprintf(pagecache_dump_file, "queue of threads waiting for block\n");
  if (thread)
    do
    {
      thread=thread->next;
      hash_link= (PAGECACHE_HASH_LINK *) thread->opt_info;
      fprintf(pagecache_dump_file,
        "thread:%u hash_link:%u (file,pageno)=(%u,%lu)\n",
        thread->id, (uint) PAGECACHE_HASH_LINK_NUMBER(pagecache, hash_link),
        (uint) hash_link->file.file,(ulong) hash_link->pageno);
      if (++i == MAX_QUEUE_LEN)
        break;
    }
    while (thread != last);

  for (i=0 ; i < pagecache->blocks_used ; i++)
  {
    int j;
    block= &pagecache->block_root[i];
    hash_link= block->hash_link;
    fprintf(pagecache_dump_file,
            "block:%u hash_link:%d status:%x #requests=%u waiting_for_readers:%d\n",
            i, (int) (hash_link ?
                      PAGECACHE_HASH_LINK_NUMBER(pagecache, hash_link) :
                      -1),
            block->status, block->requests, block->condvar ? 1 : 0);
    for (j=0 ; j < COND_SIZE; j++)
    {
      PAGECACHE_WQUEUE *wqueue=&block->wqueue[j];
      thread= last= wqueue->last_thread;
      fprintf(pagecache_dump_file, "queue #%d\n", j);
      if (thread)
      {
        do
        {
          thread=thread->next;
          fprintf(pagecache_dump_file,
                  "thread:%u\n", thread->id);
          if (++i == MAX_QUEUE_LEN)
            break;
        }
        while (thread != last);
      }
    }
  }
  fprintf(pagecache_dump_file, "LRU chain:");
  block= pagecache= used_last;
  if (block)
  {
    do
    {
      block= block->next_used;
      fprintf(pagecache_dump_file,
              "block:%u, ", BLOCK_NUMBER(pagecache, block));
    }
    while (block != pagecache->used_last);
  }
  fprintf(pagecache_dump_file, "\n");

  fclose(pagecache_dump_file);
}

#endif /* defined(PAGECACHE_TIMEOUT) */

#if defined(PAGECACHE_TIMEOUT) && !defined(__WIN__)


static int pagecache_pthread_cond_wait(pthread_cond_t *cond,
                                      pthread_mutex_t *mutex)
{
  int rc;
  struct timeval  now;            /* time when we started waiting        */
  struct timespec timeout;        /* timeout value for the wait function */
  struct timezone tz;
#if defined(PAGECACHE_DEBUG)
  int cnt=0;
#endif

  /* Get current time */
  gettimeofday(&now, &tz);
  /* Prepare timeout value */
  timeout.tv_sec= now.tv_sec + PAGECACHE_TIMEOUT;
 /*
   timeval uses microseconds.
   timespec uses nanoseconds.
   1 nanosecond = 1000 micro seconds
 */
  timeout.tv_nsec= now.tv_usec * 1000;
  KEYCACHE_THREAD_TRACE_END("started waiting");
#if defined(PAGECACHE_DEBUG)
  cnt++;
  if (cnt % 100 == 0)
    fprintf(pagecache_debug_log, "waiting...\n");
    fflush(pagecache_debug_log);
#endif
  rc= pthread_cond_timedwait(cond, mutex, &timeout);
  KEYCACHE_THREAD_TRACE_BEGIN("finished waiting");
  if (rc == ETIMEDOUT || rc == ETIME)
  {
#if defined(PAGECACHE_DEBUG)
    fprintf(pagecache_debug_log,"aborted by pagecache timeout\n");
    fclose(pagecache_debug_log);
    abort();
#endif
    pagecache_dump();
  }

#if defined(PAGECACHE_DEBUG)
  KEYCACHE_DBUG_ASSERT(rc != ETIMEDOUT);
#else
  assert(rc != ETIMEDOUT);
#endif
  return rc;
}
#else
#if defined(PAGECACHE_DEBUG)
static int pagecache_pthread_cond_wait(pthread_cond_t *cond,
                                      pthread_mutex_t *mutex)
{
  int rc;
  KEYCACHE_THREAD_TRACE_END("started waiting");
  rc= pthread_cond_wait(cond, mutex);
  KEYCACHE_THREAD_TRACE_BEGIN("finished waiting");
  return rc;
}
#endif
#endif /* defined(PAGECACHE_TIMEOUT) && !defined(__WIN__) */

#if defined(PAGECACHE_DEBUG) 
static int ___pagecache_pthread_mutex_lock(pthread_mutex_t *mutex)
{
  int rc;
  rc= pthread_mutex_lock(mutex);
  KEYCACHE_THREAD_TRACE_BEGIN("");
  return rc;
}


static void ___pagecache_pthread_mutex_unlock(pthread_mutex_t *mutex)
{
  KEYCACHE_THREAD_TRACE_END("");
  pthread_mutex_unlock(mutex);
  return;
}


static int ___pagecache_pthread_cond_signal(pthread_cond_t *cond)
{
  int rc;
  KEYCACHE_THREAD_TRACE("signal");
  rc= pthread_cond_signal(cond);
  return rc;
}


#if defined(PAGECACHE_DEBUG_LOG)


static void pagecache_debug_print(const char * fmt, ...)
{
  va_list args;
  va_start(args,fmt);
  if (pagecache_debug_log)
  {
    VOID(vfprintf(pagecache_debug_log, fmt, args));
    VOID(fputc('\n',pagecache_debug_log));
  }
  va_end(args);
}
#endif /* defined(PAGECACHE_DEBUG_LOG) */

#if defined(PAGECACHE_DEBUG_LOG)


void pagecache_debug_log_close(void)
{
  if (pagecache_debug_log)
    fclose(pagecache_debug_log);
}
#endif /* defined(PAGECACHE_DEBUG_LOG) */

#endif /* defined(PAGECACHE_DEBUG) */