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Investigating stalled pipes (provoked by t/io/eintr.t hanging)

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From:
Tom Hukins
Date:
July 4, 2011 06:11
Subject:
Investigating stalled pipes (provoked by t/io/eintr.t hanging)
Message ID:
20110704131137.GS6118@eborcom.com
Hi,

Recently t/io/eintr.t has highlighted problems with pipes and perl on FreeBSD
and a few other operating systems.  On FreeBSD, these tests began stalling
after a commit that increased PERLIOBUF_DEFAULT_BUFSIZ to of 8192 bytes:
http://perl5.git.perl.org/perl.git/commit/b83080de5c4254

The most recent discussion happened here:
http://rt.perl.org/rt3//Public/Bug/Display.html?id=92828

Older discussions happened here:
http://rt.perl.org/rt3/Public/Bug/Display.html?id=85842

I decided to investigate, but had trouble understanding which part of perl's
source code implements pipes after a brief look.  After this, I wrote a short C
program that I hoped would demonstrate the problems with stalling pipes (see
attached file).  I could not reproduce the problem, so it seems to me that the
fault lies somewhere within perl, not FreeBSD.  However, I lack confidence with
C, so please review my program and check I made no mistakes.

Please let me know if I can do any more to help track down what's going on.

Tom

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