/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2006 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

#include "SDL_thread.h"
#include "SDL_timer.h"


#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
#include <errno.h>

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


struct SDL_semaphore {
	int id;
};

/* Not defined by many operating systems, use configure to detect */
/*
#if !defined(HAVE_SEMUN)
union semun {
	int val;
	struct semid_ds *buf;
	ushort *array;
};
#endif
*/

static struct sembuf op_trywait[2] = {
	{ 0, -1, (IPC_NOWAIT|SEM_UNDO) } /* Decrement semaphore, no block */
};
static struct sembuf op_wait[2] = {
	{ 0, -1, SEM_UNDO }		/* Decrement semaphore */
};
static struct sembuf op_post[1] = {
	{ 0, 1, (IPC_NOWAIT|SEM_UNDO) }	/* Increment semaphore */
};

/* Create a blockable semaphore */
SDL_sem *SDL_CreateSemaphore(Uint32 initial_value)
{
	extern int _creating_thread_lock;	/* SDL_threads.c */
	SDL_sem *sem;
	union semun init;
	key_t key;

	sem = (SDL_sem *)SDL_malloc(sizeof(*sem));
	if ( sem == NULL ) {
		SDL_OutOfMemory();
		return(NULL);
	}
	/* This flag is true if we are creating the thread manager sem,
	   which is never freed.  This allows us to reuse the same sem.
	*/
	if ( _creating_thread_lock ) {
		key = 'S'+'D'+'L';
	} else {
		key = IPC_PRIVATE;
	}
	/* Keep trying to create sem while we don't own the requested key */
	do {
		if ( key != IPC_PRIVATE ) {
			++key;
		}
		sem->id = semget(key, 1, (0600|IPC_CREAT));
	} while ((sem->id < 0) && (key != IPC_PRIVATE) && (errno == EACCES));

	/* Report the error if we eventually failed */
	if ( sem->id < 0 ) {
		SDL_SetError("Couldn't create semaphore");
		SDL_free(sem);
		return(NULL);
	}
	init.val = initial_value;	/* Initialize semaphore */
	semctl(sem->id, 0, SETVAL, init);
	return(sem);
}

void SDL_DestroySemaphore(SDL_sem *sem)
{
	if ( sem ) {
#ifdef __IRIX__
		semctl(sem->id, 0, IPC_RMID);
#else
		union semun dummy;
		dummy.val = 0;
		semctl(sem->id, 0, IPC_RMID, dummy);
#endif
		SDL_free(sem);
	}
}

int SDL_SemTryWait(SDL_sem *sem)
{
	int retval;

	if ( ! sem ) {
		SDL_SetError("Passed a NULL semaphore");
		return -1;
	}

	retval = 0;
  tryagain:
	if ( semop(sem->id, op_trywait, 1) < 0 ) {
		if ( errno == EINTR ) {
			goto tryagain;
		}
		retval = SDL_MUTEX_TIMEDOUT;
	}
	return retval;
}

int SDL_SemWait(SDL_sem *sem)
{
	int retval;

	if ( ! sem ) {
		SDL_SetError("Passed a NULL semaphore");
		return -1;
	}

	retval = 0;
  tryagain:
	if ( semop(sem->id, op_wait, 1) < 0 ) {
		if ( errno == EINTR ) {
			goto tryagain;
		}
		SDL_SetError("Semaphore operation error");
		retval = -1;
	}
	return retval;
}

int SDL_SemWaitTimeout(SDL_sem *sem, Uint32 timeout)
{
	int retval;

	if ( ! sem ) {
		SDL_SetError("Passed a NULL semaphore");
		return -1;
	}

	/* Try the easy cases first */
	if ( timeout == 0 ) {
		return SDL_SemTryWait(sem);
	}
	if ( timeout == SDL_MUTEX_MAXWAIT ) {
		return SDL_SemWait(sem);
	}

	/* Ack!  We have to busy wait... */
	timeout += SDL_GetTicks();
	do {
		retval = SDL_SemTryWait(sem);
		if ( retval == 0 ) {
			break;
		}
		SDL_Delay(1);
	} while ( SDL_GetTicks() < timeout );

	return retval;
}

Uint32 SDL_SemValue(SDL_sem *sem)
{
	int semval;
	Uint32 value;
	
	value = 0;
	if ( sem ) {
	  tryagain:
#ifdef __IRIX__
		semval = semctl(sem->id, 0, GETVAL);
#else
		{
		union semun arg;
		arg.val = 0;
		semval = semctl(sem->id, 0, GETVAL, arg);
		}
#endif
		if ( semval < 0 ) {
			if ( errno == EINTR ) {
				goto tryagain;
			}
		} else {
			value = (Uint32)semval;
		}
	}
	return value;
}

int SDL_SemPost(SDL_sem *sem)
{
	int retval;

	if ( ! sem ) {
		SDL_SetError("Passed a NULL semaphore");
		return -1;
	}

	retval = 0;
  tryagain:
	if ( semop(sem->id, op_post, 1) < 0 ) {
		if ( errno == EINTR ) {
			goto tryagain;
		}
		SDL_SetError("Semaphore operation error");
		retval = -1;
	}
	return retval;
}
