SDL_sysmutex.c revision 9682c8870b8ff5e4ac2e4c70b759f791c6f38c1f 
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
31struct SDL_mutex {
32	int recursive;
33	Uint32 owner;
34	spinlock_t mutex;
35};
36
37/* Create a mutex */
38SDL_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 */
55void SDL_DestroyMutex(SDL_mutex *mutex)
56{
57	if ( mutex ) {
58		SDL_free(mutex);
59	}
60}
61
62/* Lock the semaphore */
63int 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 */
93int 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