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

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Subject: Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle terminating signals.
From: Avi Kivity <avi@xxxxxxxxxxxx>
Date: Tue, 26 Aug 2008 19:12:07 +0300
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Gerd Hoffmann <kraxel@xxxxxxxxxx>
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Ian Jackson wrote:
Avi Kivity writes ("Re: [Xen-devel] Re: [Qemu-devel] [PATCH 01/13] Handle 
terminating signals."):
Ian Jackson wrote:
My experience suggests very strongly that we should avoid doing
multithreaded things if at all possible.  Threads are less portable;
even when they are provided many of the implementations are buggy
(although less so nowadays).

There is also the way that once you have a multithreaded program, it
is much more difficult to discourage the expansion of the concurrent
functionality until the whole program is a mass of race bugs.  I would
rather not open this stable door.
In this case the thread is only used to emulate the signalfd() system call; it is not part of qemu proper.

That doesn't make us any less exposed to bugs in the threading
implementation, and is only of marginal use if anything for explaining
to people why we shouldn't have a Windows-style multithreaded bug

Threading bugs in the implementation?  In 2008?

Practically all serious software is multithreaded nowadays.

Also, I think messing about with Linux-specific syscalls and then
emulating them is hardly a sensible way to carry on, when the
alternative is portable and simple.

This has merit; though signalfd() will be a lot faster than catching a signal and writing to a pipe.

In particular, delivering a signal to userspace has to save the floating point context, while signalfd() avoids it. With the signals used to signal I/O completion, this matters.

error compiling committee.c: too many arguments to function

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