SDL  2.0
SDL_sysmutex.c
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1 /*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2018 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 
29 struct SDL_mutex
30 {
31  int recursive;
33  SDL_sem *sem;
34 };
35 
36 /* Create a mutex */
37 SDL_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 */
46  mutex->sem = SDL_CreateSemaphore(1);
47  mutex->recursive = 0;
48  mutex->owner = 0;
49  if (!mutex->sem) {
50  SDL_free(mutex);
51  mutex = NULL;
52  }
53  } else {
55  }
56  return mutex;
57 }
58 
59 /* Free the mutex */
60 void
62 {
63  if (mutex) {
64  if (mutex->sem) {
65  SDL_DestroySemaphore(mutex->sem);
66  }
67  SDL_free(mutex);
68  }
69 }
70 
71 /* Lock the mutex */
72 int
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) {
86  ++mutex->recursive;
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  */
92  SDL_SemWait(mutex->sem);
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 */
102 int
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  */
123  retval = SDL_SemWait(mutex->sem);
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 */
135 int
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;
159  SDL_SemPost(mutex->sem);
160  }
161  return 0;
162 #endif /* SDL_THREADS_DISABLED */
163 }
164 
165 /* vi: set ts=4 sw=4 expandtab: */
#define SDL_ThreadID
int SDL_TryLockMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:103
int SDL_mutexV(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:136
#define SDL_CreateSemaphore
int SDL_LockMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:73
static SDL_mutex * mutex
Definition: testlock.c:23
#define SDL_SemPost
SDL_bool retval
void SDL_DestroyMutex(SDL_mutex *mutex)
Definition: SDL_sysmutex.c:61
#define SDL_free
SDL_mutex * SDL_CreateMutex(void)
Definition: SDL_sysmutex.c:38
#define NULL
Definition: begin_code.h:164
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
#define SDL_SetError
SDL_threadID owner
Definition: SDL_sysmutex.c:32
#define SDL_SemWait
#define SDL_DestroySemaphore
#define SDL_malloc
int recursive
Definition: SDL_sysmutex.c:31
SDL_sem * sem
Definition: SDL_sysmutex.c:33
unsigned long SDL_threadID
Definition: SDL_thread.h:49