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Date: Mon, 08 Dec 2003 07:59:00 -0000
From: Shantanu Gogate <sagogate@yahoo.com>
Subject: help: weird behaviour of sem_getvalue
To: pthreads-win32@sources.redhat.com
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X-SW-Source: 2003/txt/msg00143.txt.bz2

Hi,
I am using pthreads-win32 package( was using pthreads-win32-2003-05-10.exe and also tried the
latest 2003-09-18.exe) but facing a weird problem using sem_getvalue. I have replicated what I am
trying to do thru this snippet of code which you can test for yourself. Basically there is a
semaphore which is set to one before the threads are launched. one or more threads continuously
check the value of this semaphore to see if it has become zero and if it has, then the thread
exits. Interestingly if you comment out the pthread_exit line then you that the sem_getvalue
returns the value of semaphore as zero for a brief period of time and then starts reporting it as
one again !! if i compile the same code on a linux box this anomaly is not observed. Is this is a
bug in win32-pthreads ? Any help would be appreciated.

Shantanu Gogate.

the code:

<<<<
#include <pthread.h>
#include <semaphore.h>
#include <stdio.h>      
                        
static sem_t g_sem_ready,g_sem_queue;
                
void *consumer(void *args) {
        int count=0,value;
        while(1) {
                sem_getvalue(&g_sem_ready,&value);
                printf("consumer ready= %d\n",value);
                if(value <= 0 ) {
                        sem_getvalue(&g_sem_queue,&value);
                //      printf("consumer exiting, with %d pending\n");
                        pthread_exit(0);
                }       
                else {
                        sem_wait(&g_sem_queue);
                        count++;
                //      printf("consumed %d\n",count);
                }
        }               
}          

void *producer(void *args) {
        int value,count=0;
        while(1) {
                sem_getvalue(&g_sem_ready,&value);
                printf("producer ready= %d\n",value);
                if(value <= 0 ) {
                        printf("producer exiting\n");
                //      pthread_exit(0);
                }
                else {
                        count++;
                //      printf("produced %d\n",count);
                        sem_post(&g_sem_queue);
                        if(count > 200)
                                pthread_exit(0);
                }
        }
}
int main(int argc, char *argv[]) {
        pthread_t th1, th2;
        int status;

        sem_init(&g_sem_ready,0,0);
        sem_init(&g_sem_queue,0,0);

        sem_post(&g_sem_ready);
        pthread_create(&th1,NULL, consumer, NULL);
        pthread_create(&th2,NULL, producer, NULL);
        sleep(10);
        printf("going down baby\n");
        sem_wait(&g_sem_ready);
        pthread_join(th2,(void **)&status);
        pthread_join(th1,(void **)&status);
}



>>>>

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