/*
% cc -Xa -v -o priority.c -o prtest  -lpthread -lposix4
 
The main rotuine of this program creates 3 instances of 
"tester" threads. Each of these are given different priorities.
Higher number means higher priority.
All these three theads wait at a semaphore called "stop" whose initial
value is 0.

The main routine signals the "stop" semaphore 3 times.
The highest priority waiting thread is resumed first. 

This program shows how to set or get the priority of a thread
*/


#include <pthread.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <semaphore.h>

#define HIGH  30
#define MID   20
#define LOW   10

pthread_mutex_t	prt_lock	= PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t	prt_cv		= PTHREAD_COND_INITIALIZER;
int		prt		= 0;
sem_t   stop;


/* high priority thread 	*/

void * tester ( void *arg ) {
pthread_t myid;
int my_pr;
int policy;
struct sched_param prm;

    myid = pthread_self();
    pthread_getschedparam(myid, &policy,  &prm);
    my_pr = prm.sched_priority;
	printf( "Tester Thread %d  of priority %d waiting at stop\n", myid, my_pr );
    sem_wait( &stop );
	printf( "Tester Thread %d  of priority %d resumed from stop\n", myid, my_pr );
}


/* main - start here.					*/

main( int argc, char *argv[] ) {
	int		i;
	int		n;
	pthread_attr_t	attr;
	pthread_t	tid;
    struct sched_param param;

	printf( "Main started\n" );

    /* Initialize the value of the semaphore to 0 (third arg)  */
    sem_init( &stop,  0,  0);

	pthread_attr_init( &attr );

    param.sched_priority = MID;
	pthread_attr_setschedparam( &attr, &param);
    pthread_attr_setschedpolicy( &attr, SCHED_FIFO);


	if ( n = pthread_create( &tid, &attr, tester, NULL ) ) {
		fprintf( stderr, "pthread_create: %s\n", strerror( n ) );
		exit( 1 );
	}

    param.sched_priority = MID;
	pthread_attr_setschedparam( &attr, &param);
	if ( n = pthread_create( &tid, &attr, tester, NULL ) ) {
		fprintf( stderr, "pthread_create: %s\n", strerror( n ) );
		exit( 1 );
	}

    param.sched_priority = MID;
	pthread_attr_setschedparam( &attr, &param);
	if ( n = pthread_create( &tid, &attr, tester, NULL ) ) {
		fprintf( stderr, "pthread_create: %s\n", strerror( n ) );
		exit( 1 );
	}

	pthread_attr_destroy( &attr );

    sem_post( &stop );

    pthread_join(tid,  NULL);
	printf( "Main returned \n" );

	return( 0 );
}