initial commit, 4.5 stable

thirdparty/sdl/thread/generic/SDL_syscond.c

@@ -0,0 +1,216 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2025 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "SDL_internal.h"
+
+// An implementation of condition variables using semaphores and mutexes
+/*
+   This implementation borrows heavily from the BeOS condition variable
+   implementation, written by Christopher Tate and Owen Smith.  Thanks!
+ */
+
+#include "../generic/SDL_syscond_c.h"
+
+/* If two implementations are to be compiled into SDL (the active one
+ * will be chosen at runtime), the function names need to be
+ * suffixed
+ */
+#ifndef SDL_THREAD_GENERIC_COND_SUFFIX
+#define SDL_CreateCondition_generic      SDL_CreateCondition
+#define SDL_DestroyCondition_generic     SDL_DestroyCondition
+#define SDL_SignalCondition_generic      SDL_SignalCondition
+#define SDL_BroadcastCondition_generic   SDL_BroadcastCondition
+#endif
+
+typedef struct SDL_cond_generic
+{
+    SDL_Semaphore *sem;
+    SDL_Semaphore *handshake_sem;
+    SDL_Semaphore *signal_sem;
+    int num_waiting;
+    int num_signals;
+} SDL_cond_generic;
+
+// Create a condition variable
+SDL_Condition *SDL_CreateCondition_generic(void)
+{
+    SDL_cond_generic *cond = (SDL_cond_generic *)SDL_calloc(1, sizeof(*cond));
+
+#ifndef SDL_THREADS_DISABLED
+    if (cond) {
+        cond->sem = SDL_CreateSemaphore(0);
+        cond->handshake_sem = SDL_CreateSemaphore(0);
+        cond->signal_sem = SDL_CreateSemaphore(1);
+        if (!cond->sem || !cond->handshake_sem || !cond->signal_sem) {
+            SDL_DestroyCondition_generic((SDL_Condition *)cond);
+            cond = NULL;
+        }
+    }
+#endif
+
+    return (SDL_Condition *)cond;
+}
+
+// Destroy a condition variable
+void SDL_DestroyCondition_generic(SDL_Condition *_cond)
+{
+    SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
+    if (cond) {
+        if (cond->sem) {
+            SDL_DestroySemaphore(cond->sem);
+        }
+        if (cond->handshake_sem) {
+            SDL_DestroySemaphore(cond->handshake_sem);
+        }
+        if (cond->signal_sem) {
+            SDL_DestroySemaphore(cond->signal_sem);
+        }
+        SDL_free(cond);
+    }
+}
+
+// Restart one of the threads that are waiting on the condition variable
+void SDL_SignalCondition_generic(SDL_Condition *_cond)
+{
+    SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
+    if (!cond) {
+        return;
+    }
+
+#ifndef SDL_THREADS_DISABLED
+    /* If there are waiting threads not already signalled, then
+       signal the condition and wait for the thread to respond.
+     */
+    SDL_WaitSemaphore(cond->signal_sem);
+    if (cond->num_waiting > cond->num_signals) {
+        cond->num_signals++;
+        SDL_SignalSemaphore(cond->sem);
+        SDL_SignalSemaphore(cond->signal_sem);
+        SDL_WaitSemaphore(cond->handshake_sem);
+    } else {
+        SDL_SignalSemaphore(cond->signal_sem);
+    }
+#endif
+}
+
+// Restart all threads that are waiting on the condition variable
+void SDL_BroadcastCondition_generic(SDL_Condition *_cond)
+{
+    SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
+    if (!cond) {
+        return;
+    }
+
+#ifndef SDL_THREADS_DISABLED
+    /* If there are waiting threads not already signalled, then
+       signal the condition and wait for the thread to respond.
+     */
+    SDL_WaitSemaphore(cond->signal_sem);
+    if (cond->num_waiting > cond->num_signals) {
+        const int num_waiting = (cond->num_waiting - cond->num_signals);
+        cond->num_signals = cond->num_waiting;
+        for (int i = 0; i < num_waiting; i++) {
+            SDL_SignalSemaphore(cond->sem);
+        }
+        /* Now all released threads are blocked here, waiting for us.
+           Collect them all (and win fabulous prizes!) :-)
+         */
+        SDL_SignalSemaphore(cond->signal_sem);
+        for (int i = 0; i < num_waiting; i++) {
+            SDL_WaitSemaphore(cond->handshake_sem);
+        }
+    } else {
+        SDL_SignalSemaphore(cond->signal_sem);
+    }
+#endif
+}
+
+/* Wait on the condition variable for at most 'timeoutNS' nanoseconds.
+   The mutex must be locked before entering this function!
+   The mutex is unlocked during the wait, and locked again after the wait.
+
+Typical use:
+
+Thread A:
+    SDL_LockMutex(lock);
+    while ( ! condition ) {
+        SDL_WaitCondition(cond, lock);
+    }
+    SDL_UnlockMutex(lock);
+
+Thread B:
+    SDL_LockMutex(lock);
+    ...
+    condition = true;
+    ...
+    SDL_SignalCondition(cond);
+    SDL_UnlockMutex(lock);
+ */
+bool SDL_WaitConditionTimeoutNS_generic(SDL_Condition *_cond, SDL_Mutex *mutex, Sint64 timeoutNS)
+{
+    SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
+    bool result = true;
+
+    if (!cond || !mutex) {
+        return true;
+    }
+
+#ifndef SDL_THREADS_DISABLED
+    /* Obtain the protection mutex, and increment the number of waiters.
+       This allows the signal mechanism to only perform a signal if there
+       are waiting threads.
+     */
+    SDL_WaitSemaphore(cond->signal_sem);
+    cond->num_waiting++;
+    SDL_SignalSemaphore(cond->signal_sem);
+
+    // Unlock the mutex, as is required by condition variable semantics
+    SDL_UnlockMutex(mutex);
+
+    // Wait for a signal
+    result = SDL_WaitSemaphoreTimeoutNS(cond->sem, timeoutNS);
+
+    /* Let the signaler know we have completed the wait, otherwise
+       the signaler can race ahead and get the condition semaphore
+       if we are stopped between the mutex unlock and semaphore wait,
+       giving a deadlock.  See the following URL for details:
+       http://web.archive.org/web/20010914175514/http://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html#Workshop
+     */
+    SDL_WaitSemaphore(cond->signal_sem);
+    if (cond->num_signals > 0) {
+        SDL_SignalSemaphore(cond->handshake_sem);
+        cond->num_signals--;
+    }
+    cond->num_waiting--;
+    SDL_SignalSemaphore(cond->signal_sem);
+
+    // Lock the mutex, as is required by condition variable semantics
+    SDL_LockMutex(mutex);
+#endif
+
+    return result;
+}
+
+#ifndef SDL_THREAD_GENERIC_COND_SUFFIX
+bool SDL_WaitConditionTimeoutNS(SDL_Condition *cond, SDL_Mutex *mutex, Sint64 timeoutNS)
+{
+    return SDL_WaitConditionTimeoutNS_generic(cond, mutex, timeoutNS);
+}
+#endif