#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <stdio.h>

int main()
{
        struct flock lock;
        int fd;

        fd = open("a",O_WRONLY);

        lock.l_type = F_WRLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = 0;
        lock.l_len = 1;
        lock.l_pid = 0;
        printf("%d\n",fcntl(fd, F_SETLKW, &lock));
        sleep(20);
        lock.l_type = F_UNLCK;
        lock.l_whence = SEEK_SET;
        lock.l_start = 0;
        lock.l_len = 1;
        lock.l_pid = 0;
        printf("%d\n",fcntl(fd, F_SETLKW, &lock));

        close(fd);

        return(0);
}