From: Gary Wright <gwtmp01@...>
Date: 2007-03-01T08:14:42+09:00
Subject: Re: How to check if child process is still alive?


On Feb 28, 2007, at 5:17 PM, Andreas S wrote:

> how do you check if your child process from fork still alive or  
> not? In perl I can send kill(0, $cid), I think. But Process.kill(0,  
> child_id) always returns 1.
>
> To be honest, I couldn't get the perl code to work either. It  
> always returns 1 too.
>
> I can do `ps -p #{child_id}` but I wonder if Process.kill should  
> work too.

Using Process.kill(0, pid) will return 1 as long as the process  
exists. In
your situation, I'm guessing that the child process has terminated
but continues to exist as a zombie process.  You have to call  
Process.wait
to reap the child process in order for the child process to disappear  
entirely.

pid = fork { sleep(10) }

puts Process.kill(0, pid)        # 1
sleep 15
puts Process.kill(0, pid)        # 1, process is a zombie at this point
Process.wait
puts Process.kill(0, pid)        # exception, process doesn't exist

Gary Wright