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 #include <errno.h>
24 #include <pthread.h>
25 
26 #include "SDL_thread.h"
27 
28 #if !SDL_THREAD_PTHREAD_RECURSIVE_MUTEX && \
29     !SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP
30 #define FAKE_RECURSIVE_MUTEX 1
31 #endif
32 
33 struct SDL_mutex
34 {
35     pthread_mutex_t id;
36 #if FAKE_RECURSIVE_MUTEX
37     int recursive;
38     pthread_t owner;
39 #endif
40 };
41 
42 SDL_mutex *
SDL_CreateMutex(void)43 SDL_CreateMutex(void)
44 {
45     SDL_mutex *mutex;
46     pthread_mutexattr_t attr;
47 
48     /* Allocate the structure */
49     mutex = (SDL_mutex *) SDL_calloc(1, sizeof(*mutex));
50     if (mutex) {
51         pthread_mutexattr_init(&attr);
52 #if SDL_THREAD_PTHREAD_RECURSIVE_MUTEX
53         pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
54 #elif SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP
55         pthread_mutexattr_setkind_np(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
56 #else
57         /* No extra attributes necessary */
58 #endif
59         if (pthread_mutex_init(&mutex->id, &attr) != 0) {
60             SDL_SetError("pthread_mutex_init() failed");
61             SDL_free(mutex);
62             mutex = NULL;
63         }
64     } else {
65         SDL_OutOfMemory();
66     }
67     return (mutex);
68 }
69 
70 void
SDL_DestroyMutex(SDL_mutex * mutex)71 SDL_DestroyMutex(SDL_mutex * mutex)
72 {
73     if (mutex) {
74         pthread_mutex_destroy(&mutex->id);
75         SDL_free(mutex);
76     }
77 }
78 
79 /* Lock the mutex */
80 int
SDL_LockMutex(SDL_mutex * mutex)81 SDL_LockMutex(SDL_mutex * mutex)
82 {
83 #if FAKE_RECURSIVE_MUTEX
84     pthread_t this_thread;
85 #endif
86 
87     if (mutex == NULL) {
88         return SDL_SetError("Passed a NULL mutex");
89     }
90 
91 #if FAKE_RECURSIVE_MUTEX
92     this_thread = pthread_self();
93     if (mutex->owner == this_thread) {
94         ++mutex->recursive;
95     } else {
96         /* The order of operations is important.
97            We set the locking thread id after we obtain the lock
98            so unlocks from other threads will fail.
99          */
100         if (pthread_mutex_lock(&mutex->id) == 0) {
101             mutex->owner = this_thread;
102             mutex->recursive = 0;
103         } else {
104             return SDL_SetError("pthread_mutex_lock() failed");
105         }
106     }
107 #else
108     if (pthread_mutex_lock(&mutex->id) != 0) {
109         return SDL_SetError("pthread_mutex_lock() failed");
110     }
111 #endif
112     return 0;
113 }
114 
115 int
SDL_TryLockMutex(SDL_mutex * mutex)116 SDL_TryLockMutex(SDL_mutex * mutex)
117 {
118     int retval;
119     int result;
120 #if FAKE_RECURSIVE_MUTEX
121     pthread_t this_thread;
122 #endif
123 
124     if (mutex == NULL) {
125         return SDL_SetError("Passed a NULL mutex");
126     }
127 
128     retval = 0;
129 #if FAKE_RECURSIVE_MUTEX
130     this_thread = pthread_self();
131     if (mutex->owner == this_thread) {
132         ++mutex->recursive;
133     } else {
134         /* The order of operations is important.
135          We set the locking thread id after we obtain the lock
136          so unlocks from other threads will fail.
137          */
138         result = pthread_mutex_trylock(&mutex->id);
139         if (result == 0) {
140             mutex->owner = this_thread;
141             mutex->recursive = 0;
142         } else if (result == EBUSY) {
143             retval = SDL_MUTEX_TIMEDOUT;
144         } else {
145             retval = SDL_SetError("pthread_mutex_trylock() failed");
146         }
147     }
148 #else
149     result = pthread_mutex_trylock(&mutex->id);
150     if (result != 0) {
151         if (result == EBUSY) {
152             retval = SDL_MUTEX_TIMEDOUT;
153         } else {
154             retval = SDL_SetError("pthread_mutex_trylock() failed");
155         }
156     }
157 #endif
158     return retval;
159 }
160 
161 int
SDL_UnlockMutex(SDL_mutex * mutex)162 SDL_UnlockMutex(SDL_mutex * mutex)
163 {
164     if (mutex == NULL) {
165         return SDL_SetError("Passed a NULL mutex");
166     }
167 
168 #if FAKE_RECURSIVE_MUTEX
169     /* We can only unlock the mutex if we own it */
170     if (pthread_self() == mutex->owner) {
171         if (mutex->recursive) {
172             --mutex->recursive;
173         } else {
174             /* The order of operations is important.
175                First reset the owner so another thread doesn't lock
176                the mutex and set the ownership before we reset it,
177                then release the lock semaphore.
178              */
179             mutex->owner = 0;
180             pthread_mutex_unlock(&mutex->id);
181         }
182     } else {
183         return SDL_SetError("mutex not owned by this thread");
184     }
185 
186 #else
187     if (pthread_mutex_unlock(&mutex->id) != 0) {
188         return SDL_SetError("pthread_mutex_unlock() failed");
189     }
190 #endif /* FAKE_RECURSIVE_MUTEX */
191 
192     return 0;
193 }
194 
195 /* vi: set ts=4 sw=4 expandtab: */
196