fcntl file locking test

main.c

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

int var_glb; /* A global variable*/

int main(int argc, char **argv){
    struct flock fl;
    fl.l_type = F_WRLCK;
    fl.l_whence = SEEK_SET;
    fl.l_start = 0;
    fl.l_len = 0;
    fl.l_pid = getpid();
    FILE *fp;
    int fd;

    fp = fopen("/tmp/test.dest", "a+");
    fd = fileno(fp);

    printf("opened by %d. About to lock.\n", getpid());

    if (fcntl(fd, F_SETLKW, &fl) < 0){
        printf("fcntl twidgie failed \n");
    }
    else{
        printf("Locked by %d\n", getpid());
    }

    fprintf(fp, "These are the times that try men's soils.\n");
    fprintf(fp, "Why do the barnicles seeth in the deep?\n");
    fprintf(fp, "Maybe the stolid twidgies lurk until this day?\n\n\n");

    printf("%d is going to sleep\n", getpid());
    sleep(10);

    fl.l_type = F_UNLCK;
    if (fcntl(fd, F_SETLK, &fl) < 0){
        printf("fcntl (unlock) twidgie failed\n");
    }
    else{
        printf("UnLocked by %d\n", getpid());
    }

    fclose(fp);
    exit(0);
}