Hi,

Thanks for the reply...Sorry I was not clear in my
previous email...

I was experimenting in inter process locking, reading
through the pthreads book I see that we can use
pthread_mutex_lock across processes if we have the
mutex in memory shared across processes, it appears to
me that NetBSD 1.5.1_ALPHA does have the pthread
library which supports mutex to be shared across
processes. In the code below, I expected that one of
the processes should have blocked on the mutex, but
the output show that both are running...not able to
understand why?

code
----
#include <stdio.h>
#include <fcntl.h>
#include <sys/mman.h>
#include </usr/pkg/include/pthread.h>

pthread_mutex_t *mutex;
pthread_mutexattr_t mattr;

void process1() {
   int i;

   printf("process 1\n");
   pthread_mutex_lock(mutex);
   for (;;) {

       printf("Working in process 1\n");
       for (i=0; i<10000000; i++);
   }

}

void process2() {
   int i;

   printf("process 2\n");
   pthread_mutex_lock(mutex);
   for (;;) {

       printf("****Working in process 2****\n");
       for (i=0; i<10000000; i++);
   }

}

main() {
    int fd;

    fd = open("/dev/zero", O_RDWR);
    mutex = (pthread_mutex_t *)mmap(NULL,
sizeof(pthread_mutex_t),
        PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);

    pthread_mutexattr_init(&mattr);
    pthread_mutexattr_setpshared(&mattr,
        PTHREAD_PROCESS_SHARED);

    pthread_mutex_init(mutex, &mattr);

    if (fork() == 0)
        process1();
    else
        process2();
}

output
-----
process 1
process 2
****Working in process 2****
Working in process 1
Working in process 1
****Working in process 2****
****Working in process 2****
Working in process 1
****Working in process 2****
****Working in process 2****
Working in process 1
****Working in process 2****
Working in process 1
****Working in process 2****
Working in process 1
****Working in process 2****
****Working in process 2****
****Working in process 2****
Working in process 1
****Working in process 2****
Working in process 1
****Working in process 2****
^C


--- Chris Wareham <chris.wareham@iosystems.co.uk>
wrote:
> 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)
> 


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