1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997-2006 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 */
SDL_CreateMutex(void)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 */
SDL_DestroyMutex(SDL_mutex * 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 */
SDL_mutexP(SDL_mutex * mutex)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 */
SDL_mutexV(SDL_mutex * 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 }
130