Waits for a particular child process to terminate and returns the pid of
the deceased process, or
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
A PID of
indicates to wait for any child process whose process group ID is
equal to that of the current process. A PID of less than
wait for any child process whose process group ID is equal to -PID. A PID of
indicates to wait for any child process.
If you say
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
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
could mean that child
processes are being automatically reaped. See perlipc for details,
and for other examples.
Portability issues: waitpid in perlport.