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From: dce@mips.UUCP (David Elliott)
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.bugs.4bsd
Subject: Re: Running stdin/out through a pipe to a child process
Message-ID: <145@quacky.mips.UUCP>
Date: Mon, 19-Jan-87 10:43:50 EST
Article-I.D.: quacky.145
Posted: Mon Jan 19 10:43:50 1987
Date-Received: Thu, 22-Jan-87 03:44:21 EST
References: <136@cogent.UUCP> <3112@rsch.WISC.EDU> <423@bobkat.UUCP>
Reply-To: dce@quacky.UUCP (David Elliott)
Distribution: world
Organization: MIPS Computer Systems, Sunnyvale, CA
Lines: 30
Summary: Bug in 4.[23]BSD with closing pipes
Xref: mnetor comp.unix.questions:787 comp.unix.wizards:675 comp.bugs.4bsd:140

With all of this discussion about pipes, I thought I'd bring up the
subject of a (4.[23]BSD) bug involving closing two pipes in succession:

1. A pipe is opened, written to, closed, and the child process is waited on.
After termination, this is done again. All goes as expected.

2. Two pipes are opened and written to. Next, both pipes are closed. Finally,
each child process is waited for. All goes as expected, except that I
find it odd that the second child is found by wait() first. This really
isn't the problem anyway.

3. Two pipes are opened and written two. Afterwards, each pipe is closed and
the child process waited for (that is, pipe 1 is closed and child 1 is
waited for and then pipe 2 is closed and child 2 is waited for). In this
case, the first wait() blocks, and the first child never terminates except
when the parent does.

I have reduced these 3 cases as much as possible by inlining the code for
popen() and pclose() and getting rid of the stdio code used by them (stdio
exists only to print error messages in the programs). The result is a set
of programs that directly call the system calls involved.

If anyone would like to work on this problem, I can send out copies of
these programs (the whole deal is about 8K of source, but I didn't want
to clutter up the net).

-- 
			David Elliott

UUCP: 	{decvax,ucbvax,ihnp4}!decwrl!mips!dce, DDD:  	408-720-1700