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From: marlon@daisy.UUCP (Marlon Pearson)
Newsgroups: comp.unix.questions
Subject: Re: parent & child reading stdin
Message-ID: <48@daisy.UUCP>
Date: 2 May 90 16:38:24 GMT
References: <46@daisy.UUCP> <7940@jpl-devvax.JPL.NASA.GOV>
Reply-To: marlon@daisy.com (Marlon Pearson)
Distribution: usa
Organization: Daisy/Cadnetix
Lines: 40

:In article <46@daisy.UUCP> marlon@daisy.UUCP (Marlon Pearson) writes:
:: My understanding is that you can't guarantee who gets which bytes when
:: you have two processes reading from the stdin at the same time. Is it a 
:: bad idea if I have a parent process that will read the first N bytes and then
:: fork and exec a child process and let it read the rest of stdin? I have tried
:: this with out doing any dups or pipes or such for passing bytes from the
:: parent to the child. The child inherits the stdin from its parent and reads
:: it fine. As I said, it seems to work and makes sense but is it the "correct"
:: way of doing it.

:It better be correct, since the shells do that all day long.

:The distinction to be made is that, since "correct" programs are using the
:fork as a synchronization point, they are NOT, in fact, "two processes
:reading from stdin at the same time."

:Though I don't know what you mean by your antepenultimate sentence.  In
:what way are you using stdin to pass bytes from the parent to the child?
:That doesn't fit in with the rest of what you are asking.

:Larry Wall

Larry,

Thanks for the response.
As to the third from the end sentence. I understand that it is a fairly common
practice when passing info between a parent and child to set up a pipe or pipes
where one process writes to the pipe and the other reads from it. So, I thought
this may be an alternative to what I current have working. The parent would read
from stdin and after it had consumed the first N bytes it would simply pass the
remaining byte stream to the child via writing to the pipe. The child would read
from the pipe instead of stdin.

Marlon


-- 
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Marlon
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