Feng,

Which version of netbsd do you use? I remeber vaguely that ipl did not
work for me as I was using an older version of netbsd. I think I was using
a 1.4.2 netbsd, but when I tried the same on 1.5.x, it worked fine.

--pramod



On Sat, 26 Oct 2002, Feng Lu wrote:

> Date: Sat, 26 Oct 2002 16:24:57 +1300 (NZDT)
> From: Feng Lu <Feng.Lu@mcs.vuw.ac.nz>
> To: netbsd-help@netbsd.org
> Subject: inter process locking
>
> Hi,
>
> I am using mutex for inter process locking. In the following code, I
> expect that when a process is runing, its another instance should wait
> until the previous instance completes. However, this does not work. why?
>
> code
> -----
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/types.h>
> #include <sys/ipc.h>
> #include <sys/shm.h>
> #include </usr/pkg/include/pthread.h>
>
> typedef struct {
>   pthread_mutex_t Interprocess_mutex;
>   int state;
> }share_t;
> share_t *share;
>
> void readline(FILE *fp);
>
> int main(int argc, char *args[]) {
>   pthread_mutexattr_t mattr;
>   int read_byte, i;
>   int shmid;
>   key_t key = 5347;
>   char *shm, *s;
>
>   //create a share memory
>   if((shmid = shmget(key, sizeof(share_t), IPC_CREAT|0666)) < 0) {
>     perror("shmget");
>     exit(1);
>   }
>
>   if((shm = shmat(shmid, NULL, 0)) == (char *)-1) {
>     perror("shamt");
>     exit(1);
>   }
>
>   share = (share_t *)shm;
>
>   if(share->state != 1 ) {
>     printf("init mutex\n");
>     share->state = 1;
>     pthread_mutexattr_init(&mattr);
>     pthread_mutexattr_setpshared(&mattr, PTHREAD_PROCESS_SHARED);
>     pthread_mutex_init(&share->Interprocess_mutex, &mattr);
>   }
>
>   printf("state = %d\n", share->state);
>
>   pthread_mutex_lock(&share->Interprocess_mutex);
>
>   for(i = 0; i < 200000; i++) {
>     printf("%d\n", i);
>   }
>
>   pthread_mutex_unlock(&share->Interprocess_mutex);
>   shmdt((const void *)share);
>
>   exit(0);
>
> }
>
>

----------------------------------------------------------------------
			Pramod Srinivasan,
			Software Engineer, Redback Networks
			350 Holger way,San Jose, CA 95134-1362
			PH - 408-750-8537 (O) 408-988-8475 (H)
-----------------------------------------------------------------------