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/* An implementation of condition variables using semaphores and mutexes */
24/*
25 This implementation borrows heavily from the BeOS condition variable
26 implementation, written by Christopher Tate and Owen Smith. Thanks!
27 */
28
29#include "SDL_thread.h"
30
32{
36 SDL_sem *wait_sem;
37 SDL_sem *wait_done;
38};
39
40/* Create a condition variable */
43{
44 SDL_cond *cond;
45
46 cond = (SDL_cond *) SDL_malloc(sizeof(SDL_cond));
47 if (cond) {
48 cond->lock = SDL_CreateMutex();
51 cond->waiting = cond->signals = 0;
52 if (!cond->lock || !cond->wait_sem || !cond->wait_done) {
53 SDL_DestroyCond(cond);
54 cond = NULL;
55 }
56 } else {
58 }
59 return (cond);
60}
61
62/* Destroy a condition variable */
63void
65{
66 if (cond) {
67 if (cond->wait_sem) {
69 }
70 if (cond->wait_done) {
72 }
73 if (cond->lock) {
75 }
76 SDL_free(cond);
77 }
78}
79
80/* Restart one of the threads that are waiting on the condition variable */
81int
83{
84 if (!cond) {
85 return SDL_SetError("Passed a NULL condition variable");
86 }
87
88 /* If there are waiting threads not already signalled, then
89 signal the condition and wait for the thread to respond.
90 */
91 SDL_LockMutex(cond->lock);
92 if (cond->waiting > cond->signals) {
93 ++cond->signals;
94 SDL_SemPost(cond->wait_sem);
95 SDL_UnlockMutex(cond->lock);
97 } else {
98 SDL_UnlockMutex(cond->lock);
99 }
100
101 return 0;
102}
103
104/* Restart all threads that are waiting on the condition variable */
105int
107{
108 if (!cond) {
109 return SDL_SetError("Passed a NULL condition variable");
110 }
111
112 /* If there are waiting threads not already signalled, then
113 signal the condition and wait for the thread to respond.
114 */
115 SDL_LockMutex(cond->lock);
116 if (cond->waiting > cond->signals) {
117 int i, num_waiting;
118
119 num_waiting = (cond->waiting - cond->signals);
120 cond->signals = cond->waiting;
121 for (i = 0; i < num_waiting; ++i) {
122 SDL_SemPost(cond->wait_sem);
123 }
124 /* Now all released threads are blocked here, waiting for us.
125 Collect them all (and win fabulous prizes!) :-)
126 */
127 SDL_UnlockMutex(cond->lock);
128 for (i = 0; i < num_waiting; ++i) {
129 SDL_SemWait(cond->wait_done);
130 }
131 } else {
132 SDL_UnlockMutex(cond->lock);
133 }
134
135 return 0;
136}
137
138/* Wait on the condition variable for at most 'ms' milliseconds.
139 The mutex must be locked before entering this function!
140 The mutex is unlocked during the wait, and locked again after the wait.
141
142Typical use:
143
144Thread A:
145 SDL_LockMutex(lock);
146 while ( ! condition ) {
147 SDL_CondWait(cond, lock);
148 }
149 SDL_UnlockMutex(lock);
150
151Thread B:
152 SDL_LockMutex(lock);
153 ...
154 condition = true;
155 ...
156 SDL_CondSignal(cond);
157 SDL_UnlockMutex(lock);
158 */
159int
161{
162 int retval;
163
164 if (!cond) {
165 return SDL_SetError("Passed a NULL condition variable");
166 }
167
168 /* Obtain the protection mutex, and increment the number of waiters.
169 This allows the signal mechanism to only perform a signal if there
170 are waiting threads.
171 */
172 SDL_LockMutex(cond->lock);
173 ++cond->waiting;
174 SDL_UnlockMutex(cond->lock);
175
176 /* Unlock the mutex, as is required by condition variable semantics */
178
179 /* Wait for a signal */
180 if (ms == SDL_MUTEX_MAXWAIT) {
181 retval = SDL_SemWait(cond->wait_sem);
182 } else {
184 }
185
186 /* Let the signaler know we have completed the wait, otherwise
187 the signaler can race ahead and get the condition semaphore
188 if we are stopped between the mutex unlock and semaphore wait,
189 giving a deadlock. See the following URL for details:
190 http://web.archive.org/web/20010914175514/http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html#Workshop
191 */
192 SDL_LockMutex(cond->lock);
193 if (cond->signals > 0) {
194 /* If we timed out, we need to eat a condition signal */
195 if (retval > 0) {
196 SDL_SemWait(cond->wait_sem);
197 }
198 /* We always notify the signal thread that we are done */
199 SDL_SemPost(cond->wait_done);
200
201 /* Signal handshake complete */
202 --cond->signals;
203 }
204 --cond->waiting;
205 SDL_UnlockMutex(cond->lock);
206
207 /* Lock the mutex, as is required by condition variable semantics */
209
210 return retval;
211}
212
213/* Wait on the condition variable forever */
214int
216{
218}
219
220/* 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