SDL 2.0
SDL_syscond.c
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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#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
33struct SDL_cond
34{
36 int waiting;
37 int signals;
38 SDL_sem *wait_sem;
39 SDL_sem *wait_done;
40};
41
42/* Create a condition variable */
45{
46 SDL_cond *cond;
47
48 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
49 if (cond) {
50 cond->lock = SDL_CreateMutex();
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 */
65void
67{
68 if (cond) {
69 if (cond->wait_sem) {
71 }
72 if (cond->wait_done) {
74 }
75 if (cond->lock) {
77 }
78 SDL_free(cond);
79 }
80}
81
82/* Restart one of the threads that are waiting on the condition variable */
83int
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);
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 */
107int
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
144Typical use:
145
146Thread A:
147 SDL_LockMutex(lock);
148 while ( ! condition ) {
149 SDL_CondWait(cond, lock);
150 }
151 SDL_UnlockMutex(lock);
152
153Thread B:
154 SDL_LockMutex(lock);
155 ...
156 condition = true;
157 ...
158 SDL_CondSignal(cond);
159 SDL_UnlockMutex(lock);
160 */
161int
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 */
180
181 /* Wait for a signal */
182 if (ms == SDL_MUTEX_MAXWAIT) {
183 retval = SDL_SemWait(cond->wait_sem);
184 } else {
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 */
211
212 return retval;
213}
214
215/* Wait on the condition variable forever */
216int
218{
220}
221
222#endif /* SDL_THREAD_PSP */
223
224/* vi: set ts=4 sw=4 expandtab: */
#define SDL_SetError
#define SDL_SemPost
#define SDL_SemWait
#define SDL_LockMutex
#define SDL_malloc
#define SDL_SemWaitTimeout
#define SDL_DestroySemaphore
#define SDL_CreateMutex
#define SDL_free
#define SDL_CreateSemaphore
#define SDL_DestroyMutex
#define SDL_UnlockMutex
#define SDL_OutOfMemory()
Definition: SDL_error.h:52
#define SDL_MUTEX_MAXWAIT
Definition: SDL_mutex.h:49
uint32_t Uint32
Definition: SDL_stdinc.h:203
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:167
SDL_cond * SDL_CreateCond(void)
Definition: SDL_syscond.c:42
int SDL_CondBroadcast(SDL_cond *cond)
Definition: SDL_syscond.c:106
int SDL_CondWaitTimeout(SDL_cond *cond, SDL_mutex *mutex, Uint32 ms)
Definition: SDL_syscond.c:160
int SDL_CondSignal(SDL_cond *cond)
Definition: SDL_syscond.c:82
void SDL_DestroyCond(SDL_cond *cond)
Definition: SDL_syscond.c:64
int SDL_CondWait(SDL_cond *cond, SDL_mutex *mutex)
Definition: SDL_syscond.c:215
SDL_sem * wait_done
Definition: SDL_syscond.c:37
SDL_mutex * lock
Definition: SDL_syscond.c:33
int waiting
Definition: SDL_syscond.c:34
int signals
Definition: SDL_syscond.c:35
SDL_sem * wait_sem
Definition: SDL_syscond.c:36
SDL_bool retval
static SDL_mutex * mutex
Definition: testlock.c:23