1 /*
2 SDL - Simple DirectMedia Layer
3 Copyright (C) 1997-2012 Sam Lantinga
4
5 This library is free software; you can redistribute it and/or
6 modify it under the terms of the GNU Lesser General Public
7 License as published by the Free Software Foundation; either
8 version 2.1 of the License, or (at your option) any later version.
9
10 This library is distributed in the hope that it will be useful,
11 but WITHOUT ANY WARRANTY; without even the implied warranty of
12 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 Lesser General Public License for more details.
14
15 You should have received a copy of the GNU Lesser General Public
16 License along with this library; if not, write to the Free Software
17 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
18
19 Sam Lantinga
20 slouken@libsdl.org
21 */
22 #include "SDL_config.h"
23
24 /* An implementation of semaphores using mutexes and condition variables */
25
26 #include "SDL_timer.h"
27 #include "SDL_thread.h"
28 #include "SDL_systhread_c.h"
29
30
31 #if SDL_THREADS_DISABLED
32
SDL_CreateSemaphore(Uint32 initial_value)33 SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)
34 {
35 SDL_SetError("SDL not configured with thread support");
36 return (SDL_sem *)0;
37 }
38
SDL_DestroySemaphore(SDL_sem * sem)39 void SDL_DestroySemaphore(SDL_sem *sem)
40 {
41 return;
42 }
43
SDL_SemTryWait(SDL_sem * sem)44 int SDL_SemTryWait(SDL_sem *sem)
45 {
46 SDL_SetError("SDL not configured with thread support");
47 return -1;
48 }
49
SDL_SemWaitTimeout(SDL_sem * sem,Uint32 timeout)50 int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
51 {
52 SDL_SetError("SDL not configured with thread support");
53 return -1;
54 }
55
SDL_SemWait(SDL_sem * sem)56 int SDL_SemWait(SDL_sem *sem)
57 {
58 SDL_SetError("SDL not configured with thread support");
59 return -1;
60 }
61
SDL_SemValue(SDL_sem * sem)62 Uint32 SDL_SemValue(SDL_sem *sem)
63 {
64 return 0;
65 }
66
SDL_SemPost(SDL_sem * sem)67 int SDL_SemPost(SDL_sem *sem)
68 {
69 SDL_SetError("SDL not configured with thread support");
70 return -1;
71 }
72
73 #else
74
75 struct SDL_semaphore
76 {
77 Uint32 count;
78 Uint32 waiters_count;
79 SDL_mutex *count_lock;
80 SDL_cond *count_nonzero;
81 };
82
SDL_CreateSemaphore(Uint32 initial_value)83 SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)
84 {
85 SDL_sem *sem;
86
87 sem = (SDL_sem *)SDL_malloc(sizeof(*sem));
88 if ( ! sem ) {
89 SDL_OutOfMemory();
90 return NULL;
91 }
92 sem->count = initial_value;
93 sem->waiters_count = 0;
94
95 sem->count_lock = SDL_CreateMutex();
96 sem->count_nonzero = SDL_CreateCond();
97 if ( ! sem->count_lock || ! sem->count_nonzero ) {
98 SDL_DestroySemaphore(sem);
99 return NULL;
100 }
101
102 return sem;
103 }
104
105 /* WARNING:
106 You cannot call this function when another thread is using the semaphore.
107 */
SDL_DestroySemaphore(SDL_sem * sem)108 void SDL_DestroySemaphore(SDL_sem *sem)
109 {
110 if ( sem ) {
111 sem->count = 0xFFFFFFFF;
112 while ( sem->waiters_count > 0) {
113 SDL_CondSignal(sem->count_nonzero);
114 SDL_Delay(10);
115 }
116 SDL_DestroyCond(sem->count_nonzero);
117 if ( sem->count_lock ) {
118 SDL_mutexP(sem->count_lock);
119 SDL_mutexV(sem->count_lock);
120 SDL_DestroyMutex(sem->count_lock);
121 }
122 SDL_free(sem);
123 }
124 }
125
SDL_SemTryWait(SDL_sem * sem)126 int SDL_SemTryWait(SDL_sem *sem)
127 {
128 int retval;
129
130 if ( ! sem ) {
131 SDL_SetError("Passed a NULL semaphore");
132 return -1;
133 }
134
135 retval = SDL_MUTEX_TIMEDOUT;
136 SDL_LockMutex(sem->count_lock);
137 if ( sem->count > 0 ) {
138 --sem->count;
139 retval = 0;
140 }
141 SDL_UnlockMutex(sem->count_lock);
142
143 return retval;
144 }
145
SDL_SemWaitTimeout(SDL_sem * sem,Uint32 timeout)146 int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
147 {
148 int retval;
149
150 if ( ! sem ) {
151 SDL_SetError("Passed a NULL semaphore");
152 return -1;
153 }
154
155 /* A timeout of 0 is an easy case */
156 if ( timeout == 0 ) {
157 return SDL_SemTryWait(sem);
158 }
159
160 SDL_LockMutex(sem->count_lock);
161 ++sem->waiters_count;
162 retval = 0;
163 while ( (sem->count == 0) && (retval != SDL_MUTEX_TIMEDOUT) ) {
164 retval = SDL_CondWaitTimeout(sem->count_nonzero,
165 sem->count_lock, timeout);
166 }
167 --sem->waiters_count;
168 if (retval == 0) {
169 --sem->count;
170 }
171 SDL_UnlockMutex(sem->count_lock);
172
173 return retval;
174 }
175
SDL_SemWait(SDL_sem * sem)176 int SDL_SemWait(SDL_sem *sem)
177 {
178 return SDL_SemWaitTimeout(sem, SDL_MUTEX_MAXWAIT);
179 }
180
SDL_SemValue(SDL_sem * sem)181 Uint32 SDL_SemValue(SDL_sem *sem)
182 {
183 Uint32 value;
184
185 value = 0;
186 if ( sem ) {
187 SDL_LockMutex(sem->count_lock);
188 value = sem->count;
189 SDL_UnlockMutex(sem->count_lock);
190 }
191 return value;
192 }
193
SDL_SemPost(SDL_sem * sem)194 int SDL_SemPost(SDL_sem *sem)
195 {
196 if ( ! sem ) {
197 SDL_SetError("Passed a NULL semaphore");
198 return -1;
199 }
200
201 SDL_LockMutex(sem->count_lock);
202 if ( sem->waiters_count > 0 ) {
203 SDL_CondSignal(sem->count_nonzero);
204 }
205 ++sem->count;
206 SDL_UnlockMutex(sem->count_lock);
207
208 return 0;
209 }
210
211 #endif /* SDL_THREADS_DISABLED */
212