1 /*
2 Simple DirectMedia Layer
3 Copyright (C) 1997-2020 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 *
SDL_CreateCond(void)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 {
59 SDL_OutOfMemory();
60 }
61 return (cond);
62 }
63
64 /* Destroy a condition variable */
65 void
SDL_DestroyCond(SDL_cond * cond)66 SDL_DestroyCond(SDL_cond * cond)
67 {
68 if (cond) {
69 if (cond->wait_sem) {
70 SDL_DestroySemaphore(cond->wait_sem);
71 }
72 if (cond->wait_done) {
73 SDL_DestroySemaphore(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
SDL_CondSignal(SDL_cond * cond)84 SDL_CondSignal(SDL_cond * cond)
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
SDL_CondBroadcast(SDL_cond * cond)108 SDL_CondBroadcast(SDL_cond * cond)
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
SDL_CondWaitTimeout(SDL_cond * cond,SDL_mutex * mutex,Uint32 ms)162 SDL_CondWaitTimeout(SDL_cond * cond, SDL_mutex * mutex, Uint32 ms)
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
SDL_CondWait(SDL_cond * cond,SDL_mutex * mutex)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: */
225