/*! Simple semaphore example with sem_wait/sem_post interface */

#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <semaphore.h>

/*--- macro that simplifies handling errors with function calls ------------- */
#define ACT_WARN	0
#define ACT_STOP	1
#define CALL(ACT,FUNC,...)                                \
do {                                                      \
    if ( FUNC ( __VA_ARGS__ ) ) {                         \
        perror ( #FUNC );                                 \
        if ( ACT == ACT_STOP )                            \
            exit (1);                                     \
    }                                                     \
} while(0)

/* for example, instead of:
 *    if ( pthread_create ( &t1, NULL, worker, (void *) p ) ) {
 *        perror ( "pthread_create" );
 *        exit ( -1 );
 *    }
 * use:
 *    CALL ( ACT_STOP, pthread_create, &t1, NULL, worker, (void *) 1 );
 *
 *--------------------------------------------------------------------------- */

#define THREADS  6
static sem_t sem;
static int work_in_progress = 1;

static void *worker ( void *p )
{
	long id = (long) p;
	struct timespec t = { id, 0 };

	printf ( "Thread %ld starting\n", id );

	while ( work_in_progress ) {
		CALL ( ACT_STOP, sem_wait, &sem );

		printf ( "Thread %ld inside C.S.\n", id );

		CALL ( ACT_WARN, nanosleep, &t, NULL );

		printf("Thread %ld leaving C.S.\n", id);

		CALL ( ACT_STOP, sem_post, &sem );

		CALL ( ACT_WARN, nanosleep, &t, NULL );
	}

	printf ( "Thread %ld exiting\n", id );

	return NULL;
}

int main ()
{
	long i;
	pthread_t thr[THREADS];
	struct timespec t = { 50, 0 };

	CALL ( ACT_STOP, sem_init, &sem, 0, 1 );

	for ( i = 0; i < THREADS; i++ )
		CALL ( ACT_STOP, pthread_create, &thr[i], NULL, worker, (void *) i+1 );

	CALL ( ACT_WARN, nanosleep, &t, NULL );

	work_in_progress = 0;

	for ( i = 0; i < THREADS; i++ )
		CALL ( ACT_WARN, pthread_join, thr[i], NULL );

	return 0;
}

/* Example run:
$ gcc sem_wait.c -pthread -Wall
$ ./a.out
Thread 6 starting
Thread 6 inside C.S.
Thread 5 starting
Thread 4 starting
Thread 3 starting
Thread 2 starting
Thread 1 starting
Thread 6 leaving C.S.
Thread 5 inside C.S.
...
*/