A follow-up to the patch for bug #56405 "Deadlock in the MDL deadlock

detector". This patch addresses performance regression in OLTP_RO/MyISAM
test on Windows introduced by the fix for bug #56405. Thus it makes
original patch acceptable as a solution for bug #56585 "Slowdown of
readonly sysbench benchmarks (e.g point_select) on Windows 5.5".

With this patch, MySQL will use native Windows condition variables and 
reader-writer locks  if  they are supported by the OS.

This speeds up MyISAM and the effect comes mostly from using native
rwlocks. Native conditions improve scalability with higher number of 
concurrent users in other situations, e.g for prlocks.

Benchmark numbers for this patch as measured on Win2008R2 quad
core machine are attached to the bug report.
( direct link http://bugs.mysql.com/file.php?id=15883 )

Note that currently we require at least Windows7/WS2008R2 for 
reader-writer locks, even though native rwlock is available also on Vista.
Reason is that "trylock" APIs are missing on Vista, and trylock is used in
the server (in a single place in query cache).

While this patch could have been written differently, to enable the native
rwlock optimization also on Vista/WS2008 (e.g using native locks everywhere
but portable implementation in query cache), this would come at the 
expense of the code clarity, as it would introduce a new  "try-able" rwlock
type, to handle Vista case.

Another way to improve performance for the special case 
(OLTP_RO/MYISAM/Vista) would be to eliminate "trylock" usage from server,
 but this is outside of the scope here.


Native conditions variables are used beginning with Vista though the effect
of using condition variables alone is not measurable in this benchmark.
But when used together with native rwlocks on Win7, native conditions improve 
performance in high-concurrency OLTP_RO/MyISAM (128 and more sysbench 
users).

1 files changed, 67 insertions, 13 deletions

diff --git a/include/my_pthread.h b/include/my_pthread.h
index 27ab5ba23fe..d3053b4861a 100644
--- a/include/my_pthread.h
+++ b/include/my_pthread.h
@@ -48,19 +48,30 @@ typedef struct st_pthread_link {
   struct st_pthread_link *next;
 } pthread_link;
 
-typedef struct {
-  uint32 waiting;
-  CRITICAL_SECTION lock_waiting;
- 
-  enum {
-    SIGNAL= 0,
-    BROADCAST= 1,
-    MAX_EVENTS= 2
-  } EVENTS;
-
-  HANDLE events[MAX_EVENTS];
-  HANDLE broadcast_block_event;
-
+/**
+  Implementation of Windows condition variables.
+  We use native conditions on Vista and later, and fallback to own 
+  implementation on earlier OS version.
+*/
+typedef union
+{
+  /* Native condition (used on Vista and later) */
+  CONDITION_VARIABLE native_cond;
+
+  /* Own implementation (used on XP) */
+  struct
+  { 
+    uint32 waiting;
+    CRITICAL_SECTION lock_waiting;
+    enum 
+    {
+      SIGNAL= 0,
+      BROADCAST= 1,
+      MAX_EVENTS= 2
+    } EVENTS;
+    HANDLE events[MAX_EVENTS];
+    HANDLE broadcast_block_event;
+  };
 } pthread_cond_t;
 
 
@@ -679,6 +690,47 @@ extern int rw_pr_destroy(rw_pr_lock_t *);
 
 
 #ifdef NEED_MY_RW_LOCK
+
+#ifdef _WIN32
+
+/**
+  Implementation of Windows rwlock.
+
+  We use native (slim) rwlocks on Win7 and later, and fallback to  portable
+  implementation on earlier Windows.
+
+  slim rwlock are also available on Vista/WS2008, but we do not use it
+  ("trylock" APIs are missing on Vista)
+*/
+typedef union
+{
+  /* Native rwlock (is_srwlock == TRUE) */
+  struct 
+  {
+    SRWLOCK srwlock;             /* native reader writer lock */
+    BOOL have_exclusive_srwlock; /* used for unlock */
+  };
+
+  /*
+    Portable implementation (is_srwlock == FALSE)
+    Fields are identical with Unix my_rw_lock_t fields.
+  */
+  struct 
+  {
+    pthread_mutex_t lock;       /* lock for structure		*/
+    pthread_cond_t  readers;    /* waiting readers		*/
+    pthread_cond_t  writers;    /* waiting writers		*/
+    int state;                  /* -1:writer,0:free,>0:readers	*/
+    int waiters;                /* number of waiting writers	*/
+#ifdef SAFE_MUTEX
+    pthread_t  write_thread;
+#endif
+  };
+} my_rw_lock_t;
+
+
+#else /* _WIN32 */
+
 /*
   On systems which don't support native read/write locks we have
   to use own implementation.
@@ -694,6 +746,8 @@ typedef struct st_my_rw_lock_t {
 #endif
 } my_rw_lock_t;
 
+#endif /*! _WIN32 */
+
 extern int my_rw_init(my_rw_lock_t *);
 extern int my_rw_destroy(my_rw_lock_t *);
 extern int my_rw_rdlock(my_rw_lock_t *);