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1 /*
2  * Copyright (c) 2008-2012 Niels Provos and Nick Mathewson
3  *
4  * Redistribution and use in source and binary forms, with or without
5  * modification, are permitted provided that the following conditions
6  * are met:
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.
14  *
15  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
25  */
26 #ifndef EVENT2_THREAD_H_INCLUDED_
27 #define EVENT2_THREAD_H_INCLUDED_
28 
29 /** @file event2/thread.h
30 
31   Functions for multi-threaded applications using Libevent.
32 
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.
36 
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
39   use them.
40 
41   Most programs will either be using Windows threads or Posix threads.  You
42   can configure Libevent to use one of these event_use_windows_threads() or
43   event_use_pthreads() respectively.  If you're using another threading
44   library, you'll need to configure threading functions manually using
45   evthread_set_lock_callbacks() and evthread_set_condition_callbacks().
46 
47  */
48 
49 #include <event2/visibility.h>
50 
51 #ifdef __cplusplus
52 extern "C" {
53 #endif
54 
55 #include <event2/event-config.h>
56 
57 /**
58    @name Flags passed to lock functions
59 
60    @{
61 */
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
72 /**@}*/
73 
74 #if !defined(EVENT__DISABLE_THREAD_SUPPORT) || defined(EVENT_IN_DOXYGEN_)
75 
76 #define EVTHREAD_LOCK_API_VERSION 1
77 
78 /**
79    @name Types of locks
80 
81    @{*/
82 /** A recursive lock is one that can be acquired multiple times at once by the
83  * same thread.  No other process can allocate the lock until the thread that
84  * has been holding it has unlocked it as many times as it locked it. */
85 #define EVTHREAD_LOCKTYPE_RECURSIVE 1
86 /* A read-write lock is one that allows multiple simultaneous readers, but
87  * where any one writer excludes all other writers and readers. */
88 #define EVTHREAD_LOCKTYPE_READWRITE 2
89 /**@}*/
90 
91 /** This structure describes the interface a threading library uses for
92  * locking.   It's used to tell evthread_set_lock_callbacks() how to use
93  * locking on this platform.
94  */
95 struct evthread_lock_callbacks {
96 	/** The current version of the locking API.  Set this to
97 	 * EVTHREAD_LOCK_API_VERSION */
98 	int lock_api_version;
99 	/** Which kinds of locks does this version of the locking API
100 	 * support?  A bitfield of EVTHREAD_LOCKTYPE_RECURSIVE and
101 	 * EVTHREAD_LOCKTYPE_READWRITE.
102 	 *
103 	 * (Note that RECURSIVE locks are currently mandatory, and
104 	 * READWRITE locks are not currently used.)
105 	 **/
106 	unsigned supported_locktypes;
107 	/** Function to allocate and initialize new lock of type 'locktype'.
108 	 * Returns NULL on failure. */
109 	void *(*alloc)(unsigned locktype);
110 	/** Funtion to release all storage held in 'lock', which was created
111 	 * with type 'locktype'. */
112 	void (*free)(void *lock, unsigned locktype);
113 	/** Acquire an already-allocated lock at 'lock' with mode 'mode'.
114 	 * Returns 0 on success, and nonzero on failure. */
115 	int (*lock)(unsigned mode, void *lock);
116 	/** Release a lock at 'lock' using mode 'mode'.  Returns 0 on success,
117 	 * and nonzero on failure. */
118 	int (*unlock)(unsigned mode, void *lock);
119 };
120 
121 /** Sets a group of functions that Libevent should use for locking.
122  * For full information on the required callback API, see the
123  * documentation for the individual members of evthread_lock_callbacks.
124  *
125  * Note that if you're using Windows or the Pthreads threading library, you
126  * probably shouldn't call this function; instead, use
127  * evthread_use_windows_threads() or evthread_use_posix_threads() if you can.
128  */
129 EVENT2_EXPORT_SYMBOL
130 int evthread_set_lock_callbacks(const struct evthread_lock_callbacks *);
131 
132 #define EVTHREAD_CONDITION_API_VERSION 1
133 
134 struct timeval;
135 
136 /** This structure describes the interface a threading library uses for
137  * condition variables.  It's used to tell evthread_set_condition_callbacks
138  * how to use locking on this platform.
139  */
140 struct evthread_condition_callbacks {
141 	/** The current version of the conditions API.  Set this to
142 	 * EVTHREAD_CONDITION_API_VERSION */
143 	int condition_api_version;
144 	/** Function to allocate and initialize a new condition variable.
145 	 * Returns the condition variable on success, and NULL on failure.
146 	 * The 'condtype' argument will be 0 with this API version.
147 	 */
148 	void *(*alloc_condition)(unsigned condtype);
149 	/** Function to free a condition variable. */
150 	void (*free_condition)(void *cond);
151 	/** Function to signal a condition variable.  If 'broadcast' is 1, all
152 	 * threads waiting on 'cond' should be woken; otherwise, only on one
153 	 * thread is worken.  Should return 0 on success, -1 on failure.
154 	 * This function will only be called while holding the associated
155 	 * lock for the condition.
156 	 */
157 	int (*signal_condition)(void *cond, int broadcast);
158 	/** Function to wait for a condition variable.  The lock 'lock'
159 	 * will be held when this function is called; should be released
160 	 * while waiting for the condition to be come signalled, and
161 	 * should be held again when this function returns.
162 	 * If timeout is provided, it is interval of seconds to wait for
163 	 * the event to become signalled; if it is NULL, the function
164 	 * should wait indefinitely.
165 	 *
166 	 * The function should return -1 on error; 0 if the condition
167 	 * was signalled, or 1 on a timeout. */
168 	int (*wait_condition)(void *cond, void *lock,
169 	    const struct timeval *timeout);
170 };
171 
172 /** Sets a group of functions that Libevent should use for condition variables.
173  * For full information on the required callback API, see the
174  * documentation for the individual members of evthread_condition_callbacks.
175  *
176  * Note that if you're using Windows or the Pthreads threading library, you
177  * probably shouldn't call this function; instead, use
178  * evthread_use_windows_threads() or evthread_use_pthreads() if you can.
179  */
180 EVENT2_EXPORT_SYMBOL
181 int evthread_set_condition_callbacks(
182 	const struct evthread_condition_callbacks *);
183 
184 /**
185    Sets the function for determining the thread id.
186 
187    @param base the event base for which to set the id function
188    @param id_fn the identify function Libevent should invoke to
189      determine the identity of a thread.
190 */
191 EVENT2_EXPORT_SYMBOL
192 void evthread_set_id_callback(
193     unsigned long (*id_fn)(void));
194 
195 #if (defined(_WIN32) && !defined(EVENT__DISABLE_THREAD_SUPPORT)) || defined(EVENT_IN_DOXYGEN_)
196 /** Sets up Libevent for use with Windows builtin locking and thread ID
197     functions.  Unavailable if Libevent is not built for Windows.
198 
199     @return 0 on success, -1 on failure. */
200 EVENT2_EXPORT_SYMBOL
201 int evthread_use_windows_threads(void);
202 /**
203    Defined if Libevent was built with support for evthread_use_windows_threads()
204 */
205 #define EVTHREAD_USE_WINDOWS_THREADS_IMPLEMENTED 1
206 #endif
207 
208 #if defined(EVENT__HAVE_PTHREADS) || defined(EVENT_IN_DOXYGEN_)
209 /** Sets up Libevent for use with Pthreads locking and thread ID functions.
210     Unavailable if Libevent is not build for use with pthreads.  Requires
211     libraries to link against Libevent_pthreads as well as Libevent.
212 
213     @return 0 on success, -1 on failure. */
214 EVENT2_EXPORT_SYMBOL
215 int evthread_use_pthreads(void);
216 /** Defined if Libevent was built with support for evthread_use_pthreads() */
217 #define EVTHREAD_USE_PTHREADS_IMPLEMENTED 1
218 
219 #endif
220 
221 /** Enable debugging wrappers around the current lock callbacks.  If Libevent
222  * makes one of several common locking errors, exit with an assertion failure.
223  *
224  * If you're going to call this function, you must do so before any locks are
225  * allocated.
226  **/
227 EVENT2_EXPORT_SYMBOL
228 void evthread_enable_lock_debugging(void);
229 
230 /* Old (misspelled) version: This is deprecated; use
231  * evthread_enable_log_debugging instead. */
232 EVENT2_EXPORT_SYMBOL
233 void evthread_enable_lock_debuging(void);
234 
235 #endif /* EVENT__DISABLE_THREAD_SUPPORT */
236 
237 struct event_base;
238 /** Make sure it's safe to tell an event base to wake up from another thread
239     or a signal handler.
240 
241     You shouldn't need to call this by hand; configuring the base with thread
242     support should be necessary and sufficient.
243 
244     @return 0 on success, -1 on failure.
245  */
246 EVENT2_EXPORT_SYMBOL
247 int evthread_make_base_notifiable(struct event_base *base);
248 
249 #ifdef __cplusplus
250 }
251 #endif
252 
253 #endif /* EVENT2_THREAD_H_INCLUDED_ */
254