src/thread/generic/SDL_syscond.c - third_party/sdl - Git at Google

 /*
   Simple DirectMedia Layer
   Copyright (C) 1997-2021 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 "SDL_thread.h"

 #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
  */
 #if !SDL_THREAD_GENERIC_COND_SUFFIX
 #define SDL_CreateCond_generic      SDL_CreateCond
 #define SDL_DestroyCond_generic     SDL_DestroyCond
 #define SDL_CondSignal_generic      SDL_CondSignal
 #define SDL_CondBroadcast_generic   SDL_CondBroadcast
 #define SDL_CondWait_generic        SDL_CondWait
 #define SDL_CondWaitTimeout_generic SDL_CondWaitTimeout
 #endif

 typedef struct SDL_cond_generic
 {
     SDL_mutex *lock;
     int waiting;
     int signals;
     SDL_sem *wait_sem;
     SDL_sem *wait_done;
 } SDL_cond_generic;

 /* Create a condition variable */
 SDL_cond *
 SDL_CreateCond_generic(void)
 {
     SDL_cond_generic *cond;

     cond = (SDL_cond_generic *) SDL_malloc(sizeof(SDL_cond_generic));
     if (cond) {
         cond->lock = SDL_CreateMutex();
         cond->wait_sem = SDL_CreateSemaphore(0);
         cond->wait_done = SDL_CreateSemaphore(0);
         cond->waiting = cond->signals = 0;
         if (!cond->lock || !cond->wait_sem || !cond->wait_done) {
             SDL_DestroyCond_generic((SDL_cond *)cond);
             cond = NULL;
         }
     } else {
         SDL_OutOfMemory();
     }
     return (SDL_cond *)cond;
 }

 /* Destroy a condition variable */
 void
 SDL_DestroyCond_generic(SDL_cond * _cond)
 {
     SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
     if (cond) {
         if (cond->wait_sem) {
             SDL_DestroySemaphore(cond->wait_sem);
         }
         if (cond->wait_done) {
             SDL_DestroySemaphore(cond->wait_done);
         }
         if (cond->lock) {
             SDL_DestroyMutex(cond->lock);
         }
         SDL_free(cond);
     }
 }

 /* Restart one of the threads that are waiting on the condition variable */
 int
 SDL_CondSignal_generic(SDL_cond * _cond)
 {
     SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
     if (!cond) {
         return SDL_SetError("Passed a NULL condition variable");
     }

     /* If there are waiting threads not already signalled, then
        signal the condition and wait for the thread to respond.
      */
     SDL_LockMutex(cond->lock);
     if (cond->waiting > cond->signals) {
         ++cond->signals;
         SDL_SemPost(cond->wait_sem);
         SDL_UnlockMutex(cond->lock);
         SDL_SemWait(cond->wait_done);
     } else {
         SDL_UnlockMutex(cond->lock);
     }

     return 0;
 }

 /* Restart all threads that are waiting on the condition variable */
 int
 SDL_CondBroadcast_generic(SDL_cond * _cond)
 {
     SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
     if (!cond) {
         return SDL_SetError("Passed a NULL condition variable");
     }

     /* If there are waiting threads not already signalled, then
        signal the condition and wait for the thread to respond.
      */
     SDL_LockMutex(cond->lock);
     if (cond->waiting > cond->signals) {
         int i, num_waiting;

         num_waiting = (cond->waiting - cond->signals);
         cond->signals = cond->waiting;
         for (i = 0; i < num_waiting; ++i) {
             SDL_SemPost(cond->wait_sem);
         }
         /* Now all released threads are blocked here, waiting for us.
            Collect them all (and win fabulous prizes!) :-)
          */
         SDL_UnlockMutex(cond->lock);
         for (i = 0; i < num_waiting; ++i) {
             SDL_SemWait(cond->wait_done);
         }
     } else {
         SDL_UnlockMutex(cond->lock);
     }

     return 0;
 }

 /* Wait on the condition variable for at most 'ms' milliseconds.
    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_CondWait(cond, lock);
     }
     SDL_UnlockMutex(lock);

 Thread B:
     SDL_LockMutex(lock);
     ...
     condition = true;
     ...
     SDL_CondSignal(cond);
     SDL_UnlockMutex(lock);
  */
 int
 SDL_CondWaitTimeout_generic(SDL_cond * _cond, SDL_mutex * mutex, Uint32 ms)
 {
     SDL_cond_generic *cond = (SDL_cond_generic *)_cond;
     int retval;

     if (!cond) {
         return SDL_SetError("Passed a NULL condition variable");
     }

     /* 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_LockMutex(cond->lock);
     ++cond->waiting;
     SDL_UnlockMutex(cond->lock);

     /* Unlock the mutex, as is required by condition variable semantics */
     SDL_UnlockMutex(mutex);

     /* Wait for a signal */
     if (ms == SDL_MUTEX_MAXWAIT) {
         retval = SDL_SemWait(cond->wait_sem);
     } else {
         retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
     }

     /* 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_LockMutex(cond->lock);
     if (cond->signals > 0) {
         /* If we timed out, we need to eat a condition signal */
         if (retval > 0) {
             SDL_SemWait(cond->wait_sem);
         }
         /* We always notify the signal thread that we are done */
         SDL_SemPost(cond->wait_done);

         /* Signal handshake complete */
         --cond->signals;
     }
     --cond->waiting;
     SDL_UnlockMutex(cond->lock);

     /* Lock the mutex, as is required by condition variable semantics */
     SDL_LockMutex(mutex);

     return retval;
 }

 /* Wait on the condition variable forever */
 int
 SDL_CondWait_generic(SDL_cond * cond, SDL_mutex * mutex)
 {
     return SDL_CondWaitTimeout_generic(cond, mutex, SDL_MUTEX_MAXWAIT);
 }

 /* vi: set ts=4 sw=4 expandtab: */
	/*
	Simple DirectMedia Layer
	Copyright (C) 1997-2021 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 "SDL_thread.h"

	#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
	*/
	#if !SDL_THREAD_GENERIC_COND_SUFFIX
	#define SDL_CreateCond_generic SDL_CreateCond
	#define SDL_DestroyCond_generic SDL_DestroyCond
	#define SDL_CondSignal_generic SDL_CondSignal
	#define SDL_CondBroadcast_generic SDL_CondBroadcast
	#define SDL_CondWait_generic SDL_CondWait
	#define SDL_CondWaitTimeout_generic SDL_CondWaitTimeout
	#endif

	typedef struct SDL_cond_generic
	{
	SDL_mutex *lock;
	int waiting;
	int signals;
	SDL_sem *wait_sem;
	SDL_sem *wait_done;
	} SDL_cond_generic;

	/* Create a condition variable */
	SDL_cond *
	SDL_CreateCond_generic(void)
	{
	SDL_cond_generic *cond;

	cond = (SDL_cond_generic *) SDL_malloc(sizeof(SDL_cond_generic));
	if (cond) {
	cond->lock = SDL_CreateMutex();
	cond->wait_sem = SDL_CreateSemaphore(0);
	cond->wait_done = SDL_CreateSemaphore(0);
	cond->waiting = cond->signals = 0;
	if (!cond->lock \|\| !cond->wait_sem \|\| !cond->wait_done) {
	SDL_DestroyCond_generic((SDL_cond *)cond);
	cond = NULL;
	}
	} else {
	SDL_OutOfMemory();
	}
	return (SDL_cond *)cond;
	}

	/* Destroy a condition variable */
	void
	SDL_DestroyCond_generic(SDL_cond * _cond)
	{
	SDL_cond_generic cond = (SDL_cond_generic )_cond;
	if (cond) {
	if (cond->wait_sem) {
	SDL_DestroySemaphore(cond->wait_sem);
	}
	if (cond->wait_done) {
	SDL_DestroySemaphore(cond->wait_done);
	}
	if (cond->lock) {
	SDL_DestroyMutex(cond->lock);
	}
	SDL_free(cond);
	}
	}

	/* Restart one of the threads that are waiting on the condition variable */
	int
	SDL_CondSignal_generic(SDL_cond * _cond)
	{
	SDL_cond_generic cond = (SDL_cond_generic )_cond;
	if (!cond) {
	return SDL_SetError("Passed a NULL condition variable");
	}

	/* If there are waiting threads not already signalled, then
	signal the condition and wait for the thread to respond.
	*/
	SDL_LockMutex(cond->lock);
	if (cond->waiting > cond->signals) {
	++cond->signals;
	SDL_SemPost(cond->wait_sem);
	SDL_UnlockMutex(cond->lock);
	SDL_SemWait(cond->wait_done);
	} else {
	SDL_UnlockMutex(cond->lock);
	}

	return 0;
	}

	/* Restart all threads that are waiting on the condition variable */
	int
	SDL_CondBroadcast_generic(SDL_cond * _cond)
	{
	SDL_cond_generic cond = (SDL_cond_generic )_cond;
	if (!cond) {
	return SDL_SetError("Passed a NULL condition variable");
	}

	/* If there are waiting threads not already signalled, then
	signal the condition and wait for the thread to respond.
	*/
	SDL_LockMutex(cond->lock);
	if (cond->waiting > cond->signals) {
	int i, num_waiting;

	num_waiting = (cond->waiting - cond->signals);
	cond->signals = cond->waiting;
	for (i = 0; i < num_waiting; ++i) {
	SDL_SemPost(cond->wait_sem);
	}
	/* Now all released threads are blocked here, waiting for us.
	Collect them all (and win fabulous prizes!) :-)
	*/
	SDL_UnlockMutex(cond->lock);
	for (i = 0; i < num_waiting; ++i) {
	SDL_SemWait(cond->wait_done);
	}
	} else {
	SDL_UnlockMutex(cond->lock);
	}

	return 0;
	}

	/* Wait on the condition variable for at most 'ms' milliseconds.
	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_CondWait(cond, lock);
	}
	SDL_UnlockMutex(lock);

	Thread B:
	SDL_LockMutex(lock);
	...
	condition = true;
	...
	SDL_CondSignal(cond);
	SDL_UnlockMutex(lock);
	*/
	int
	SDL_CondWaitTimeout_generic(SDL_cond * _cond, SDL_mutex * mutex, Uint32 ms)
	{
	SDL_cond_generic cond = (SDL_cond_generic )_cond;
	int retval;

	if (!cond) {
	return SDL_SetError("Passed a NULL condition variable");
	}

	/* 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_LockMutex(cond->lock);
	++cond->waiting;
	SDL_UnlockMutex(cond->lock);

	/* Unlock the mutex, as is required by condition variable semantics */
	SDL_UnlockMutex(mutex);

	/* Wait for a signal */
	if (ms == SDL_MUTEX_MAXWAIT) {
	retval = SDL_SemWait(cond->wait_sem);
	} else {
	retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
	}

	/* 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_LockMutex(cond->lock);
	if (cond->signals > 0) {
	/* If we timed out, we need to eat a condition signal */
	if (retval > 0) {
	SDL_SemWait(cond->wait_sem);
	}
	/* We always notify the signal thread that we are done */
	SDL_SemPost(cond->wait_done);

	/* Signal handshake complete */
	--cond->signals;
	}
	--cond->waiting;
	SDL_UnlockMutex(cond->lock);

	/* Lock the mutex, as is required by condition variable semantics */
	SDL_LockMutex(mutex);

	return retval;
	}

	/* Wait on the condition variable forever */
	int
	SDL_CondWait_generic(SDL_cond * cond, SDL_mutex * mutex)
	{
	return SDL_CondWaitTimeout_generic(cond, mutex, SDL_MUTEX_MAXWAIT);
	}

	/* vi: set ts=4 sw=4 expandtab: */