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Diffstat (limited to '')
| -rw-r--r-- | mysys/my_safehash.c | 298 |
1 files changed, 298 insertions, 0 deletions
diff --git a/mysys/my_safehash.c b/mysys/my_safehash.c new file mode 100644 index 00000000..7d37b707 --- /dev/null +++ b/mysys/my_safehash.c @@ -0,0 +1,298 @@ +/* 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 02110-1335 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 <m_string.h> +#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(key_memory_SAFE_HASH_ENTRY, &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(key_memory_SAFE_HASH_ENTRY, + 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; +} |