Beefy Boxes and Bandwidth Generously Provided by pair Networks
No such thing as a small change

Re: Having a difficult time understanding fork()

by crashtest (Curate)
on Apr 07, 2010 at 02:19 UTC ( #833165=note: print w/replies, xml ) Need Help??

in reply to Having a difficult time understanding fork()

Based on the description of your requirement, it sounds like you will need to fork two children - one to check the server, one to do the countdown. Something like this:

use strict; use warnings; use feature qw(:5.10); # Fork off two child processes my ($who_am_i, $countdown_pid, $checking_pid); $countdown_pid = fork(); if ($countdown_pid == 0){ $who_am_i = "countdown process"; } elsif ($countdown_pid){ $checking_pid = fork(); if ($checking_pid == 0){ $who_am_i = "checking process"; } elsif ($checking_pid){ $who_am_i = "controlling process"; } else{ die "Error forking: $!"; } } else{ die "Error forking: $!"; } # Each process does different things: given($who_am_i){ when ("countdown process"){ sleep_count(3, 'Verifying with Nagios that resin is down: '); } when ("checking process"){ # repeatedly do server check via "nagios" } when ("controlling process"){ # Wait on the "checking process" to complete. waitpid($checking_pid, 0); # Kill countdown timer kill("TERM", $countdown_pid); waitpid($countdown_pid, 0); } }

You should probably check the exit status of your child processes (via $? after the waitpid calls).

Hope this helps.

Update: Actually, there's no need to have three processes. Two is enough, as in your post, although conceptually I like the idea of delegating each subtask to separate child processes.

Perhaps the only piece that was really missing from your code was killing off the countdown timer.

Log In?

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://833165]
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others taking refuge in the Monastery: (3)
As of 2020-06-07 09:29 GMT
Find Nodes?
    Voting Booth?
    Do you really want to know if there is extraterrestrial life?

    Results (42 votes). Check out past polls.