struct flock {
             ...
             short l_type;    /* Type of lock: F_RDLCK,
                                 F_WRLCK, F_UNLCK */
             short l_whence;  /* How to interpret l_start:
                                 SEEK_SET, SEEK_CUR, SEEK_END */
             off_t l_start;   /* Starting offset for lock */
             off_t l_len;     /* Number of bytes to lock */
             pid_t l_pid;     /* PID of process blocking our lock
                                 (F_GETLK only) */
             ...
         };

##</code><code>##

fcntl(FILEHANDLE, F_SETLKW, pack("sslli", F_WRLCK, SEEK_SET, 0, 0, 0));

##</code><code>##

fcntl(FILEHANDLE, F_SETLKW, pack("s!s!l!l!i!", F_WRLCK, SEEK_SET, 0, 0, 0));