Pramod Srinivasan wrote:
> 
> I am trying interprocess locking using
> pthread_mutex_lock but have not been able to get it
> work, here is the test program and the output, what is
> wrong in the program?
> 

There is no need to call fork() when using threads, as the whole idea
is to save the overhead of creating multiple 'heavyweight' processes.
Assuming you want thread 2 to block until it gets a lock on the mutex,
try the following code:

/* Tested on Linux as I don't have access to a NetBSD machine from
    my current location. If the pthread emulation package you are
    using is any good, then this should work for you. */

#include <stdio.h>
#include </usr/pkg/include/pthread.h>

static pthread_mutex_t global_mutex = PTHREAD_MUTEX_INITIALIZER;

static void *thread1(void *);
static void *thread2(void *);

int main(int argc, char *argv[]) {
     pthread_t p1, p2;

     if(pthread_create(&p1, NULL, thread1, NULL)) {
         fputs("Unable to create first thread\n", stderr);
         return 1;
     }

     if(pthread_create(&p2, NULL, thread2, NULL)) {
         fputs("Unable to create second thread\n", stderr);
         return 1;
     }

     pthread_join(p1, NULL);

     return 0;
}

void *thread1(void *data) {
     unsigned i;

     fputs("Thread 1\n", stderr);
     pthread_mutex_lock(&global_mutex);
     while(1) {
         fputs("Working in thread 1\n", stderr);
         for(i = 0; i < 10000000; i++);
     }

     return NULL;
}

void *thread2(void *data) {
     unsigned i;

     fputs("Thread 2\n", stderr);
     pthread_mutex_lock(&global_mutex);
     while(1) {
         fputs("**** Working in thread 2 ****\n", stderr);
         for(i = 0; i < 10000000; i++);
     }

     return NULL;
}

Chris

-- 
chris.wareham@iosystems.co.uk (work)
cwareham@btinternet.com (home)