Calls the System V IPC function semop to perform semaphore operations such as signalling and waiting. OPSTRING must be a packed array of semop structures. Each semop structure can be generated with pack("s!3", $semnum, $semop, $semflag) . The length of OPSTRING implies the number of semaphore operations. Returns true if successful, or false if there is an error. As an example, the following code waits on semaphore $semnum of semaphore id $semid:

    $semop = pack("s!3", $semnum, -1, 0);
    die "Semaphore trouble: $!\n" unless semop($semid, $semop);

To signal the semaphore, replace -1 with 1 . See also "SysV IPC" in perlipc, IPC::SysV , and IPC::SysV::Semaphore documentation.