freebsd stable - Sep 2005 - Problem About how to use shared posix semaphore

Hi,
    I always get the error message:"Operation not permitted" When I
use sem_init set pshared argument equal 1. Compiling as : "gcc -o sem_test
sem_test.c -lc_r". My freebsd ver is release 5.4 p6.
    Test code appear below:
      1 #include <sys/types.h>
      2 #include <string.h>
      3 #include <stdio.h>
      4 #include <sys/stat.h>
      5 #include <unistd.h>
      6 #include <fcntl.h>
      7 #include <errno.h>
      8 #include <pthread.h>
      9 #include <semaphore.h>
     10
     11 int main(int argc, char ** argv)
     12 {
     13     sem_t   mutex;
     14     if (-1 == sem_init (&mutex, 1, 1)) {
     15         printf("sem init error:%s\n", strerror(errno));
     16         exit(0);
     17     }
     18     sem_wait (&mutex);
     19     printf("sem wait ok:\n");
     20     sem_post (&mutex);
     21     sem_destroy (&mutex);
     22     return 0;
     23 }

Best regards,
Gary Li

On Thu, 2005-09-29 at 20:47 +0800, Gary Li-126 wrote:
> Hi,
>     I always get the error message:"Operation not permitted" When
I use sem_init set pshared argument equal 1. Compiling as : "gcc -o
sem_test sem_test.c -lc_r". My freebsd ver is release 5.4 p6.
>From sem_init(3):
A non-zero value for pshared specifies a
shared semaphore that can be used by multiple processes, which this
implementation is not capable of.

I suspect you're asking the impossible.  You could try using a different
threading library, but libc_r won't work:

/usr/src/lib/libc_r/uthread/uthread_sem.c:

_sem_init(sem_t *sem, int pshared, unsigned int value)
{
 [...]
        if (pshared != 0) {
                /*
                 * The user wants a semaphore that can be shared among
                 * processes, which this implementation can't do.  Sounds
like a
                 * permissions problem to me (yeah right).
                 */
                errno = EPERM;
                retval = -1;
                goto RETURN;
        }

This return code is documenbted in the sem_init man page:

[EPERM]            Unable to initialize a shared semaphore.

Gavin