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Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore
Date: Mon, 16 Jul 2012 14:00:17 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2012-07-16 12:42, Paolo Bonzini wrote:
> The new thread pool will use semaphores instead of condition
> variables, because QemuCond does not have qemu_cond_timedwait.

I'll post an updated patch (according to last round's review comments)
that adds this service for POSIX. I bet you'll find a way to extend it
to Win32 if that is required. ;)

> (I also like it more this way, since semaphores model well the
> producer-consumer problem).

Let's not introduce another synchronization mechanism unless there is a
real need. Semaphores tend to be misused for things they don't fit, so
better keep them out of reach.

Also, if you do producer-consumer this way, you need a down() for every
entity you dequeue. In contrast, you only interact with condition
variables if there the consumer queue is empty - less atomic ops.


Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux

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