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From: Zoltan Hidvegi <hzoli@ny.frontiercomm.net>
Message-Id: <199705151547.LAA00880@hzoli.home>
Subject: Re: stopping "wait" in (sub)script ?
In-Reply-To: <970515035240.ZM381@candle.brasslantern.com> from Bart Schaefer at "May 15, 97 03:52:39 am"
To: zsh-workers@math.gatech.edu (Zsh hacking and development)
Date: Thu, 15 May 1997 11:47:16 -0400 (EDT)
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> On May 15, 11:07am, Peter Stephenson wrote:
> } This doesn't seem to fix this particular bug here, it's still
> } uninterruptible.  On the other hand, replacing `cat ss` with $(<ss)
> } has always worked.  That doesn't leave much code in getoutput() to
> } make the difference.
> 
> I think the problem must be in signal_suspend().  The only difference
> between the two cases in getoutput() is that $(<ss) does an explicit
> child_unblock(), whereas `cat ss` does it implicitly via child_suspend(0).
> 
> If you go look at signal_suspend(), you'll find a lot of #ifdefs for the
> assorted signal handling variations.  I'll bet this problem is specific
> to one or more of those variations.

No.  The problem is that $(...) does not enter the new process to the
process table.  $(<...) does not fork, so it is not surprising that it
works.  The problem is that `cat ss` forks, and does an entersubsh after
the fork().  When a process terminates the SIGCHLD handler calls
update_job, which should reattach the terminal, but it does not do that
since the terminated job was not in the process table so update_job() is
not even called :-(.  I'll try to figure out a better solution tonight
(by that time it'll be tomorrow in Europe).

Zoltan