cond_usg.c

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

 #define NUM_THREADS 3
 #define TCOUNT 100
 #define COUNT_LIMIT 20

 int count = 10;
 pthread_mutex_t count_mutex ;
 pthread_cond_t count_threshold_cv ;

 void *inc_count (void * tid ){
 int i ;
 long my_id = (long) tid ;
 for ( i = 0 ; i < TCOUNT; i++){
 pthread_mutex_lock(&count_mutex ) ;
 count++;
 if ( count == COUNT_LIMIT){
printf( "inc_count ( ) : thread %ld , count = %d ,threshold reached . \n" , my_id, count ) ;
 pthread_cond_signal(&count_threshold_cv ) ;
 printf( "Just sent s i g n a l \n" ) ;
 }

 printf( "inc_count ( ) : thread %ld , count = %d ,unlocking mutex\n" , my_id, count ) ;
 pthread_mutex_unlock(&count_mutex ) ;
 sleep( 1 ) ;
 }
 pthread_exit (NULL) ;
 }

 void *watch_count(void * tid ){
 long my_id = (long) tid ;
 printf( " Starting watch_count ( ) : thread %ld \n" , my_id ) ;

 pthread_mutex_lock(&count_mutex ) ;
 while( count < COUNT_LIMIT){
printf( "watch_count ( ) : thread %ld , count = %d ,waiting . . . \n" , my_id, count ) ;
 pthread_cond_wait(&count_threshold_cv ,&count_mutex ) ;
 printf( "watch_count ( ) : thread %ld . Condition s i g n a l received .Count = %d\n" ,my_id, count) ;
 printf( "watch_count ( ) : thread %ld Updating the count value . . . \n" , my_id ) ;
 count += 80;
printf( "watch_count ( ) : thread %ld count now = %d\n" , my_id, count ) ;
 }
 printf( "watch_count ( ) : thread %ld . Unlocking mutex . \n" , my_id ) ;
 pthread_mutex_unlock(&count_mutex ) ;
 pthread_exit (NULL) ;
 }

 int main( int argc , char** argv )
 {
 int i , rc ;
 pthread_t p1 , p2 , p3 ;
 long t1 = 1 , t2 = 2 , t3 = 3 ;
 pthread_attr_t attr ;

 printf( "main : begin\n" ) ;
 pthread_mutex_init(&count_mutex , NULL) ;
 pthread_cond_init(&count_threshold_cv , NULL) ;

 pthread_attr_init(&attr) ;
 pthread_attr_setdetachstate(&attr , PTHREAD_CREATE_JOINABLE) ;

 pthread_create(&p1 , &attr , watch_count , (void*)t1 ) ;
 pthread_create(&p2 , &attr , inc_count , (void*) t2 ) ;
 pthread_create(&p3 , &attr , inc_count , (void*) t3 ) ;

 rc = pthread_join (p1 , NULL) ; assert ( rc == 0 ) ;
 rc = pthread_join (p2 , NULL) ; assert ( rc == 0 ) ;
 rc = pthread_join (p3 , NULL) ; assert ( rc == 0 ) ;

 printf( "main : finish,final count = %d\n" , count ) ;

 pthread_attr_destroy(&attr ) ;
 pthread_mutex_destroy(&count_mutex ) ;
 pthread_cond_destroy(&count_threshold_cv ) ;
 pthread_exit (NULL) ;

 return 0 ;
 }