From: Robert Klemme <shortcutter@...>
Date: 2009-12-30T06:15:04+09:00
Subject: Re: IO.popen('-') === fork ?

On 12/29/2009 09:54 PM, Nilez Parker wrote:
>> fork does nothing to redirect stdin, stdout and stderr while popen in
>> the form you used will send the sub process's stdout to a pipe.  So
>> the answer is: no, they are not equivalent.  Rather popen uses some
>> form of fork under the hood.
> 
> Thanks Robert. I think I meant to ask whether Process.popen uses the 
> same OS fork call as Process.fork does.
> 
> I found what I need for now though, so I'm posting it partly just for 
> people who find this via google later on. I wanted some pipes between 
> parent and children, and this is what I came up with:
> 
>   children = []
>   3.times do
>     from_child, to_parent = IO.pipe
>     from_parent, to_child = IO.pipe
>     fork do
>       # don't need to read from or write to child
>       to_child.close
>       from_child.close
>       to_parent.write "READY"
>       loop { ... }
>     end
>     children << to_child
>     # don't need to read from or write to parent
>     to_parent.close
>     from_parent.close
>   end
>   # Now the parent has a read/write IO pair for each child stored in 
> `children'; each child has a read/write IO pair for the parent.

I don't see why you go through this instead using one of the #popen 
family of methods (there is also #popen3).

> Thanks Robert for the quick answer, and I'm still curious whether 
> Process.popen uses the same OS fork call as Process.fork does.

Underneath it is eventually the same, yes.

Kind regards

	robert

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