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comparison src/thread/generic/SDL_sysmutex.c @ 0:74212992fb08

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Initial revision
author Sam Lantinga <slouken@lokigames.com>
date Thu, 26 Apr 2001 16:45:43 +0000
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children e8157fcb3114
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1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997, 1998, 1999, 2000, 2001 Sam Lantinga
4
5 This library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Library General Public
7 License as published by the Free Software Foundation; either
8 version 2 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 Library General Public License for more details.
14
15 You should have received a copy of the GNU Library General Public
16 License along with this library; if not, write to the Free
17 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18
19 Sam Lantinga
20 slouken@devolution.com
21 */
22
23 #ifdef SAVE_RCSID
24 static char rcsid =
25 "@(#) $Id$";
26 #endif
27
28 /* An implementation of mutexes using semaphores */
29
30 #include <stdio.h>
31 #include <stdlib.h>
32
33 #include "SDL_error.h"
34 #include "SDL_thread.h"
35 #include "SDL_systhread_c.h"
36
37
38 struct SDL_mutex {
39 int recursive;
40 Uint32 owner;
41 SDL_sem *sem;
42 };
43
44 /* Create a mutex */
45 SDL_mutex *SDL_CreateMutex(void)
46 {
47 SDL_mutex *mutex;
48
49 /* Allocate mutex memory */
50 mutex = (SDL_mutex *)malloc(sizeof(*mutex));
51 if ( mutex ) {
52 /* Create the mutex semaphore, with initial value 1 */
53 mutex->sem = SDL_CreateSemaphore(1);
54 mutex->recursive = 0;
55 mutex->owner = 0;
56 if ( ! mutex->sem ) {
57 free(mutex);
58 mutex = NULL;
59 }
60 } else {
61 SDL_OutOfMemory();
62 }
63 return mutex;
64 }
65
66 /* Free the mutex */
67 void SDL_DestroyMutex(SDL_mutex *mutex)
68 {
69 if ( mutex ) {
70 if ( mutex->sem ) {
71 SDL_DestroySemaphore(mutex->sem);
72 }
73 free(mutex);
74 }
75 }
76
77 /* Lock the semaphore */
78 int SDL_mutexP(SDL_mutex *mutex)
79 {
80 #ifdef DISABLE_THREADS
81 return 0;
82 #else
83 Uint32 this_thread;
84
85 if ( mutex == NULL ) {
86 SDL_SetError("Passed a NULL mutex");
87 return -1;
88 }
89
90 this_thread = SDL_ThreadID();
91 if ( mutex->owner == this_thread ) {
92 ++mutex->recursive;
93 } else {
94 /* The order of operations is important.
95 We set the locking thread id after we obtain the lock
96 so unlocks from other threads will fail.
97 */
98 SDL_SemWait(mutex->sem);
99 mutex->owner = this_thread;
100 mutex->recursive = 0;
101 }
102
103 return 0;
104 #endif /* DISABLE_THREADS */
105 }
106
107 /* Unlock the mutex */
108 int SDL_mutexV(SDL_mutex *mutex)
109 {
110 #ifdef DISABLE_THREADS
111 return 0;
112 #else
113 if ( mutex == NULL ) {
114 SDL_SetError("Passed a NULL mutex");
115 return -1;
116 }
117
118 /* If we don't own the mutex, we can't unlock it */
119 if ( SDL_ThreadID() != mutex->owner ) {
120 SDL_SetError("mutex not owned by this thread");
121 return -1;
122 }
123
124 if ( mutex->recursive ) {
125 --mutex->recursive;
126 } else {
127 /* The order of operations is important.
128 First reset the owner so another thread doesn't lock
129 the mutex and set the ownership before we reset it,
130 then release the lock semaphore.
131 */
132 mutex->owner = 0;
133 SDL_SemPost(mutex->sem);
134 }
135 return 0;
136 #endif /* DISABLE_THREADS */
137 }