#include <pthread.h>
#include <stdio.h>
#include "errors.h"

/* Initialize 2 mutexes. */
pthread_mutex_t mutex1 = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t mutex2 = PTHREAD_MUTEX_INITIALIZER;

void *
locking_thread_a( void *arg )
{
        int status;
	printf( "locking_thread_a starting\n" );
        status = pthread_mutex_lock( &mutex1 );
        if ( status != 0 )
                err_abort( status, "lock 1" );
        printf( "a has lock 1\n" );
        sched_yield();
        printf( "a now trying to get lock 2\n" );
        status = pthread_mutex_lock( &mutex2 );
        printf( "a has lock 2\n" );
        if ( status != 0 )
                err_abort( status, "lock 2" );
        pthread_mutex_unlock( &mutex1 );
        pthread_mutex_unlock( &mutex2 );
	printf( "locking_thread_a finishing\n" );
	pthread_exit( NULL );
}

void *
locking_thread_b( void *arg )
{
        int status;
	printf( "locking_thread_b starting\n" );
        status = pthread_mutex_lock( &mutex2 );
        if ( status != 0 )
                err_abort( status, "lock 2" );
        printf( "b has lock 2\n" );
        sched_yield();
        printf( "b now trying to get lock 1\n" );
        status = pthread_mutex_lock( &mutex1 );
        if ( status != 0 )
                err_abort( status, "lock 1" );
        printf( "b has lock 1\n" );
        pthread_mutex_unlock( &mutex2 );
        pthread_mutex_unlock( &mutex1 );
	printf( "locking_thread_b finishing\n" );
	pthread_exit( NULL );
}

int
main( int argc, char *argv[] )
{
	pthread_t thread1, thread2;
	int status;
        printf( "Creating thread a\n" );
        status = pthread_create( &thread1, NULL, locking_thread_a, NULL );
        if ( status )
                err_abort( status, "locking_thread_a" );
        printf( "Creating thread b\n" );
        status = pthread_create( &thread2, NULL, locking_thread_b, NULL );
        if ( status )
                err_abort( status, "locking_thread_b" );
	pthread_exit( NULL );
}