/*
 * Copyright (C) 2008 The Android Open Source Project
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *  * Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the 
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
 * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
 * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
#include <pthread.h>
#include <semaphore.h>
#include <errno.h>
#include <stdio.h>
#include <time.h>
#include <string.h>
#include <unistd.h>

/* a simple semaphore test, using three threads
 *
 *  a semaphore is initialized with a value of 1
 *
 *  Thread 1, 2 and 3 start at the same time
 *
 *  Thread 1 takes the semaphore, then sleeps for 2 seconds, then post the semaphore
 *  Thread 2 sleeps for 1 second, then waits the semaphore, sleeps for 2 seconds, then post the semaphoe
 *  Thread 3 sleeps 3 seconds, waits for the semaphore
 */

static  sem_t   semaphore;

static void*
_thread1( void* unused )
{
    printf( "thread 1: waiting for semaphore\n" );
    if ( sem_wait( &semaphore ) < 0 ) {
        printf( "thread 1: could not wait for semaphore: %s\n", strerror(errno) );
        return NULL;
    }
    printf( "thread 1: got the semaphore ! sleeping for 2 seconds\n" );
    sleep( 2 );
    printf( "thread 1: awake !! posting semaphore\n" );
    if ( sem_post( &semaphore ) < 0 ) {
        printf( "thread 2: could not post semaphore: %s\n", strerror(errno) );
    }
    printf( "thread 1: quitting\n" );
    return NULL;
}

static void*
_thread2( void* unused )
{
    printf( "thread 2: sleeping for 1 second\n" );
    sleep(1);
    printf( "thread 2: awake !! waiting for semaphore\n" );
    if ( sem_wait( &semaphore ) < 0 ) {
        printf( "thread 2: could not wait for semaphore: %s\n", strerror(errno) );
        return NULL;
    }
    printf( "thread 2: got the semaphore ! sleeping for 2 seconds\n" );
    sleep( 2 );
    printf( "thread 2: awake !! posting semaphore\n" );
    if ( sem_post( &semaphore ) < 0 ) {
        printf( "thread 2: could not post semaphore: %s\n", strerror(errno) );
    }
    printf( "thread 2: quitting\n" );
    return NULL;
}


static void*
_thread3( void* unused )
{
    printf( "thread 3: sleeping for 3 seconds\n" );
    sleep(3);
    printf( "thread 3: awake !! waiting for semaphore\n" );
    if ( sem_wait( &semaphore ) < 0 ) {
        printf( "thread 3: could not wait for semaphore: %s\n", strerror(errno) );
        return NULL;
    }
    printf( "thread 3: got semaphore. quitting\n" );
    return NULL;
}

typedef void*  (*thread_func)(void*);

static const  thread_func  thread_routines[] =
{
    &_thread1,
    &_thread2,
    &_thread3
};

int  main( void )
{
    pthread_t   t[3];
    int         nn;

    if ( sem_init( &semaphore, 0, 1 ) < 0 ) {
        printf( "could not initialize semaphore: %s\n", strerror(errno) );
        return -1;
    }

    for ( nn = 0; nn < 3; nn++ ) {
        if ( pthread_create( &t[nn], NULL, thread_routines[nn], NULL ) < 0 ) {
            printf("could not create thread %d: %s\n", nn+1, strerror(errno) );
            return -2;
        }
    }
    sleep( 5 );
    return 0;
}