From: Nate Murray <jashmenn@...>
Date: 2006-11-21T06:25:11+09:00
Subject: Re: fork, trap and exec. Pickaxe typo?

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
  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

== output:

hello nate.cpo 4655

Child pid 4655: terminated
hello nate.cpo 4660

hello nate.cpo 4657

hello nate.cpo 4659

Child pid 4660: terminated
[[4659, #<Process::Status: pid=4659,exited(0)>],
 [4657, #<Process::Status: pid=4657,exited(0)>]]


The processes that are trapped call the callback and never end up in
Process.waitall. And those in Process.waitall never send the SIGCLD.

I think I need to do more research on this...

Hugh Sasse wrote:
> On Tue, 21 Nov 2006, Nate Murray wrote:
>
> > Yeah, but how do I wait for an unknown amount of time? It would seem
> > that this would do it:
> >
> > trap("CLD") {
> >   pid = Process.wait
> >   puts "Child pid #{pid}: terminated"
> > }
> >
> > 1.upto(4) do
> >   fork do
> >     exec("sleep 3 && echo \"hello $HOSTNAME #{Process.pid}\n\"")
> >   end
> > end
> >
> > Process.waitall
>
>   puts Process.waitall
>
> =begin ri_output
> ------------------------------------------------------- Process::waitall
>      Process.waitall   => [ [pid1,status1], ...]
> ------------------------------------------------------------------------
>      Waits for all children, returning an array of _pid_/_status_ pairs
>      (where _status_ is a +Process::Status+ object).
>         [...]
> =end
>
>   # So while I'm not sure what's happening to the missing signal
>   # you should be able to see that all the processes have finished.
> >
> > But trap isnt always called on all the children.
>
> >
> > Example output:
> >
>         [...]
> > Notice that 4137 never called the trap callback even though
> > Process.waitall was called.
> > 
>         Hugh