waitpid(2) - perldoc - phpman

Che Dong

Wait for the termination of arbitrary processes.

Sleep until all processes whose PIDs have been specified have exited
waitpid {{pid1 pid2 ...}}
Sleep for at most `n` seconds
waitpid {{-t|--timeout}} {{n}} {{pid1 pid2 ...}}
Do not error if specified PIDs have already exited
waitpid {{-e|--exited}} {{pid1 pid2 ...}}
Sleep until `n` of the specified processes have exited
waitpid {{-c|--count}} {{n}} {{pid1 pid2 ...}}
Display help
waitpid {{-h|--help}}

    waitpid PID,FLAGS
            Waits for a particular child process to terminate and returns
            the pid of the deceased process, or -1 if there is no such child
            process. A non-blocking wait (with WNOHANG in FLAGS) can return
            0 if there are child processes matching PID but none have
            terminated yet. The status is returned in $? and
            "${^CHILD_ERROR_NATIVE}".

            A PID of 0 indicates to wait for any child process whose process
            group ID is equal to that of the current process. A PID of less
            than -1 indicates to wait for any child process whose process
            group ID is equal to -PID. A PID of -1 indicates to wait for any
            child process.

            If you say

                use POSIX ":sys_wait_h";

                my $kid;
                do {
                    $kid = waitpid(-1, WNOHANG);
                } while $kid > 0;

            or

                1 while waitpid(-1, WNOHANG) > 0;

            then you can do a non-blocking wait for all pending zombie
            processes (see "WAIT" in POSIX). Non-blocking wait is available
            on machines supporting either the waitpid(2) or wait4(2)
            syscalls. However, waiting for a particular pid with FLAGS of 0
            is implemented everywhere. (Perl emulates the system call by
            remembering the status values of processes that have exited but
            have not been harvested by the Perl script yet.)

            Note that on some systems, a return value of -1 could mean that
            child processes are being automatically reaped. See perlipc for
            details, and for other examples.

            Portability issues: "waitpid" in perlport.