Current File : //usr/include/mysql/server/mysql/service_thd_specifics.h
#ifndef MYSQL_SERVICE_THD_SPECIFICS_INCLUDED
/* Copyright (c) 2009, 2010, Oracle and/or its affiliates. All rights reserved.
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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1335 USA */
/**
@file
THD specific for plugin(s)
This API provides pthread_getspecific like functionality to plugin authors.
This is a functional alternative to the declarative MYSQL_THDVAR
A plugin should at init call thd_key_create that create a key that
will have storage in each THD. The key should be used by all threads
and can be used concurrently from all threads.
A plugin should at deinit call thd_key_delete.
Alternatively, a plugin can use thd_key_create_from_var(K,V) to create
a key that corresponds to a named MYSQL_THDVAR variable.
This API is also safe when using pool-of-threads in which case
pthread_getspecific is not, because the actual OS thread may change.
@note
Normally one should prefer MYSQL_THDVAR declarative API.
The benefits are:
- It supports typed variables (int, char*, enum, etc), not only void*.
- The memory allocated for MYSQL_THDVAR is free'd automatically
(if PLUGIN_VAR_MEMALLOC is specified).
- Continuous loading and unloading of the same plugin does not allocate
memory for same variables over and over again.
An example of using MYSQL_THDVAR for a thd local storage:
MYSQL_THDVAR_STR(my_tls,
PLUGIN_VAR_MEMALLOC | PLUGIN_VAR_NOSYSVAR | PLUGIN_VAR_NOCMDOPT,
"thd local storage example", 0, 0, 0);
*/
#ifdef __cplusplus
extern "C" {
#endif
typedef int MYSQL_THD_KEY_T;
extern struct thd_specifics_service_st {
int (*thd_key_create_func)(MYSQL_THD_KEY_T *key);
void (*thd_key_delete_func)(MYSQL_THD_KEY_T *key);
void *(*thd_getspecific_func)(MYSQL_THD thd, MYSQL_THD_KEY_T key);
int (*thd_setspecific_func)(MYSQL_THD thd, MYSQL_THD_KEY_T key, void *value);
} *thd_specifics_service;
#define thd_key_create_from_var(K, V) do { *(K)= MYSQL_SYSVAR_NAME(V).offset; } while(0)
#ifdef MYSQL_DYNAMIC_PLUGIN
#define thd_key_create(K) (thd_specifics_service->thd_key_create_func(K))
#define thd_key_delete(K) (thd_specifics_service->thd_key_delete_func(K))
#define thd_getspecific(T, K) (thd_specifics_service->thd_getspecific_func(T, K))
#define thd_setspecific(T, K, V) (thd_specifics_service->thd_setspecific_func(T, K, V))
#else
/**
* create THD specific storage
* @return 0 on success
* else errno is returned
*/
int thd_key_create(MYSQL_THD_KEY_T *key);
/**
* delete THD specific storage
*/
void thd_key_delete(MYSQL_THD_KEY_T *key);
/**
* get/set thd specific storage
* - first time this is called from a thread it will return 0
* - this call is thread-safe in that different threads may call this
* simultaneously if operating on different THDs.
* - this call acquires no mutexes and is implemented as an array lookup
*/
void* thd_getspecific(MYSQL_THD thd, MYSQL_THD_KEY_T key);
int thd_setspecific(MYSQL_THD thd, MYSQL_THD_KEY_T key, void *value);
#endif
#ifdef __cplusplus
}
#endif
#define MYSQL_SERVICE_THD_SPECIFICS_INCLUDED
#endif
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