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1 /* |
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2 SDL - Simple DirectMedia Layer |
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3 Copyright (C) 1997-2006 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 Lesser General Public |
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7 License as published by the Free Software Foundation; either |
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8 version 2.1 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 Lesser 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 Lesser General Public |
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16 License along with this library; if not, write to the Free Software |
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17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA |
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18 |
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19 Sam Lantinga |
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20 slouken@libsdl.org |
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21 */ |
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22 #include "SDL_config.h" |
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23 |
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24 /* An implementation of mutexes using semaphores */ |
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25 |
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26 #include "SDL_thread.h" |
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27 #include "SDL_systhread_c.h" |
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28 |
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29 |
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30 struct SDL_mutex { |
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31 int recursive; |
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32 Uint32 owner; |
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33 SDL_sem *sem; |
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34 }; |
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35 |
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36 /* Create a mutex */ |
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37 SDL_mutex *SDL_CreateMutex(void) |
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38 { |
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39 SDL_mutex *mutex; |
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40 |
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41 /* Allocate mutex memory */ |
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42 mutex = (SDL_mutex *)SDL_malloc(sizeof(*mutex)); |
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43 if ( mutex ) { |
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44 /* Create the mutex semaphore, with initial value 1 */ |
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45 mutex->sem = SDL_CreateSemaphore(1); |
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46 mutex->recursive = 0; |
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47 mutex->owner = 0; |
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48 if ( ! mutex->sem ) { |
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49 SDL_free(mutex); |
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50 mutex = NULL; |
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51 } |
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52 } else { |
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53 SDL_OutOfMemory(); |
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54 } |
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55 return mutex; |
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56 } |
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57 |
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58 /* Free the mutex */ |
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59 void SDL_DestroyMutex(SDL_mutex *mutex) |
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60 { |
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61 if ( mutex ) { |
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62 if ( mutex->sem ) { |
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63 SDL_DestroySemaphore(mutex->sem); |
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64 } |
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65 SDL_free(mutex); |
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66 } |
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67 } |
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68 |
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69 /* Lock the semaphore */ |
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70 int SDL_mutexP(SDL_mutex *mutex) |
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71 { |
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72 #if SDL_THREADS_DISABLED |
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73 return 0; |
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74 #else |
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75 Uint32 this_thread; |
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76 |
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77 if ( mutex == NULL ) { |
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78 SDL_SetError("Passed a NULL mutex"); |
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79 return -1; |
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80 } |
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81 |
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82 this_thread = SDL_ThreadID(); |
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83 if ( mutex->owner == this_thread ) { |
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84 ++mutex->recursive; |
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85 } else { |
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86 /* The order of operations is important. |
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87 We set the locking thread id after we obtain the lock |
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88 so unlocks from other threads will fail. |
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89 */ |
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90 SDL_SemWait(mutex->sem); |
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91 mutex->owner = this_thread; |
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92 mutex->recursive = 0; |
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93 } |
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94 |
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95 return 0; |
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96 #endif /* SDL_THREADS_DISABLED */ |
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97 } |
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98 |
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99 /* Unlock the mutex */ |
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100 int SDL_mutexV(SDL_mutex *mutex) |
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101 { |
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102 #if SDL_THREADS_DISABLED |
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103 return 0; |
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104 #else |
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105 if ( mutex == NULL ) { |
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106 SDL_SetError("Passed a NULL mutex"); |
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107 return -1; |
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108 } |
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109 |
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110 /* If we don't own the mutex, we can't unlock it */ |
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111 if ( SDL_ThreadID() != mutex->owner ) { |
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112 SDL_SetError("mutex not owned by this thread"); |
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113 return -1; |
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114 } |
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115 |
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116 if ( mutex->recursive ) { |
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117 --mutex->recursive; |
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118 } else { |
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119 /* The order of operations is important. |
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120 First reset the owner so another thread doesn't lock |
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121 the mutex and set the ownership before we reset it, |
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122 then release the lock semaphore. |
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123 */ |
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124 mutex->owner = 0; |
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125 SDL_SemPost(mutex->sem); |
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126 } |
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127 return 0; |
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128 #endif /* SDL_THREADS_DISABLED */ |
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129 } |