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-rw-r--r--mysys/my_safehash.c298
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+/* 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;
+}
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