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Date: Wed, 27 Aug 2008 17:27:19 +0100
From: Jamie Lokier <jamie@shareable.org>
Subject: Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating
	signals.
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To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: xen-devel@lists.xensource.com, qemu-devel@nongnu.org, Gerd Hoffmann <kraxel@redhat.com>

Ian Jackson wrote:
> Jamie Lokier writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating signals."):
> > Leading to: why would (real) signals being used to collect AIO events
> > anyway, if you don't have signalfd()?  If you've got a helper thread,
> 
> If you use aio, glibc has a tendency to emulate it with thread(s).
> The helper thread I was referring to in my commit message is the
> glibc-created helper thread.  glibc appears (in strace) to do IO in
> this thread and then raises the signal you asked for (SIGUSR2 in
> qemu's case).

That observation implies Anthony's helper thread will not always
receive the SIGUSR2 signals - Glibc's thread may receive them instead.

So when the signalfd-emulation signal handler writes to the pipe, it
might block Glibc's AIO thread.  Is that ok, Anthony?

-- Jamie