SDL  2.0
SDL_syscond.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 #if SDL_THREAD_PSP
24 
25 /* An implementation of condition variables using semaphores and mutexes */
26 /*
27  This implementation borrows heavily from the BeOS condition variable
28  implementation, written by Christopher Tate and Owen Smith. Thanks!
29  */
30 
31 #include "SDL_thread.h"
32 
33 struct SDL_cond
34 {
35  SDL_mutex *lock;
36  int waiting;
37  int signals;
38  SDL_sem *wait_sem;
39  SDL_sem *wait_done;
40 };
41 
42 /* Create a condition variable */
43 SDL_cond *
44 SDL_CreateCond(void)
45 {
46  SDL_cond *cond;
47 
48  cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
49  if (cond) {
50  cond->lock = SDL_CreateMutex();
51  cond->wait_sem = SDL_CreateSemaphore(0);
52  cond->wait_done = SDL_CreateSemaphore(0);
53  cond->waiting = cond->signals = 0;
54  if (!cond->lock || !cond->wait_sem || !cond->wait_done) {
55  SDL_DestroyCond(cond);
56  cond = NULL;
57  }
58  } else {
60  }
61  return (cond);
62 }
63 
64 /* Destroy a condition variable */
65 void
67 {
68  if (cond) {
69  if (cond->wait_sem) {
71  }
72  if (cond->wait_done) {
74  }
75  if (cond->lock) {
76  SDL_DestroyMutex(cond->lock);
77  }
78  SDL_free(cond);
79  }
80 }
81 
82 /* Restart one of the threads that are waiting on the condition variable */
83 int
85 {
86  if (!cond) {
87  return SDL_SetError("Passed a NULL condition variable");
88  }
89 
90  /* If there are waiting threads not already signalled, then
91  signal the condition and wait for the thread to respond.
92  */
93  SDL_LockMutex(cond->lock);
94  if (cond->waiting > cond->signals) {
95  ++cond->signals;
96  SDL_SemPost(cond->wait_sem);
97  SDL_UnlockMutex(cond->lock);
98  SDL_SemWait(cond->wait_done);
99  } else {
100  SDL_UnlockMutex(cond->lock);
101  }
102 
103  return 0;
104 }
105 
106 /* Restart all threads that are waiting on the condition variable */
107 int
109 {
110  if (!cond) {
111  return SDL_SetError("Passed a NULL condition variable");
112  }
113 
114  /* If there are waiting threads not already signalled, then
115  signal the condition and wait for the thread to respond.
116  */
117  SDL_LockMutex(cond->lock);
118  if (cond->waiting > cond->signals) {
119  int i, num_waiting;
120 
121  num_waiting = (cond->waiting - cond->signals);
122  cond->signals = cond->waiting;
123  for (i = 0; i < num_waiting; ++i) {
124  SDL_SemPost(cond->wait_sem);
125  }
126  /* Now all released threads are blocked here, waiting for us.
127  Collect them all (and win fabulous prizes!) :-)
128  */
129  SDL_UnlockMutex(cond->lock);
130  for (i = 0; i < num_waiting; ++i) {
131  SDL_SemWait(cond->wait_done);
132  }
133  } else {
134  SDL_UnlockMutex(cond->lock);
135  }
136 
137  return 0;
138 }
139 
140 /* Wait on the condition variable for at most 'ms' milliseconds.
141  The mutex must be locked before entering this function!
142  The mutex is unlocked during the wait, and locked again after the wait.
143 
144 Typical use:
145 
146 Thread A:
147  SDL_LockMutex(lock);
148  while ( ! condition ) {
149  SDL_CondWait(cond, lock);
150  }
151  SDL_UnlockMutex(lock);
152 
153 Thread B:
154  SDL_LockMutex(lock);
155  ...
156  condition = true;
157  ...
158  SDL_CondSignal(cond);
159  SDL_UnlockMutex(lock);
160  */
161 int
163 {
164  int retval;
165 
166  if (!cond) {
167  return SDL_SetError("Passed a NULL condition variable");
168  }
169 
170  /* Obtain the protection mutex, and increment the number of waiters.
171  This allows the signal mechanism to only perform a signal if there
172  are waiting threads.
173  */
174  SDL_LockMutex(cond->lock);
175  ++cond->waiting;
176  SDL_UnlockMutex(cond->lock);
177 
178  /* Unlock the mutex, as is required by condition variable semantics */
179  SDL_UnlockMutex(mutex);
180 
181  /* Wait for a signal */
182  if (ms == SDL_MUTEX_MAXWAIT) {
183  retval = SDL_SemWait(cond->wait_sem);
184  } else {
185  retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
186  }
187 
188  /* Let the signaler know we have completed the wait, otherwise
189  the signaler can race ahead and get the condition semaphore
190  if we are stopped between the mutex unlock and semaphore wait,
191  giving a deadlock. See the following URL for details:
192  http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
193  */
194  SDL_LockMutex(cond->lock);
195  if (cond->signals > 0) {
196  /* If we timed out, we need to eat a condition signal */
197  if (retval > 0) {
198  SDL_SemWait(cond->wait_sem);
199  }
200  /* We always notify the signal thread that we are done */
201  SDL_SemPost(cond->wait_done);
202 
203  /* Signal handshake complete */
204  --cond->signals;
205  }
206  --cond->waiting;
207  SDL_UnlockMutex(cond->lock);
208 
209  /* Lock the mutex, as is required by condition variable semantics */
210  SDL_LockMutex(mutex);
211 
212  return retval;
213 }
214 
215 /* Wait on the condition variable forever */
216 int
217 SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex)
218 {
219  return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
220 }
221 
222 #endif /* SDL_THREAD_PSP */
223 
224 /* vi: set ts=4 sw=4 expandtab: */
#define SDL_LockMutex
int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
Definition: SDL_syscond.c:215
#define SDL_CreateSemaphore
SDL_mutex * lock
Definition: SDL_syscond.c:33
#define SDL_CreateMutex
int waiting
Definition: SDL_syscond.c:34
uint32_t Uint32
Definition: SDL_stdinc.h:181
static SDL_mutex * mutex
Definition: testlock.c:23
#define SDL_SemPost
SDL_cond * SDL_CreateCond(void)
Definition: SDL_syscond.c:42
SDL_bool retval
#define SDL_SemWaitTimeout
#define SDL_MUTEX_MAXWAIT
Definition: SDL_mutex.h:49
#define SDL_free
pthread_cond_t cond
Definition: SDL_syscond.c:34
int signals
Definition: SDL_syscond.c:35
return Display return Display Bool Bool int int int return Display XEvent Bool(*) XPointer return Display return Display Drawable _Xconst char unsigned int unsigned int return Display Pixmap Pixmap XColor XColor unsigned int unsigned int return Display _Xconst char char int char return Display Visual unsigned int int int char unsigned int unsigned int in i)
Definition: SDL_x11sym.h:50
#define NULL
Definition: begin_code.h:164
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
Definition: SDL_syscond.c:160
#define SDL_SetError
#define SDL_DestroyMutex
SDL_sem * wait_done
Definition: SDL_syscond.c:37
#define SDL_SemWait
#define SDL_DestroySemaphore
SDL_sem * wait_sem
Definition: SDL_syscond.c:36
#define SDL_UnlockMutex
#define SDL_malloc
int SDL_CondBroadcast(SDL_cond *cond)
Definition: SDL_syscond.c:106
int SDL_CondSignal(SDL_cond *cond)
Definition: SDL_syscond.c:82
void SDL_DestroyCond(SDL_cond *cond)
Definition: SDL_syscond.c:64