Atlas - SDL_sysmutex.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2018 Sam Lantinga <[email protected]>
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
33struct SDL_mutex
34{
35    pthread_mutex_t id;
36#if FAKE_RECURSIVE_MUTEX
37    int recursive;
38    pthread_t owner;
39#endif
40};
41
42SDL_mutex *
43SDL_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
70void
71SDL_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 */
80int
81SDL_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
115int
116SDL_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
161int
162SDL_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
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