SDL 2.0
SDL_sysmutex.c
Go to the documentation of this file.
1/*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2019 Sam Lantinga <slouken@libsdl.org>
4
5 This software is provided 'as-is', without any express or implied
6 warranty. In no event will the authors be held liable for any damages
7 arising from the use of this software.
8
9 Permission is granted to anyone to use this software for any purpose,
10 including commercial applications, and to alter it and redistribute it
11 freely, subject to the following restrictions:
12
13 1. The origin of this software must not be misrepresented; you must not
14 claim that you wrote the original software. If you use this software
15 in a product, an acknowledgment in the product documentation would be
16 appreciated but is not required.
17 2. Altered source versions must be plainly marked as such, and must not be
18 misrepresented as being the original software.
19 3. This notice may not be removed or altered from any source distribution.
20*/
21#include "../../SDL_internal.h"
22
23/* An implementation of mutexes using semaphores */
24
25#include "SDL_thread.h"
26#include "SDL_systhread_c.h"
27
28
30{
33 SDL_sem *sem;
34};
35
36/* Create a mutex */
39{
41
42 /* Allocate mutex memory */
43 mutex = (SDL_mutex *) SDL_malloc(sizeof(*mutex));
44 if (mutex) {
45 /* Create the mutex semaphore, with initial value 1 */
47 mutex->recursive = 0;
48 mutex->owner = 0;
49 if (!mutex->sem) {
51 mutex = NULL;
52 }
53 } else {
55 }
56 return mutex;
57}
58
59/* Free the mutex */
60void
62{
63 if (mutex) {
64 if (mutex->sem) {
66 }
68 }
69}
70
71/* Lock the mutex */
72int
74{
75#if SDL_THREADS_DISABLED
76 return 0;
77#else
78 SDL_threadID this_thread;
79
80 if (mutex == NULL) {
81 return SDL_SetError("Passed a NULL mutex");
82 }
83
84 this_thread = SDL_ThreadID();
85 if (mutex->owner == this_thread) {
87 } else {
88 /* The order of operations is important.
89 We set the locking thread id after we obtain the lock
90 so unlocks from other threads will fail.
91 */
93 mutex->owner = this_thread;
94 mutex->recursive = 0;
95 }
96
97 return 0;
98#endif /* SDL_THREADS_DISABLED */
99}
100
101/* try Lock the mutex */
102int
104{
105#if SDL_THREADS_DISABLED
106 return 0;
107#else
108 int retval = 0;
109 SDL_threadID this_thread;
110
111 if (mutex == NULL) {
112 return SDL_SetError("Passed a NULL mutex");
113 }
114
115 this_thread = SDL_ThreadID();
116 if (mutex->owner == this_thread) {
117 ++mutex->recursive;
118 } else {
119 /* The order of operations is important.
120 We set the locking thread id after we obtain the lock
121 so unlocks from other threads will fail.
122 */
124 if (retval == 0) {
125 mutex->owner = this_thread;
126 mutex->recursive = 0;
127 }
128 }
129
130 return retval;
131#endif /* SDL_THREADS_DISABLED */
132}
133
134/* Unlock the mutex */
135int
137{
138#if SDL_THREADS_DISABLED
139 return 0;
140#else
141 if (mutex == NULL) {
142 return SDL_SetError("Passed a NULL mutex");
143 }
144
145 /* If we don't own the mutex, we can't unlock it */
146 if (SDL_ThreadID() != mutex->owner) {
147 return SDL_SetError("mutex not owned by this thread");
148 }
149
150 if (mutex->recursive) {
151 --mutex->recursive;
152 } else {
153 /* The order of operations is important.
154 First reset the owner so another thread doesn't lock
155 the mutex and set the ownership before we reset it,
156 then release the lock semaphore.
157 */
158 mutex->owner = 0;
160 }
161 return 0;
162#endif /* SDL_THREADS_DISABLED */
163}
164
165/* vi: set ts=4 sw=4 expandtab: */
#define SDL_SetError
#define SDL_SemPost
#define SDL_SemWait
#define SDL_malloc
#define SDL_ThreadID
#define SDL_DestroySemaphore
#define SDL_free
#define SDL_CreateSemaphore
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
unsigned long SDL_threadID
Definition: SDL_thread.h:49
#define NULL
Definition: begin_code.h:167
void SDL_DestroyMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:61
int SDL_mutexV(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:136
int SDL_LockMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:73
int SDL_TryLockMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:103
SDL_mutex * SDL_CreateMutex(void)
Definition: SDL_sysmutex.c:38
SDL_threadID owner
Definition: SDL_sysmutex.c:32
int recursive
Definition: SDL_sysmutex.c:31
SDL_sem * sem
Definition: SDL_sysmutex.c:33
SDL_bool retval
static SDL_mutex * mutex
Definition: testlock.c:23