SDL  2.0
SDL_syssem.c
Go to the documentation of this file.
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 semaphores using mutexes and condition variables */
24 
25 #include "SDL_timer.h"
26 #include "SDL_thread.h"
27 #include "SDL_systhread_c.h"
28 
29 
30 #if SDL_THREADS_DISABLED
31 
32 SDL_sem *
33 SDL_CreateSemaphore(Uint32 initial_value)
34 {
35  SDL_SetError("SDL not built with thread support");
36  return (SDL_sem *) 0;
37 }
38 
39 void
40 SDL_DestroySemaphore(SDL_sem * sem)
41 {
42 }
43 
44 int
45 SDL_SemTryWait(SDL_sem * sem)
46 {
47  return SDL_SetError("SDL not built with thread support");
48 }
49 
50 int
52 {
53  return SDL_SetError("SDL not built with thread support");
54 }
55 
56 int
57 SDL_SemWait(SDL_sem * sem)
58 {
59  return SDL_SetError("SDL not built with thread support");
60 }
61 
62 Uint32
63 SDL_SemValue(SDL_sem * sem)
64 {
65  return 0;
66 }
67 
68 int
69 SDL_SemPost(SDL_sem * sem)
70 {
71  return SDL_SetError("SDL not built with thread support");
72 }
73 
74 #else
75 
77 {
82 };
83 
84 SDL_sem *
86 {
87  SDL_sem *sem;
88 
89  sem = (SDL_sem *) SDL_malloc(sizeof(*sem));
90  if (!sem) {
92  return NULL;
93  }
94  sem->count = initial_value;
95  sem->waiters_count = 0;
96 
97  sem->count_lock = SDL_CreateMutex();
98  sem->count_nonzero = SDL_CreateCond();
99  if (!sem->count_lock || !sem->count_nonzero) {
101  return NULL;
102  }
103 
104  return sem;
105 }
106 
107 /* WARNING:
108  You cannot call this function when another thread is using the semaphore.
109 */
110 void
112 {
113  if (sem) {
114  sem->count = 0xFFFFFFFF;
115  while (sem->waiters_count > 0) {
116  SDL_CondSignal(sem->count_nonzero);
117  SDL_Delay(10);
118  }
119  SDL_DestroyCond(sem->count_nonzero);
120  if (sem->count_lock) {
121  SDL_LockMutex(sem->count_lock);
122  SDL_UnlockMutex(sem->count_lock);
123  SDL_DestroyMutex(sem->count_lock);
124  }
125  SDL_free(sem);
126  }
127 }
128 
129 int
130 SDL_SemTryWait(SDL_sem * sem)
131 {
132  int retval;
133 
134  if (!sem) {
135  return SDL_SetError("Passed a NULL semaphore");
136  }
137 
138  retval = SDL_MUTEX_TIMEDOUT;
139  SDL_LockMutex(sem->count_lock);
140  if (sem->count > 0) {
141  --sem->count;
142  retval = 0;
143  }
144  SDL_UnlockMutex(sem->count_lock);
145 
146  return retval;
147 }
148 
149 int
151 {
152  int retval;
153 
154  if (!sem) {
155  return SDL_SetError("Passed a NULL semaphore");
156  }
157 
158  /* A timeout of 0 is an easy case */
159  if (timeout == 0) {
160  return SDL_SemTryWait(sem);
161  }
162 
163  SDL_LockMutex(sem->count_lock);
164  ++sem->waiters_count;
165  retval = 0;
166  while ((sem->count == 0) && (retval != SDL_MUTEX_TIMEDOUT)) {
167  retval = SDL_CondWaitTimeout(sem->count_nonzero,
168  sem->count_lock, timeout);
169  }
170  --sem->waiters_count;
171  if (retval == 0) {
172  --sem->count;
173  }
174  SDL_UnlockMutex(sem->count_lock);
175 
176  return retval;
177 }
178 
179 int
180 SDL_SemWait(SDL_sem * sem)
181 {
183 }
184 
185 Uint32
186 SDL_SemValue(SDL_sem * sem)
187 {
188  Uint32 value;
189 
190  value = 0;
191  if (sem) {
192  SDL_LockMutex(sem->count_lock);
193  value = sem->count;
194  SDL_UnlockMutex(sem->count_lock);
195  }
196  return value;
197 }
198 
199 int
200 SDL_SemPost(SDL_sem * sem)
201 {
202  if (!sem) {
203  return SDL_SetError("Passed a NULL semaphore");
204  }
205 
206  SDL_LockMutex(sem->count_lock);
207  if (sem->waiters_count > 0) {
208  SDL_CondSignal(sem->count_nonzero);
209  }
210  ++sem->count;
211  SDL_UnlockMutex(sem->count_lock);
212 
213  return 0;
214 }
215 
216 #endif /* SDL_THREADS_DISABLED */
217 /* vi: set ts=4 sw=4 expandtab: */
#define SDL_LockMutex
SDL_cond * count_nonzero
Definition: SDL_syssem.c:81
Uint32 waiters_count
Definition: SDL_syssem.c:79
#define SDL_CreateMutex
#define SDL_DestroyCond
uint32_t Uint32
Definition: SDL_stdinc.h:181
#define SDL_CondSignal
SDL_mutex * count_lock
Definition: SDL_syssem.c:80
int SDL_SemPost(SDL_sem *sem)
Definition: SDL_syssem.c:200
static SDL_sem * sem
Definition: testsem.c:23
#define SDL_MUTEX_TIMEDOUT
Definition: SDL_mutex.h:44
SDL_bool retval
#define SDL_MUTEX_MAXWAIT
Definition: SDL_mutex.h:49
#define SDL_CondWaitTimeout
int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
Definition: SDL_syssem.c:150
int SDL_SemTryWait(SDL_sem *sem)
Definition: SDL_syssem.c:130
#define SDL_free
int SDL_SemWait(SDL_sem *sem)
Definition: SDL_syssem.c:180
GLsizei const GLfloat * value
#define SDL_CreateCond
Uint32 count
Definition: SDL_syssem.c:78
#define SDL_Delay
#define NULL
Definition: begin_code.h:164
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
#define SDL_SetError
Uint32 SDL_SemValue(SDL_sem *sem)
Definition: SDL_syssem.c:186
#define SDL_DestroyMutex
GLbitfield GLuint64 timeout
#define SDL_UnlockMutex
#define SDL_malloc
void SDL_DestroySemaphore(SDL_sem *sem)
Definition: SDL_syssem.c:111
SDL_sem * SDL_CreateSemaphore(Uint32 initial_value)
Definition: SDL_syssem.c:85