Wed Oct 28 11:45:43 2009

Asterisk developer's documentation


threadstorage.h

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00001 /*
00002  * Asterisk -- An open source telephony toolkit.
00003  *
00004  * Copyright (C) 2006, Digium, Inc.
00005  *
00006  * Russell Bryant <russell@digium.com>
00007  *
00008  * See http://www.asterisk.org for more information about
00009  * the Asterisk project. Please do not directly contact
00010  * any of the maintainers of this project for assistance;
00011  * the project provides a web site, mailing lists and IRC
00012  * channels for your use.
00013  *
00014  * This program is free software, distributed under the terms of
00015  * the GNU General Public License Version 2. See the LICENSE file
00016  * at the top of the source tree.
00017  */
00018 
00019 /*!
00020  * \file threadstorage.h
00021  * \author Russell Bryant <russell@digium.com>
00022  * \brief Definitions to aid in the use of thread local storage
00023  *
00024  * \arg \ref AstThreadStorage
00025  */
00026 
00027 /*!
00028  * \page AstThreadStorage The Asterisk Thread Storage API
00029  *
00030  *
00031  * The POSIX threads (pthreads) API provides the ability to define thread
00032  * specific data.  The functions and structures defined here are intended
00033  * to centralize the code that is commonly used when using thread local
00034  * storage.
00035  *
00036  * The motivation for using this code in Asterisk is for situations where
00037  * storing data on a thread-specific basis can provide some amount of
00038  * performance benefit.  For example, there are some call types in Asterisk
00039  * where ast_frame structures must be allocated very rapidly (easily 50, 100,
00040  * 200 times a second).  Instead of doing the equivalent of that many calls
00041  * to malloc() and free() per second, thread local storage is used to keep a
00042  * list of unused frame structures so that they can be continuously reused.
00043  *
00044  * - \ref threadstorage.h
00045  */
00046 
00047 #ifndef ASTERISK_THREADSTORAGE_H
00048 #define ASTERISK_THREADSTORAGE_H
00049 
00050 #include "asterisk/utils.h"
00051 #include "asterisk/inline_api.h"
00052 
00053 /*!
00054  * \brief data for a thread locally stored variable
00055  */
00056 struct ast_threadstorage {
00057    pthread_once_t once; /*!< Ensure that the key is only initialized by one thread */
00058    pthread_key_t key;   /*!< The key used to retrieve this thread's data */
00059    void (*key_init)(void); /*!< The function that initializes the key */
00060    int (*custom_init)(void *); /*!< Custom initialization function specific to the object */
00061 };
00062 
00063 #if defined(DEBUG_THREADLOCALS)
00064 void __ast_threadstorage_object_add(void *key, size_t len, const char *file, const char *function, unsigned int line);
00065 void __ast_threadstorage_object_remove(void *key);
00066 void __ast_threadstorage_object_replace(void *key_old, void *key_new, size_t len);
00067 #endif /* defined(DEBUG_THREADLOCALS) */
00068 
00069 /*!
00070  * \brief Define a thread storage variable
00071  *
00072  * \arg name The name of the thread storage object
00073  *
00074  * This macro would be used to declare an instance of thread storage in a file.
00075  *
00076  * Example usage:
00077  * \code
00078  * AST_THREADSTORAGE(my_buf);
00079  * \endcode
00080  */
00081 #define AST_THREADSTORAGE(name) \
00082    AST_THREADSTORAGE_CUSTOM(name, NULL, ast_free_ptr) 
00083 
00084 /*!
00085  * \brief Define a thread storage variable, with custom initialization and cleanup
00086  *
00087  * \arg name The name of the thread storage object
00088  * \arg init This is a custom function that will be called after each thread specific
00089  *           object is allocated, with the allocated block of memory passed
00090  *           as the argument.
00091  * \arg cleanup This is a custom function that will be called instead of ast_free
00092  *              when the thread goes away.  Note that if this is used, it *MUST*
00093  *              call free on the allocated memory.
00094  *
00095  * Example usage:
00096  * \code
00097  * AST_THREADSTORAGE_CUSTOM(my_buf, my_init, my_cleanup);
00098  * \endcode
00099  */
00100 #if !defined(DEBUG_THREADLOCALS)
00101 #define AST_THREADSTORAGE_CUSTOM(name, c_init, c_cleanup)   \
00102 static void __init_##name(void);                \
00103 static struct ast_threadstorage name = {        \
00104    .once = PTHREAD_ONCE_INIT,                  \
00105    .key_init = __init_##name,                  \
00106    .custom_init = c_init,                      \
00107 };                                              \
00108 static void __init_##name(void)                 \
00109 {                                               \
00110    pthread_key_create(&(name).key, c_cleanup); \
00111 }
00112 #else /* defined(DEBUG_THREADLOCALS) */
00113 #define AST_THREADSTORAGE_CUSTOM_SCOPE(name, c_init, c_cleanup, scope) \
00114 static void __init_##name(void);                \
00115 static struct ast_threadstorage name = {        \
00116    .once = PTHREAD_ONCE_INIT,                  \
00117    .key_init = __init_##name,                  \
00118    .custom_init = c_init,                      \
00119 };                                              \
00120 static void __cleanup_##name(void *data)        \
00121 {                                               \
00122    __ast_threadstorage_object_remove(data);    \
00123    c_cleanup(data);                            \
00124 }                                               \
00125 static void __init_##name(void)                 \
00126 {                                               \
00127    pthread_key_create(&(name).key, __cleanup_##name); \
00128 }
00129 #endif /* defined(DEBUG_THREADLOCALS) */
00130 
00131 /*!
00132  * \brief Retrieve thread storage
00133  *
00134  * \arg ts This is a pointer to the thread storage structure declared by using
00135  *      the AST_THREADSTORAGE macro.  If declared with 
00136  *      AST_THREADSTORAGE(my_buf), then this argument would be (&my_buf).
00137  * \arg init_size This is the amount of space to be allocated the first time
00138  *      this thread requests its data. Thus, this should be the size that the
00139  *      code accessing this thread storage is assuming the size to be.
00140  *
00141  * \return This function will return the thread local storage associated with
00142  *         the thread storage management variable passed as the first argument.
00143  *         The result will be NULL in the case of a memory allocation error.
00144  *
00145  * Example usage:
00146  * \code
00147  * AST_THREADSTORAGE(my_buf);
00148  * #define MY_BUF_SIZE   128
00149  * ...
00150  * void my_func(const char *fmt, ...)
00151  * {
00152  *      void *buf;
00153  *
00154  *      if (!(buf = ast_threadstorage_get(&my_buf, MY_BUF_SIZE)))
00155  *           return;
00156  *      ...
00157  * }
00158  * \endcode
00159  */
00160 #if !defined(DEBUG_THREADLOCALS)
00161 AST_INLINE_API(
00162 void *ast_threadstorage_get(struct ast_threadstorage *ts, size_t init_size),
00163 {
00164    void *buf;
00165 
00166    pthread_once(&ts->once, ts->key_init);
00167    if (!(buf = pthread_getspecific(ts->key))) {
00168       if (!(buf = ast_calloc(1, init_size)))
00169          return NULL;
00170       if (ts->custom_init && ts->custom_init(buf)) {
00171          free(buf);
00172          return NULL;
00173       }
00174       pthread_setspecific(ts->key, buf);
00175    }
00176 
00177    return buf;
00178 }
00179 )
00180 #else /* defined(DEBUG_THREADLOCALS) */
00181 AST_INLINE_API(
00182 void *__ast_threadstorage_get(struct ast_threadstorage *ts, size_t init_size, const char *file, const char *function, unsigned int line),
00183 {
00184    void *buf;
00185 
00186    pthread_once(&ts->once, ts->key_init);
00187    if (!(buf = pthread_getspecific(ts->key))) {
00188       if (!(buf = ast_calloc(1, init_size)))
00189          return NULL;
00190       if (ts->custom_init && ts->custom_init(buf)) {
00191          free(buf);
00192          return NULL;
00193       }
00194       pthread_setspecific(ts->key, buf);
00195       __ast_threadstorage_object_add(buf, init_size, file, function, line);
00196    }
00197 
00198    return buf;
00199 }
00200 )
00201 
00202 #define ast_threadstorage_get(ts, init_size) __ast_threadstorage_get(ts, init_size, __FILE__, __PRETTY_FUNCTION__, __LINE__)
00203 #endif /* defined(DEBUG_THREADLOCALS) */
00204 
00205 #endif /* ASTERISK_THREADSTORAGE_H */

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