From: TYann AT vet DOT com DOT au (Trevor Yann)
Subject: Re: spawn problems (windows 98?)
4 Aug 1998 00:28:13 -0700
Message-ID: <3.0.5.32.19980804165143.007de820.cygnus.cygwin32.developers@mail.mel.cybec.com.au>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
To: cygwin32-developers AT cygnus DOT com

After some more detective work, I managed to get a stack trace at the time
of the hang.

The stack looks like this:
(tos)	block_sig_dispatch
	proc_subproc
	wait4
	waitpid
	waitchld (function in bash)
	sigchld_handler (function in bash)
	call_handler
	?
	?
	CreateProcessA
	spawn_guts
	spawnve
	spawnv
	execute_simple_command (bash function)

What has happened is a child process has died whilst CreateProcess is
creating a new process. Bash handles SIGCHLD by (eventually) calling waitpid.

Normally this won't happen, because bash blocks usually signals before
calling fork. My modifications now block signals before calling spawnv. Net
result is that I don't see the problem anymore.

Is bash misbehaving by calling waitpid from within a signal processing
function?

I guess that the sig_dispatch mutex is being grabbed somewhere before the
processing of SIGCHLD, but I can't see where.

If we are to support this sort of scenario, then we'll have to make some
changes to protect against the problem.