waitpid
- 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. On some systems, a value of 0
indicates that there are processes still running. The status is returned in $?.
If you say
use POSIX ":sys_wait_h";
#...
do {
$kid = waitpid(-1, WNOHANG);
} until $kid > 0;
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then you can do a non-blocking wait for all pending zombie processes. Non-blocking wait
is available on machines supporting either the waitpid(2) or wait4(2) system calls. 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.
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