view src/thread/dc/SDL_syscond.c @ 641:df178851293b

Date: 28 Jun 2003 22:42:52 +0100 From: Alan Swanson Subject: Re: [SDL] New XFree 4.3 Video Mode Patch I have a wee amendment that moves the qsort in set_best_resolution to only occur after failing to find an exact match only. This would make absolutely sure we get a user set mode. While I've never had any problems for my normal resolutions (1280x1024, 1024x768, 800x600 & 640,480) while closely examining the output from qsort I've noticed it doesn't seem to sort the modes fully. These is one definite wrong at 1152x768 and a few that just look wrong to me. From a program (attached) I made to examine this more easily. X has sorted its mode list using the same method as ours (plus frequency), and our user modes get inserted without any other movement. On the patch I've made I've also changed cmpmodes to sort on vertical resolution and then horizontal. Ie vertical is now most significant bit.
author Sam Lantinga <slouken@libsdl.org>
date Sat, 28 Jun 2003 21:52:26 +0000
parents dad72daf44b3
children b8d311d90021
line wrap: on
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/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002  Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Library General Public
    License as published by the Free Software Foundation; either
    version 2 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Library General Public License for more details.

    You should have received a copy of the GNU Library General Public
    License along with this library; if not, write to the Free
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

    Sam Lantinga
    slouken@libsdl.org
*/

#ifdef SAVE_RCSID
static char rcsid =
 "@(#) $Id$";
#endif

/* 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 <stdio.h>
#include <stdlib.h>

#include "SDL_error.h"
#include "SDL_thread.h"

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

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

	cond = (SDL_cond *) malloc(sizeof(SDL_cond));
	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(cond);
			cond = NULL;
		}
	} else {
		SDL_OutOfMemory();
	}
	return(cond);
}

/* Destroy a condition variable */
void SDL_DestroyCond(SDL_cond *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);
		}
		free(cond);
	}
}

/* Restart one of the threads that are waiting on the condition variable */
int SDL_CondSignal(SDL_cond *cond)
{
	if ( ! cond ) {
		SDL_SetError("Passed a NULL condition variable");
		return -1;
	}

	/* 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(SDL_cond *cond)
{
	if ( ! cond ) {
		SDL_SetError("Passed a NULL condition variable");
		return -1;
	}

	/* 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);
	}
	SDL_UnlockMutex(lock);

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

	if ( ! cond ) {
		SDL_SetError("Passed a NULL condition variable");
		return -1;
	}

	/* 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://www-classic.be.com/aboutbe/benewsletter/volume_III/Issue40.html
	*/
	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(SDL_cond *cond, SDL_mutex *mutex)
{
	return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
}