Mercurial > sdl-ios-xcode
annotate src/thread/generic/SDL_syscond.c @ 314:bff64eba7721
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| author | Sam Lantinga <slouken@libsdl.org> |
|---|---|
| date | Fri, 22 Mar 2002 18:11:56 +0000 |
| parents | f6ffac90895c |
| children | b8d311d90021 |
| rev | line source |
|---|---|
| 0 | 1 /* |
| 2 SDL - Simple DirectMedia Layer | |
|
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f6ffac90895c
Updated copyright information for 2002
Sam Lantinga <slouken@libsdl.org>
parents:
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3 Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002 Sam Lantinga |
| 0 | 4 |
| 5 This library is free software; you can redistribute it and/or | |
| 6 modify it under the terms of the GNU Library General Public | |
| 7 License as published by the Free Software Foundation; either | |
| 8 version 2 of the License, or (at your option) any later version. | |
| 9 | |
| 10 This library is distributed in the hope that it will be useful, | |
| 11 but WITHOUT ANY WARRANTY; without even the implied warranty of | |
| 12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
| 13 Library General Public License for more details. | |
| 14 | |
| 15 You should have received a copy of the GNU Library General Public | |
| 16 License along with this library; if not, write to the Free | |
| 17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
| 18 | |
| 19 Sam Lantinga | |
|
252
e8157fcb3114
Updated the source with the correct e-mail address
Sam Lantinga <slouken@libsdl.org>
parents:
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changeset
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20 slouken@libsdl.org |
| 0 | 21 */ |
| 22 | |
| 23 #ifdef SAVE_RCSID | |
| 24 static char rcsid = | |
| 25 "@(#) $Id$"; | |
| 26 #endif | |
| 27 | |
| 28 /* An implementation of condition variables using semaphores and mutexes */ | |
| 29 /* | |
| 30 This implementation borrows heavily from the BeOS condition variable | |
| 31 implementation, written by Christopher Tate and Owen Smith. Thanks! | |
| 32 */ | |
| 33 | |
| 34 #include <stdio.h> | |
| 35 #include <stdlib.h> | |
| 36 | |
| 37 #include "SDL_error.h" | |
| 38 #include "SDL_thread.h" | |
| 39 | |
| 40 struct SDL_cond | |
| 41 { | |
| 42 SDL_mutex *lock; | |
| 43 int waiting; | |
| 44 int signals; | |
| 45 SDL_sem *wait_sem; | |
| 46 SDL_sem *wait_done; | |
| 47 }; | |
| 48 | |
| 49 /* Create a condition variable */ | |
| 50 SDL_cond * SDL_CreateCond(void) | |
| 51 { | |
| 52 SDL_cond *cond; | |
| 53 | |
| 54 cond = (SDL_cond *) malloc(sizeof(SDL_cond)); | |
| 55 if ( cond ) { | |
| 56 cond->lock = SDL_CreateMutex(); | |
| 57 cond->wait_sem = SDL_CreateSemaphore(0); | |
| 58 cond->wait_done = SDL_CreateSemaphore(0); | |
| 59 cond->waiting = cond->signals = 0; | |
| 60 if ( ! cond->lock || ! cond->wait_sem || ! cond->wait_done ) { | |
| 61 SDL_DestroyCond(cond); | |
| 62 cond = NULL; | |
| 63 } | |
| 64 } else { | |
| 65 SDL_OutOfMemory(); | |
| 66 } | |
| 67 return(cond); | |
| 68 } | |
| 69 | |
| 70 /* Destroy a condition variable */ | |
| 71 void SDL_DestroyCond(SDL_cond *cond) | |
| 72 { | |
| 73 if ( cond ) { | |
| 74 if ( cond->wait_sem ) { | |
| 75 SDL_DestroySemaphore(cond->wait_sem); | |
| 76 } | |
| 77 if ( cond->wait_done ) { | |
| 78 SDL_DestroySemaphore(cond->wait_done); | |
| 79 } | |
| 80 if ( cond->lock ) { | |
| 81 SDL_DestroyMutex(cond->lock); | |
| 82 } | |
| 83 free(cond); | |
| 84 } | |
| 85 } | |
| 86 | |
| 87 /* Restart one of the threads that are waiting on the condition variable */ | |
| 88 int SDL_CondSignal(SDL_cond *cond) | |
| 89 { | |
| 90 if ( ! cond ) { | |
| 91 SDL_SetError("Passed a NULL condition variable"); | |
| 92 return -1; | |
| 93 } | |
| 94 | |
| 95 /* If there are waiting threads not already signalled, then | |
| 96 signal the condition and wait for the thread to respond. | |
| 97 */ | |
| 98 SDL_LockMutex(cond->lock); | |
| 99 if ( cond->waiting > cond->signals ) { | |
| 100 ++cond->signals; | |
| 101 SDL_SemPost(cond->wait_sem); | |
| 102 SDL_UnlockMutex(cond->lock); | |
| 103 SDL_SemWait(cond->wait_done); | |
| 104 } else { | |
| 105 SDL_UnlockMutex(cond->lock); | |
| 106 } | |
| 107 | |
| 108 return 0; | |
| 109 } | |
| 110 | |
| 111 /* Restart all threads that are waiting on the condition variable */ | |
| 112 int SDL_CondBroadcast(SDL_cond *cond) | |
| 113 { | |
| 114 if ( ! cond ) { | |
| 115 SDL_SetError("Passed a NULL condition variable"); | |
| 116 return -1; | |
| 117 } | |
| 118 | |
| 119 /* If there are waiting threads not already signalled, then | |
| 120 signal the condition and wait for the thread to respond. | |
| 121 */ | |
| 122 SDL_LockMutex(cond->lock); | |
| 123 if ( cond->waiting > cond->signals ) { | |
| 124 int i, num_waiting; | |
| 125 | |
| 126 num_waiting = (cond->waiting - cond->signals); | |
| 127 cond->signals = cond->waiting; | |
| 128 for ( i=0; i<num_waiting; ++i ) { | |
| 129 SDL_SemPost(cond->wait_sem); | |
| 130 } | |
| 131 /* Now all released threads are blocked here, waiting for us. | |
| 132 Collect them all (and win fabulous prizes!) :-) | |
| 133 */ | |
| 134 SDL_UnlockMutex(cond->lock); | |
| 135 for ( i=0; i<num_waiting; ++i ) { | |
| 136 SDL_SemWait(cond->wait_done); | |
| 137 } | |
| 138 } else { | |
| 139 SDL_UnlockMutex(cond->lock); | |
| 140 } | |
| 141 | |
| 142 return 0; | |
| 143 } | |
| 144 | |
| 145 /* Wait on the condition variable for at most 'ms' milliseconds. | |
| 146 The mutex must be locked before entering this function! | |
| 147 The mutex is unlocked during the wait, and locked again after the wait. | |
| 148 | |
| 149 Typical use: | |
| 150 | |
| 151 Thread A: | |
| 152 SDL_LockMutex(lock); | |
| 153 while ( ! condition ) { | |
| 154 SDL_CondWait(cond); | |
| 155 } | |
| 156 SDL_UnlockMutex(lock); | |
| 157 | |
| 158 Thread B: | |
| 159 SDL_LockMutex(lock); | |
| 160 ... | |
| 161 condition = true; | |
| 162 ... | |
| 163 SDL_UnlockMutex(lock); | |
| 164 */ | |
| 165 int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms) | |
| 166 { | |
| 167 int retval; | |
| 168 | |
| 169 if ( ! cond ) { | |
| 170 SDL_SetError("Passed a NULL condition variable"); | |
| 171 return -1; | |
| 172 } | |
| 173 | |
| 174 /* Obtain the protection mutex, and increment the number of waiters. | |
| 175 This allows the signal mechanism to only perform a signal if there | |
| 176 are waiting threads. | |
| 177 */ | |
| 178 SDL_LockMutex(cond->lock); | |
| 179 ++cond->waiting; | |
| 180 SDL_UnlockMutex(cond->lock); | |
| 181 | |
| 182 /* Unlock the mutex, as is required by condition variable semantics */ | |
| 183 SDL_UnlockMutex(mutex); | |
| 184 | |
| 185 /* Wait for a signal */ | |
| 186 if ( ms == SDL_MUTEX_MAXWAIT ) { | |
| 187 retval = SDL_SemWait(cond->wait_sem); | |
| 188 } else { | |
| 189 retval = SDL_SemWaitTimeout(cond->wait_sem, ms); | |
| 190 } | |
| 191 | |
| 192 /* Let the signaler know we have completed the wait, otherwise | |
| 193 the signaler can race ahead and get the condition semaphore | |
| 194 if we are stopped between the mutex unlock and semaphore wait, | |
| 195 giving a deadlock. See the following URL for details: | |
| 196 http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html | |
| 197 */ | |
| 198 SDL_LockMutex(cond->lock); | |
| 199 if ( cond->signals > 0 ) { | |
| 200 /* If we timed out, we need to eat a condition signal */ | |
| 201 if ( retval > 0 ) { | |
| 202 SDL_SemWait(cond->wait_sem); | |
| 203 } | |
| 204 /* We always notify the signal thread that we are done */ | |
| 205 SDL_SemPost(cond->wait_done); | |
| 206 | |
| 207 /* Signal handshake complete */ | |
| 208 --cond->signals; | |
| 209 } | |
| 210 --cond->waiting; | |
| 211 SDL_UnlockMutex(cond->lock); | |
| 212 | |
| 213 /* Lock the mutex, as is required by condition variable semantics */ | |
| 214 SDL_LockMutex(mutex); | |
| 215 | |
| 216 return retval; | |
| 217 } | |
| 218 | |
| 219 /* Wait on the condition variable forever */ | |
| 220 int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex) | |
| 221 { | |
| 222 return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT); | |
| 223 } |