From: Morton Goldberg <m_goldberg@...>
Date: 2006-11-21T13:38:17+09:00
Subject: Re: fork, trap and exec. Pickaxe typo?

On Nov 20, 2006, at 4:25 PM, Nate Murray wrote:

> This is so strange. I feel that I am really missing something here.
>
> Here is my updated code, but the output is odd:
>
> require 'pp'
>
> trap("CLD") {
>   pid = Process.wait

I think this causes a conflict with Process.waitall below. I don't  
understand why you're doing this and a waitall. One thing seems  
clear: any child process whose exit is caught here won't be caught by  
the waitall below.

>   puts "Child pid #{pid}: terminated"
> }
>
> 1.upto(4) do
>   fork do
>     exec("sleep 3 && echo \"hello $HOSTNAME #{Process.pid}\n\"")
>   end
> end
>
> pp Process.waitall

The following code and output may give you some ideas about what is  
happening.

<code>
DEBUG = []

trap("CLD") {
    pid = Process.wait
    DEBUG << "Child pid #{pid} terminated"
}

begin
    4.times do
       if fork.nil?
          exec(%{echo "hello from child #{Process.pid}"})
       else
          sleep 1
       end
    end
ensure
    DEBUG.each { |s| puts s }
end
</code>

<results>
RubyMate r5712 running Ruby v1.8.2 (/usr/bin/ruby)
hello from child 1743
hello from child 1744
hello from child 1745
hello from child 1746
Child pid 1743 terminated
Child pid 1744 terminated
Child pid 1745 terminated
Child pid 1746 terminated
</results>

Regards, Morton