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

char data[] = "Lorem ipsum dolor sit amet";

int main( int argc, char *argv[] ) {

    char fname[] = "fcntl.test.XXXXXX";
    int fd = mkstemp(fname);
    write(fd, data, sizeof(data));

    struct flock lock;
    lock.l_type = F_RDLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 1;
    lock.l_pid = getpid();


    struct flock unlock;
    unlock.l_type = F_UNLCK;
    unlock.l_whence = SEEK_SET;
    unlock.l_start = 0;
    unlock.l_len = 1;
    unlock.l_pid = getpid();

    int c = 0;
    while (c++ < 100000000) {

        errno = 0;
        int res = fcntl(fd, F_SETLK, &lock);
        if (res < 0) {
            printf("F_SETLK F_RDLCK res = %d (%s)\n",
                res, strerror(errno));
            break;
        }
        
        errno = 0;
        res = fcntl(fd, F_SETLK, &unlock);
        if (res < 0) {
            printf("F_SETLK F_UNLCK res = %d (%s)\n",
                res, strerror(errno));
            break;
        }

    }

    printf("Successful cycles: %d\n", c - 1);
    close(fd);
    unlink(fname);

}