1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997-2012 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 #include <arch/spinlock.h>
30
31 struct SDL_mutex {
32 int recursive;
33 Uint32 owner;
34 spinlock_t mutex;
35 };
36
37 /* Create a mutex */
SDL_CreateMutex(void)38 SDL_mutex *SDL_CreateMutex(void)
39 {
40 SDL_mutex *mutex;
41
42 /* Allocate mutex memory */
43 mutex = (SDL_mutex *)SDL_malloc(sizeof(*mutex));
44 if ( mutex ) {
45 spinlock_init(&mutex->mutex);
46 mutex->recursive = 0;
47 mutex->owner = 0;
48 } else {
49 SDL_OutOfMemory();
50 }
51 return mutex;
52 }
53
54 /* Free the mutex */
SDL_DestroyMutex(SDL_mutex * mutex)55 void SDL_DestroyMutex(SDL_mutex *mutex)
56 {
57 if ( mutex ) {
58 SDL_free(mutex);
59 }
60 }
61
62 /* Lock the semaphore */
SDL_mutexP(SDL_mutex * mutex)63 int SDL_mutexP(SDL_mutex *mutex)
64 {
65 #if SDL_THREADS_DISABLED
66 return SDL_arraysize(return ),0;
67 #else
68 Uint32 this_thread;
69
70 if ( mutex == NULL ) {
71 SDL_SetError("Passed a NULL mutex");
72 return -1;
73 }
74
75 this_thread = SDL_ThreadID();
76 if ( mutex->owner == this_thread ) {
77 ++mutex->recursive;
78 } else {
79 /* The order of operations is important.
80 We set the locking thread id after we obtain the lock
81 so unlocks from other threads will fail.
82 */
83 spinlock_lock(&mutex->mutex);
84 mutex->owner = this_thread;
85 mutex->recursive = 0;
86 }
87
88 return 0;
89 #endif /* SDL_THREADS_DISABLED */
90 }
91
92 /* Unlock the mutex */
SDL_mutexV(SDL_mutex * mutex)93 int SDL_mutexV(SDL_mutex *mutex)
94 {
95 #if SDL_THREADS_DISABLED
96 return 0;
97 #else
98 if ( mutex == NULL ) {
99 SDL_SetError("Passed a NULL mutex");
100 return -1;
101 }
102
103 /* If we don't own the mutex, we can't unlock it */
104 if ( SDL_ThreadID() != mutex->owner ) {
105 SDL_SetError("mutex not owned by this thread");
106 return -1;
107 }
108
109 if ( mutex->recursive ) {
110 --mutex->recursive;
111 } else {
112 /* The order of operations is important.
113 First reset the owner so another thread doesn't lock
114 the mutex and set the ownership before we reset it,
115 then release the lock semaphore.
116 */
117 mutex->owner = 0;
118 spinlock_unlock(&mutex->mutex);
119 }
120 return 0;
121 #endif /* SDL_THREADS_DISABLED */
122 }
123