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1 /*
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2 SDL - Simple DirectMedia Layer
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3 Copyright (C) 1997, 1998, 1999, 2000, 2001 Sam Lantinga
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4
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5 This library is free software; you can redistribute it and/or
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6 modify it under the terms of the GNU Library General Public
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7 License as published by the Free Software Foundation; either
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8 version 2 of the License, or (at your option) any later version.
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9
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10 This library is distributed in the hope that it will be useful,
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11 but WITHOUT ANY WARRANTY; without even the implied warranty of
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12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 Library General Public License for more details.
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14
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15 You should have received a copy of the GNU Library General Public
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16 License along with this library; if not, write to the Free
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17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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18
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19 Sam Lantinga
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20 slouken@devolution.com
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21 */
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22
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23 #ifdef SAVE_RCSID
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24 static char rcsid =
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25 "@(#) $Id$";
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26 #endif
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27
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28 /* An implementation of mutexes using semaphores */
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29
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30 #include <stdio.h>
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31 #include <stdlib.h>
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32
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33 #include "SDL_error.h"
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34 #include "SDL_thread.h"
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35 #include "SDL_systhread_c.h"
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36
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37
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38 struct SDL_mutex {
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39 int recursive;
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40 Uint32 owner;
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41 SDL_sem *sem;
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42 };
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43
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44 /* Create a mutex */
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45 SDL_mutex *SDL_CreateMutex(void)
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46 {
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47 SDL_mutex *mutex;
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48
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49 /* Allocate mutex memory */
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50 mutex = (SDL_mutex *)malloc(sizeof(*mutex));
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51 if ( mutex ) {
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52 /* Create the mutex semaphore, with initial value 1 */
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53 mutex->sem = SDL_CreateSemaphore(1);
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54 mutex->recursive = 0;
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55 mutex->owner = 0;
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56 if ( ! mutex->sem ) {
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57 free(mutex);
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58 mutex = NULL;
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59 }
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60 } else {
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61 SDL_OutOfMemory();
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62 }
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63 return mutex;
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64 }
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65
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66 /* Free the mutex */
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67 void SDL_DestroyMutex(SDL_mutex *mutex)
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68 {
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69 if ( mutex ) {
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70 if ( mutex->sem ) {
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71 SDL_DestroySemaphore(mutex->sem);
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72 }
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73 free(mutex);
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74 }
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75 }
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76
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77 /* Lock the semaphore */
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78 int SDL_mutexP(SDL_mutex *mutex)
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79 {
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80 #ifdef DISABLE_THREADS
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81 return 0;
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82 #else
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83 Uint32 this_thread;
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84
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85 if ( mutex == NULL ) {
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86 SDL_SetError("Passed a NULL mutex");
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87 return -1;
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88 }
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89
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90 this_thread = SDL_ThreadID();
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91 if ( mutex->owner == this_thread ) {
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92 ++mutex->recursive;
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93 } else {
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94 /* The order of operations is important.
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95 We set the locking thread id after we obtain the lock
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96 so unlocks from other threads will fail.
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97 */
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98 SDL_SemWait(mutex->sem);
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99 mutex->owner = this_thread;
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100 mutex->recursive = 0;
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101 }
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102
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103 return 0;
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104 #endif /* DISABLE_THREADS */
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105 }
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106
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107 /* Unlock the mutex */
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108 int SDL_mutexV(SDL_mutex *mutex)
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109 {
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110 #ifdef DISABLE_THREADS
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111 return 0;
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112 #else
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113 if ( mutex == NULL ) {
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114 SDL_SetError("Passed a NULL mutex");
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115 return -1;
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116 }
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117
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118 /* If we don't own the mutex, we can't unlock it */
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119 if ( SDL_ThreadID() != mutex->owner ) {
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120 SDL_SetError("mutex not owned by this thread");
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121 return -1;
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122 }
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123
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124 if ( mutex->recursive ) {
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125 --mutex->recursive;
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126 } else {
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127 /* The order of operations is important.
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128 First reset the owner so another thread doesn't lock
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129 the mutex and set the ownership before we reset it,
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130 then release the lock semaphore.
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131 */
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132 mutex->owner = 0;
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133 SDL_SemPost(mutex->sem);
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134 }
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135 return 0;
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136 #endif /* DISABLE_THREADS */
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137 }
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