2 * Copyright (c) 2008-2010 Niels Provos and Nick Mathewson
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
7 * 1. Redistributions of source code must retain the above copyright
8 * notice, this list of conditions and the following disclaimer.
9 * 2. Redistributions in binary form must reproduce the above copyright
10 * notice, this list of conditions and the following disclaimer in the
11 * documentation and/or other materials provided with the distribution.
12 * 3. The name of the author may not be used to endorse or promote products
13 * derived from this software without specific prior written permission.
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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26 #ifndef _EVENT2_THREAD_H_
27 #define _EVENT2_THREAD_H_
31 Functions for multi-threaded applications using Libevent.
33 When using a multi-threaded application in which multiple threads
34 add and delete events from a single event base, Libevent needs to
35 lock its data structures.
37 Like the memory-management function hooks, all of the threading functions
38 _must_ be set up before an event_base is created if you want the base to
41 A multi-threaded application must provide locking functions to
42 Libevent via evthread_set_locking_callback(). Libevent will invoke
43 this callback whenever a lock needs to be acquired or released.
45 The total number of locks employed by Libevent can be determined
46 via the evthread_num_locks() function. An application must provision
49 If the owner of an event base is waiting for events to happen,
50 Libevent may signal the thread via a special file descriptor to wake
51 up. To enable this feature, an application needs to provide a
52 thread identity function via evthread_set_id_callback().
60 #include <event2/event-config.h>
62 /** A flag passed to a locking callback when the lock was allocated as a
63 * read-write lock, and we want to acquire or release the lock for writing. */
64 #define EVTHREAD_WRITE 0x04
65 /** A flag passed to a locking callback when the lock was allocated as a
66 * read-write lock, and we want to acquire or release the lock for reading. */
67 #define EVTHREAD_READ 0x08
68 /** A flag passed to a locking callback when we don't want to block waiting
69 * for the lock; if we can't get the lock immediately, we will instead
70 * return nonzero from the locking callback. */
71 #define EVTHREAD_TRY 0x10
73 #ifndef _EVENT_DISABLE_THREAD_SUPPORT
75 #define EVTHREAD_LOCK_API_VERSION 1
77 /** A recursive lock is one that can be acquired multiple times at once by the
78 * same thread. No other process can allocate the lock until the thread that
79 * has been holding it has unlocked it as many times as it locked it. */
80 #define EVTHREAD_LOCKTYPE_RECURSIVE 1
81 /* A read-write lock is one that allows multiple simultaneous readers, but
82 * where any one writer excludes all other writers and readers. */
83 #define EVTHREAD_LOCKTYPE_READWRITE 2
85 /** This structure describes the interface a threading library uses for
86 * locking. It's used to tell evthread_set_lock_callbacks how to use
87 * locking on this platform.
89 struct evthread_lock_callbacks {
90 /** The current version of the locking API. Set this to
91 * EVTHREAD_LOCK_API_VERSION */
93 /** Which kinds of locks does this version of the locking API
94 * support? A bitfield of EVTHREAD_LOCKTYPE_RECURSIVE and
95 * EVTHREAD_LOCKTYPE_READWRITE.
97 * (Note that RECURSIVE locks are currently mandatory, and
98 * READWRITE locks are not currently used.)
100 unsigned supported_locktypes;
101 /** Function to allocate and initialize new lock of type 'locktype'.
102 * Returns NULL on failure. */
103 void *(*alloc)(unsigned locktype);
104 /** Funtion to release all storage held in 'lock', which was created
105 * with type 'locktype'. */
106 void (*free)(void *lock, unsigned locktype);
107 /** Acquire an already-allocated lock at 'lock' with mode 'mode'.
108 * Returns 0 on success, and nonzero on failure. */
109 int (*lock)(unsigned mode, void *lock);
110 /** Release a lock at 'lock' using mode 'mode'. Returns 0 on success,
111 * and nonzero on failure. */
112 int (*unlock)(unsigned mode, void *lock);
115 /** Sets a group of functions that Libevent should use for locking.
116 * For full information on the required callback API, see the
117 * documentation for the individual members of evthread_lock_callbacks.
119 * Note that if you're using Windows or the Pthreads threading library, you
120 * probably shouldn't call this function; instead, use
121 * evthread_use_windows_threads() or evthread_use_posix_threads() if you can.
123 int evthread_set_lock_callbacks(const struct evthread_lock_callbacks *);
125 #define EVTHREAD_CONDITION_API_VERSION 1
129 /** This structure describes the interface a threading library uses for
130 * condition variables. It's used to tell evthread_set_condition_callbacks
131 * how to use locking on this platform.
133 struct evthread_condition_callbacks {
134 /** The current version of the conditions API. Set this to
135 * EVTHREAD_CONDITION_API_VERSION */
136 int condition_api_version;
137 /** Function to allocate and initialize a new condition variable.
138 * Returns the condition variable on success, and NULL on failure.
139 * The 'condtype' argument will be 0 with this API version.
141 void *(*alloc_condition)(unsigned condtype);
142 /** Function to free a condition variable. */
143 void (*free_condition)(void *cond);
144 /** Function to signal a condition variable. If 'broadcast' is 1, all
145 * threads waiting on 'cond' should be woken; otherwise, only on one
146 * thread is worken. Should return 0 on success, -1 on failure.
147 * This function will only be called while holding the associated
148 * lock for the condition.
150 int (*signal_condition)(void *cond, int broadcast);
151 /** Function to wait for a condition variable. The lock 'lock'
152 * will be held when this function is called; should be released
153 * while waiting for the condition to be come signalled, and
154 * should be held again when this function returns.
155 * If timeout is provided, it is interval of seconds to wait for
156 * the event to become signalled; if it is NULL, the function
157 * should wait indefinitely.
159 * The function should return -1 on error; 0 if the condition
160 * was signalled, or 1 on a timeout. */
161 int (*wait_condition)(void *cond, void *lock,
162 const struct timeval *timeout);
165 /** Sets a group of functions that Libevent should use for condition variables.
166 * For full information on the required callback API, see the
167 * documentation for the individual members of evthread_condition_callbacks.
169 * Note that if you're using Windows or the Pthreads threading library, you
170 * probably shouldn't call this function; instead, use
171 * evthread_use_windows_threads() or evthread_use_posix_threads() if you can.
173 int evthread_set_condition_callbacks(
174 const struct evthread_condition_callbacks *);
177 Sets the function for determining the thread id.
179 @param base the event base for which to set the id function
180 @param id_fn the identify function Libevent should invoke to
181 determine the identity of a thread.
183 void evthread_set_id_callback(
184 unsigned long (*id_fn)(void));
186 #if defined(WIN32) && !defined(_EVENT_DISABLE_THREAD_SUPPORT)
187 /** Sets up Libevent for use with Windows builtin locking and thread ID
188 functions. Unavailable if Libevent is not built for Windows.
190 @return 0 on success, -1 on failure. */
191 int evthread_use_windows_threads(void);
192 #define EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED 1
195 #if defined(_EVENT_HAVE_PTHREADS)
196 /** Sets up Libevent for use with Pthreads locking and thread ID functions.
197 Unavailable if Libevent is not build for use with pthreads. Requires
198 libraries to link against Libevent_pthreads as well as Libevent.
200 @return 0 on success, -1 on failure. */
201 int evthread_use_pthreads(void);
202 #define EVTHREAD_USE_PTHREADS_IMPLEMENTED 1
206 /** Enable debugging wrappers around the current lock callbacks. If Libevent
207 * makes one of several common locking errors, exit with an assertion failure.
209 void evthread_enable_lock_debuging(void);
211 #endif /* _EVENT_DISABLE_THREAD_SUPPORT */
214 /** Make sure it's safe to tell an event base to wake up from another thread.
217 @return 0 on success, -1 on failure.
219 int evthread_make_base_notifiable(struct event_base *base);
225 #endif /* _EVENT2_THREAD_H_ */