Atlas - SDL_sysmutex.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 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_sysmutex_c.h"
27
28SDL_Mutex *SDL_CreateMutex(void)
29{
30    SDL_Mutex *mutex;
31    pthread_mutexattr_t attr;
32
33    // Allocate the structure
34    mutex = (SDL_Mutex *)SDL_calloc(1, sizeof(*mutex));
35    if (mutex) {
36        pthread_mutexattr_init(&attr);
37#ifdef SDL_THREAD_PTHREAD_RECURSIVE_MUTEX
38        pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
39#elif defined(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX_NP)
40        pthread_mutexattr_setkind_np(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
41#else
42        // No extra attributes necessary
43#endif
44        if (pthread_mutex_init(&mutex->id, &attr) != 0) {
45            SDL_SetError("pthread_mutex_init() failed");
46            SDL_free(mutex);
47            mutex = NULL;
48        }
49    }
50    return mutex;
51}
52
53void SDL_DestroyMutex(SDL_Mutex *mutex)
54{
55    if (mutex) {
56        pthread_mutex_destroy(&mutex->id);
57        SDL_free(mutex);
58    }
59}
60
61void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
62{
63    if (mutex) {
64#ifdef FAKE_RECURSIVE_MUTEX
65        pthread_t this_thread = pthread_self();
66        if (mutex->owner == this_thread) {
67            ++mutex->recursive;
68        } else {
69            /* The order of operations is important.
70               We set the locking thread id after we obtain the lock
71               so unlocks from other threads will fail.
72             */
73            const int rc = pthread_mutex_lock(&mutex->id);
74            SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
75            mutex->owner = this_thread;
76            mutex->recursive = 0;
77        }
78#else
79        const int rc = pthread_mutex_lock(&mutex->id);
80        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
81#endif
82    }
83}
84
85bool SDL_TryLockMutex(SDL_Mutex *mutex)
86{
87    bool result = true;
88
89    if (mutex) {
90#ifdef FAKE_RECURSIVE_MUTEX
91        pthread_t this_thread = pthread_self();
92        if (mutex->owner == this_thread) {
93            ++mutex->recursive;
94        } else {
95            /* The order of operations is important.
96               We set the locking thread id after we obtain the lock
97               so unlocks from other threads will fail.
98             */
99            const int rc = pthread_mutex_trylock(&mutex->id);
100            if (rc == 0) {
101                mutex->owner = this_thread;
102                mutex->recursive = 0;
103            } else if (rc == EBUSY) {
104                result = false;
105            } else {
106                SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
107                result = false;
108            }
109        }
110#else
111        const int rc = pthread_mutex_trylock(&mutex->id);
112        if (rc != 0) {
113            if (rc == EBUSY) {
114                result = false;
115            } else {
116                SDL_assert(!"Error trying to lock mutex");  // assume we're in a lot of trouble if this assert fails.
117                result = false;
118            }
119        }
120#endif
121    }
122
123    return result;
124}
125
126void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS // clang doesn't know about NULL mutexes
127{
128    if (mutex) {
129#ifdef FAKE_RECURSIVE_MUTEX
130        // We can only unlock the mutex if we own it
131        if (pthread_self() == mutex->owner) {
132            if (mutex->recursive) {
133                --mutex->recursive;
134            } else {
135                /* The order of operations is important.
136                   First reset the owner so another thread doesn't lock
137                   the mutex and set the ownership before we reset it,
138                   then release the lock semaphore.
139                 */
140                mutex->owner = 0;
141                pthread_mutex_unlock(&mutex->id);
142            }
143        } else {
144            SDL_SetError("mutex not owned by this thread");
145            return;
146        }
147
148#else
149        const int rc = pthread_mutex_unlock(&mutex->id);
150        SDL_assert(rc == 0);  // assume we're in a lot of trouble if this assert fails.
151#endif // FAKE_RECURSIVE_MUTEX
152    }
153}
154
155
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