/* Copyright (C) 2003-2007 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., 51 Franklin Street, Fifth Floor, Boston, MA 02111-1301 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 "my_safehash.h" /***************************************************************************** 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). *****************************************************************************/ /* Free a SAFE_HASH_ENTRY SYNOPSIS safe_hash_entry_free() entry The entry which should be freed NOTE This function is called by the hash object on delete */ static void safe_hash_entry_free(SAFE_HASH_ENTRY *entry) { DBUG_ENTER("safe_hash_entry_free"); my_free(entry); DBUG_VOID_RETURN; } /* Get key and length for a SAFE_HASH_ENTRY SYNOPSIS safe_hash_entry_get() entry The entry for which the key should be returned length Length of the key RETURN # reference on the key */ 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 */ my_bool safe_hash_init(SAFE_HASH *hash, uint elements, uchar *default_value) { DBUG_ENTER("safe_hash_init"); 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); } mysql_rwlock_init(key_SAFEHASH_mutex, &hash->mutex); hash->default_value= default_value; hash->root= 0; DBUG_RETURN(0); } /* Free a SAFE_HASH object SYNOPSIS safe_hash_free() hash Hash handle NOTES This is safe to call on any object that has been sent to safe_hash_init() */ 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); mysql_rwlock_destroy(&hash->mutex); hash->default_value=0; } } /* Return the value stored for a key or default value if no key SYNOPSIS safe_hash_search() hash Hash handle key key (path to table etc..) length Length of key def Default value of data RETURN # data associated with the key of default value if data was not found */ uchar *safe_hash_search(SAFE_HASH *hash, const uchar *key, uint length, uchar *def) { uchar *result; DBUG_ENTER("safe_hash_search"); mysql_rwlock_rdlock(&hash->mutex); result= my_hash_search(&hash->hash, key, length); mysql_rwlock_unlock(&hash->mutex); if (!result) result= def; else result= ((SAFE_HASH_ENTRY*) result)->data; DBUG_PRINT("exit",("data: %p", result)); DBUG_RETURN(result); } /* Associate a key with some data SYNOPSIS 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. */ 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: %p", length, key, data)); mysql_rwlock_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: mysql_rwlock_unlock(&hash->mutex); DBUG_RETURN(error); } /* Change all entries with one data value to another data value SYNOPSIS 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. */ void safe_hash_change(SAFE_HASH *hash, uchar *old_data, uchar *new_data) { SAFE_HASH_ENTRY *entry, *next; DBUG_ENTER("safe_hash_change"); mysql_rwlock_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; } } mysql_rwlock_unlock(&hash->mutex); DBUG_VOID_RETURN; }