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Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating signal

From: Ian Jackson
Subject: Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating signals.
Date: Thu, 28 Aug 2008 10:34:05 +0100

Jamie Lokier writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle 
terminating signals."):
> A quick read of Glibc 2.3.1 source says its AIO code does not change
> the signal mask when it creates an AIO handling thread.

Thanks for investigating that.

> (This might be a Glibc bug - threads you don't know about shouldn't be
> receiving your signals, should they?)

Yes, it's a bug.  (I wonder why my test program didn't expose it.)

> That means if it wasn't masked when you issued the first AIO request,
> it won't be masked in that thread.

In practice since we use aio this probably means we can't rely on
signal blocking except for signals which qemu keeps blocked `nearly
all' the time.  So pipe-to-self in the signal handler is the way to

> It's quite annoying that POSIX threads doesn't provide any way to say
> "mask this signal in all other threads", which you often want to do
> from a library.

That too.


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