POSIX shm_unlink() problem

4 Nov 2004

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I'm attaching a fairly simple test case that works on FreeBSD and Linux.
Thanks,
jeff
% gcc -g tstshm.c
% ./a.out
shm_unlink(): Invalid argument

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <sys/wait.h>
#include <sys/stat.h>

main(){
    int     fd;
    pid_t   pid;

    /*
     * linux doesn't like sub-paths, and FreeBSD likes "real" directory
     * permissions for shared mem names...
     */
#ifdef linux
    char    memname[] = "/MEMNAME1";
#else
    char    memname[] = "/tmp/MEMNAME9";
#endif
    char    hipop[] = "Hello Parent Process";
    char    *tst;

    fd = shm_open(memname,O_RDWR|O_CREAT|O_EXCL,0666);
    if(fd < 0){
        perror("shm_open():");
        exit(1);
    }

    if(shm_unlink(memname) != 0){
        perror("shm_unlink()");
        exit(1);
    }

    pid = fork();

    if(pid < 0){
        perror("fork(): ");
        exit(1);
    }

    if(pid > 0){
        /*
         * parent
         */
        int wstatus=0;
        struct stat sbuf;

        /*
         * Wait for child to exit.
         */
WAIT_AGAIN:
        if(waitpid(pid,&wstatus,0) != pid){
            if(errno == EINTR)
                goto WAIT_AGAIN;
            perror("waitpid(): ");
            exit(1);
        }

        if(!WIFEXITED(wstatus) || WEXITSTATUS(wstatus)){
            perror("Child process exited in strange state.");
            exit(1);
        }

        /*
         * Determine size of the message child left behind.
         */
        if(fstat(fd,&sbuf) != 0){
            perror("fstat(): ");
            exit(1);
        }

        /*
         * Map the child message into 'tst'.
         */
        tst = mmap(NULL,sbuf.st_size,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
        if(tst == MAP_FAILED){
            perror("Parent:mmap(): ");
            exit(1);
        }

        fprintf(stdout,"Parent read \"%s\"\n",tst);
        exit(0);
    }

    /*
     * child
     */

    /*
     * Set the size of the shm segment.
     */
    if(ftruncate(fd,sizeof(hipop)) != 0){
        perror("ftruncate(): ");
        exit(1);
    }

    /*
     * Map it as a char *
     */
    tst = mmap(NULL,sizeof(hipop),PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
    if(tst == MAP_FAILED){
        perror("child:mmap(): ");
        exit(1);
    }

    /*
     * Leave a message in the shm for the parent process to read after
     * exit.
     */
    strcpy(tst,hipop);

    exit(0);
}

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I am having problems using shm_unlink() on Panther. Is anyone using this
system call successfully on OS X?
After failure, errno is set to EINVAL (which is not even one of the
documented possible errors).

POSIX shm_unlink() problem

Jeff W. Boote