| 1 | /* |
| 2 | SDL - Simple DirectMedia Layer |
| 3 | Copyright (C) 1997-2009 Sam Lantinga |
| 4 | |
| 5 | This library is free software; you can redistribute it and/or |
| 6 | modify it under the terms of the GNU Lesser General Public |
| 7 | License as published by the Free Software Foundation; either |
| 8 | version 2.1 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 | Lesser General Public License for more details. |
| 14 | |
| 15 | You should have received a copy of the GNU Lesser General Public |
| 16 | License along with this library; if not, write to the Free Software |
| 17 | Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA |
| 18 | |
| 19 | Sam Lantinga |
| 20 | slouken@libsdl.org |
| 21 | */ |
| 22 | #include "SDL_config.h" |
| 23 | |
| 24 | /* An implementation of mutexes using semaphores */ |
| 25 | |
| 26 | #include "SDL_thread.h" |
| 27 | #include "SDL_systhread_c.h" |
| 28 | |
| 29 | |
| 30 | struct SDL_mutex { |
| 31 | int recursive; |
| 32 | Uint32 owner; |
| 33 | SDL_sem *sem; |
| 34 | }; |
| 35 | |
| 36 | /* Create a mutex */ |
| 37 | SDL_mutex *SDL_CreateMutex(void) |
| 38 | { |
| 39 | SDL_mutex *mutex; |
| 40 | |
| 41 | /* Allocate mutex memory */ |
| 42 | mutex = (SDL_mutex *)SDL_malloc(sizeof(*mutex)); |
| 43 | if ( mutex ) { |
| 44 | /* Create the mutex semaphore, with initial value 1 */ |
| 45 | mutex->sem = SDL_CreateSemaphore(1); |
| 46 | mutex->recursive = 0; |
| 47 | mutex->owner = 0; |
| 48 | if ( ! mutex->sem ) { |
| 49 | SDL_free(mutex); |
| 50 | mutex = NULL; |
| 51 | } |
| 52 | } else { |
| 53 | SDL_OutOfMemory(); |
| 54 | } |
| 55 | return mutex; |
| 56 | } |
| 57 | |
| 58 | /* Free the mutex */ |
| 59 | void SDL_DestroyMutex(SDL_mutex *mutex) |
| 60 | { |
| 61 | if ( mutex ) { |
| 62 | if ( mutex->sem ) { |
| 63 | SDL_DestroySemaphore(mutex->sem); |
| 64 | } |
| 65 | SDL_free(mutex); |
| 66 | } |
| 67 | } |
| 68 | |
| 69 | /* Lock the semaphore */ |
| 70 | int SDL_mutexP(SDL_mutex *mutex) |
| 71 | { |
| 72 | #if SDL_THREADS_DISABLED |
| 73 | return 0; |
| 74 | #else |
| 75 | Uint32 this_thread; |
| 76 | |
| 77 | if ( mutex == NULL ) { |
| 78 | SDL_SetError("Passed a NULL mutex"); |
| 79 | return -1; |
| 80 | } |
| 81 | |
| 82 | this_thread = SDL_ThreadID(); |
| 83 | if ( mutex->owner == this_thread ) { |
| 84 | ++mutex->recursive; |
| 85 | } else { |
| 86 | /* The order of operations is important. |
| 87 | We set the locking thread id after we obtain the lock |
| 88 | so unlocks from other threads will fail. |
| 89 | */ |
| 90 | SDL_SemWait(mutex->sem); |
| 91 | mutex->owner = this_thread; |
| 92 | mutex->recursive = 0; |
| 93 | } |
| 94 | |
| 95 | return 0; |
| 96 | #endif /* SDL_THREADS_DISABLED */ |
| 97 | } |
| 98 | |
| 99 | /* Unlock the mutex */ |
| 100 | int SDL_mutexV(SDL_mutex *mutex) |
| 101 | { |
| 102 | #if SDL_THREADS_DISABLED |
| 103 | return 0; |
| 104 | #else |
| 105 | if ( mutex == NULL ) { |
| 106 | SDL_SetError("Passed a NULL mutex"); |
| 107 | return -1; |
| 108 | } |
| 109 | |
| 110 | /* If we don't own the mutex, we can't unlock it */ |
| 111 | if ( SDL_ThreadID() != mutex->owner ) { |
| 112 | SDL_SetError("mutex not owned by this thread"); |
| 113 | return -1; |
| 114 | } |
| 115 | |
| 116 | if ( mutex->recursive ) { |
| 117 | --mutex->recursive; |
| 118 | } else { |
| 119 | /* The order of operations is important. |
| 120 | First reset the owner so another thread doesn't lock |
| 121 | the mutex and set the ownership before we reset it, |
| 122 | then release the lock semaphore. |
| 123 | */ |
| 124 | mutex->owner = 0; |
| 125 | SDL_SemPost(mutex->sem); |
| 126 | } |
| 127 | return 0; |
| 128 | #endif /* SDL_THREADS_DISABLED */ |
| 129 | } |