SDL

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/*
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  Simple DirectMedia Layer
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  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
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  This software is provided 'as-is', without any express or implied
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  warranty.  In no event will the authors be held liable for any damages
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  arising from the use of this software.
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  Permission is granted to anyone to use this software for any purpose,
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  including commercial applications, and to alter it and redistribute it
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  freely, subject to the following restrictions:
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  1. The origin of this software must not be misrepresented; you must not
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     claim that you wrote the original software. If you use this software
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     in a product, an acknowledgment in the product documentation would be
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     appreciated but is not required.
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  2. Altered source versions must be plainly marked as such, and must not be
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     misrepresented as being the original software.
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  3. This notice may not be removed or altered from any source distribution.
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*/
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#include "SDL_internal.h"
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// An implementation of mutexes using semaphores
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#include "SDL_systhread_c.h"
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struct SDL_Mutex
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{
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    int recursive;
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    SDL_ThreadID owner;
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    SDL_Semaphore *sem;
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};
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SDL_Mutex *SDL_CreateMutex(void)
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{
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    SDL_Mutex *mutex = (SDL_Mutex *)SDL_calloc(1, sizeof(*mutex));
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#ifndef SDL_THREADS_DISABLED
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    if (mutex) {
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        // Create the mutex semaphore, with initial value 1
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        mutex->sem = SDL_CreateSemaphore(1);
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        mutex->recursive = 0;
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        mutex->owner = 0;
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        if (!mutex->sem) {
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            SDL_free(mutex);
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            mutex = NULL;
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        }
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    }
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#endif // !SDL_THREADS_DISABLED
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    return mutex;
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}
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void SDL_DestroyMutex(SDL_Mutex *mutex)
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{
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    if (mutex) {
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        if (mutex->sem) {
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            SDL_DestroySemaphore(mutex->sem);
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        }
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        SDL_free(mutex);
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    }
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}
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void SDL_LockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
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{
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#ifndef SDL_THREADS_DISABLED
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    if (mutex != NULL) {
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        SDL_ThreadID this_thread = SDL_GetCurrentThreadID();
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        if (mutex->owner == this_thread) {
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            ++mutex->recursive;
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        } else {
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            /* The order of operations is important.
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               We set the locking thread id after we obtain the lock
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               so unlocks from other threads will fail.
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             */
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            SDL_WaitSemaphore(mutex->sem);
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            mutex->owner = this_thread;
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            mutex->recursive = 0;
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        }
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    }
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#endif // SDL_THREADS_DISABLED
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}
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SDL_bool SDL_TryLockMutex(SDL_Mutex *mutex)
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{
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    bool result = true;
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#ifndef SDL_THREADS_DISABLED
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    if (mutex) {
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        SDL_ThreadID this_thread = SDL_GetCurrentThreadID();
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        if (mutex->owner == this_thread) {
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            ++mutex->recursive;
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        } else {
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            /* The order of operations is important.
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               We set the locking thread id after we obtain the lock
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               so unlocks from other threads will fail.
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             */
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            result = SDL_TryWaitSemaphore(mutex->sem);
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            if (result) {
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                mutex->owner = this_thread;
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                mutex->recursive = 0;
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            }
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        }
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    }
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#endif // SDL_THREADS_DISABLED
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    return result;
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}
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void SDL_UnlockMutex(SDL_Mutex *mutex) SDL_NO_THREAD_SAFETY_ANALYSIS  // clang doesn't know about NULL mutexes
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{
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#ifndef SDL_THREADS_DISABLED
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    if (mutex != NULL) {
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        // If we don't own the mutex, we can't unlock it
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        if (SDL_GetCurrentThreadID() != mutex->owner) {
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            SDL_assert(!"Tried to unlock a mutex we don't own!");
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            return; // (undefined behavior!) SDL_SetError("mutex not owned by this thread");
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        }
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        if (mutex->recursive) {
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            --mutex->recursive;
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        } else {
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            /* The order of operations is important.
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               First reset the owner so another thread doesn't lock
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               the mutex and set the ownership before we reset it,
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               then release the lock semaphore.
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             */
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            mutex->owner = 0;
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            SDL_SignalSemaphore(mutex->sem);
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        }
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    }
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#endif // SDL_THREADS_DISABLED
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}
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