/* Copyright (C) 2003 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; version 2 of the License. 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 */ /* Handling of multiple key caches The idea is to have a thread safe hash on the table name, with a default key cache value that is returned if the table name is not in the cache. */ #include "mysys_priv.h" #include #include #include /***************************************************************************** General functions to handle SAFE_HASH objects. A SAFE_HASH object is used to store the hash, the mutex and default value needed by the rest of the key cache code. This is a separate struct to make it easy to later reuse the code for other purposes All entries are linked in a list to allow us to traverse all elements and delete selected ones. (HASH doesn't allow any easy ways to do this). *****************************************************************************/ /* Struct to store a key and pointer to object */ typedef struct st_safe_hash_entry { uchar *key; uint length; uchar *data; struct st_safe_hash_entry *next, **prev; } SAFE_HASH_ENTRY; typedef struct st_safe_hash_with_default { #ifdef THREAD rw_lock_t mutex; #endif HASH hash; uchar *default_value; SAFE_HASH_ENTRY *root; } SAFE_HASH; /* Free a SAFE_HASH_ENTRY This function is called by the hash object on delete */ static void safe_hash_entry_free(SAFE_HASH_ENTRY *entry) { DBUG_ENTER("free_assign_entry"); my_free(entry); DBUG_VOID_RETURN; } /* Get key and length for a SAFE_HASH_ENTRY */ static uchar *safe_hash_entry_get(SAFE_HASH_ENTRY *entry, size_t *length, my_bool not_used __attribute__((unused))) { *length=entry->length; return (uchar*) entry->key; } /* Init a SAFE_HASH object SYNOPSIS safe_hash_init() hash safe_hash handler elements Expected max number of elements default_value default value NOTES In case of error we set hash->default_value to 0 to allow one to call safe_hash_free on an object that couldn't be initialized. RETURN 0 ok 1 error */ static my_bool safe_hash_init(SAFE_HASH *hash, uint elements, uchar *default_value) { DBUG_ENTER("safe_hash"); if (my_hash_init(&hash->hash, &my_charset_bin, elements, 0, 0, (my_hash_get_key) safe_hash_entry_get, (void (*)(void*)) safe_hash_entry_free, 0)) { hash->default_value= 0; DBUG_RETURN(1); } my_rwlock_init(&hash->mutex, 0); hash->default_value= default_value; hash->root= 0; DBUG_RETURN(0); } /* Free a SAFE_HASH object NOTES This is safe to call on any object that has been sent to safe_hash_init() */ static void safe_hash_free(SAFE_HASH *hash) { /* Test if safe_hash_init succeeded. This will also guard us against multiple free calls. */ if (hash->default_value) { my_hash_free(&hash->hash); rwlock_destroy(&hash->mutex); hash->default_value=0; } } /* Return the value stored for a key or default value if no key */ static uchar *safe_hash_search(SAFE_HASH *hash, const uchar *key, uint length) { uchar *result; DBUG_ENTER("safe_hash_search"); rw_rdlock(&hash->mutex); result= my_hash_search(&hash->hash, key, length); rw_unlock(&hash->mutex); if (!result) result= hash->default_value; else result= ((SAFE_HASH_ENTRY*) result)->data; DBUG_PRINT("exit",("data: 0x%lx", (long) result)); DBUG_RETURN(result); } /* Associate a key with some data SYONOPSIS safe_hash_set() hash Hash handle key key (path to table etc..) length Length of key data data to to associate with the data NOTES This can be used both to insert a new entry and change an existing entry. If one associates a key with the default key cache, the key is deleted RETURN 0 ok 1 error (Can only be EOM). In this case my_message() is called. */ static my_bool safe_hash_set(SAFE_HASH *hash, const uchar *key, uint length, uchar *data) { SAFE_HASH_ENTRY *entry; my_bool error= 0; DBUG_ENTER("safe_hash_set"); DBUG_PRINT("enter",("key: %.*s data: 0x%lx", length, key, (long) data)); rw_wrlock(&hash->mutex); entry= (SAFE_HASH_ENTRY*) my_hash_search(&hash->hash, key, length); if (data == hash->default_value) { /* The key is to be associated with the default entry. In this case we can just delete the entry (if it existed) from the hash as a search will return the default entry */ if (!entry) /* nothing to do */ goto end; /* unlink entry from list */ if ((*entry->prev= entry->next)) entry->next->prev= entry->prev; my_hash_delete(&hash->hash, (uchar*) entry); goto end; } if (entry) { /* Entry existed; Just change the pointer to point at the new data */ entry->data= data; } else { if (!(entry= (SAFE_HASH_ENTRY *) my_malloc(sizeof(*entry) + length, MYF(MY_WME)))) { error= 1; goto end; } entry->key= (uchar*) (entry +1); memcpy((char*) entry->key, (char*) key, length); entry->length= length; entry->data= data; /* Link entry to list */ if ((entry->next= hash->root)) entry->next->prev= &entry->next; entry->prev= &hash->root; hash->root= entry; if (my_hash_insert(&hash->hash, (uchar*) entry)) { /* This can only happen if hash got out of memory */ my_free(entry); error= 1; goto end; } } end: rw_unlock(&hash->mutex); DBUG_RETURN(error); } /* Change all entres with one data value to another data value SYONOPSIS safe_hash_change() hash Hash handle old_data Old data new_data Change all 'old_data' to this NOTES We use the linked list to traverse all elements in the hash as this allows us to delete elements in the case where 'new_data' is the default value. */ static void safe_hash_change(SAFE_HASH *hash, uchar *old_data, uchar *new_data) { SAFE_HASH_ENTRY *entry, *next; DBUG_ENTER("safe_hash_set"); rw_wrlock(&hash->mutex); for (entry= hash->root ; entry ; entry= next) { next= entry->next; if (entry->data == old_data) { if (new_data == hash->default_value) { if ((*entry->prev= entry->next)) entry->next->prev= entry->prev; my_hash_delete(&hash->hash, (uchar*) entry); } else entry->data= new_data; } } rw_unlock(&hash->mutex); DBUG_VOID_RETURN; } /***************************************************************************** Functions to handle the key cache objects *****************************************************************************/ /* Variable to store all key cache objects */ static SAFE_HASH key_cache_hash; my_bool multi_keycache_init(void) { return safe_hash_init(&key_cache_hash, 16, (uchar*) dflt_key_cache); } void multi_keycache_free(void) { safe_hash_free(&key_cache_hash); } /* Get a key cache to be used for a specific table. SYNOPSIS multi_key_cache_search() key key to find (usually table path) uint length Length of key. NOTES This function is coded in such a way that we will return the default key cache even if one never called multi_keycache_init. This will ensure that it works with old MyISAM clients. RETURN key cache to use */ KEY_CACHE *multi_key_cache_search(uchar *key, uint length) { if (!key_cache_hash.hash.records) return dflt_key_cache; return (KEY_CACHE*) safe_hash_search(&key_cache_hash, key, length); } /* Assosiate a key cache with a key SYONOPSIS multi_key_cache_set() key key (path to table etc..) length Length of key key_cache cache to assococite with the table NOTES This can be used both to insert a new entry and change an existing entry */ my_bool multi_key_cache_set(const uchar *key, uint length, KEY_CACHE *key_cache) { return safe_hash_set(&key_cache_hash, key, length, (uchar*) key_cache); } void multi_key_cache_change(KEY_CACHE *old_data, KEY_CACHE *new_data) { safe_hash_change(&key_cache_hash, (uchar*) old_data, (uchar*) new_data); }