From: Paolo Bonzini <pbonzini@redhat.com>
To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: "kwolf@redhat.com" <kwolf@redhat.com>,
"aliguori@linux.vnet.ibm.com" <aliguori@linux.vnet.ibm.com>,
"sw@weilnetz.de" <sw@weilnetz.de>,
"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
"stefanha@linux.vnet.ibm.com" <stefanha@linux.vnet.ibm.com>
Subject: Re: [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore
Date: Mon, 16 Jul 2012 16:03:20 +0200 [thread overview]
Message-ID: <50041F28.3030203@redhat.com> (raw)
In-Reply-To: <50041CE7.80501@siemens.com>
Il 16/07/2012 15:53, Jan Kiszka ha scritto:
>> >
>> > qemu_cond_wait only uses WaitForSingleObject with INFINITE timeout, and
>> > the algorithm relies on that.
> I see. But this doesn't look complex awfully. Just move the waker
> signaling from within cond_wait under the mutex as well, maybe add
> another flag if there is really someone waiting, and that's it. The
> costs should be hard to measure, even in line of code.
There is still a race after WaitForSingleObject times out. You need to
catch the mutex before decreasing the number of waiters, and during that
window somebody can broadcast the condition variable.
I'm not saying it's impossible, just that it's hard and I dislike
qemu_cond_timedwait as much as you dislike semaphores. :)
Paolo
next prev parent reply other threads:[~2012-07-16 14:03 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-16 10:42 [Qemu-devel] [PATCH 00/12] Portable thread-pool/AIO, Win32 emulated AIO Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 01/12] event_notifier: enable it to use pipes Paolo Bonzini
2012-07-19 18:58 ` Anthony Liguori
2012-07-16 10:42 ` [Qemu-devel] [PATCH 02/12] event_notifier: add Win32 implementation Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 03/12] main-loop: use event notifiers Paolo Bonzini
2012-07-19 19:04 ` Anthony Liguori
2012-07-16 10:42 ` [Qemu-devel] [PATCH 04/12] aio: provide platform-independent API Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 05/12] aio: add Win32 implementation Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 06/12] linux-aio: use event notifiers Paolo Bonzini
2012-07-19 19:10 ` Anthony Liguori
2012-07-16 10:42 ` [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore Paolo Bonzini
2012-07-16 12:00 ` Jan Kiszka
2012-07-16 12:01 ` [Qemu-devel] [PATCH] qemu-thread: Introduce qemu_cond_timedwait for POSIX Jan Kiszka
2012-07-16 13:20 ` [Qemu-devel] [PATCH 07/12] qemu-thread: add QemuSemaphore Paolo Bonzini
2012-07-16 13:34 ` Jan Kiszka
2012-07-16 13:35 ` Paolo Bonzini
2012-07-16 13:53 ` Jan Kiszka
2012-07-16 14:03 ` Paolo Bonzini [this message]
2012-07-16 14:09 ` Jan Kiszka
2012-07-16 14:20 ` Paolo Bonzini
2012-07-24 16:55 ` Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 08/12] aio: add generic thread-pool facility Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 09/12] block: switch posix-aio-compat to threadpool Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 10/12] raw: merge posix-aio-compat.c into block/raw-posix.c Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 11/12] raw-posix: rename raw-posix-aio.h, hide unavailable prototypes Paolo Bonzini
2012-07-16 10:42 ` [Qemu-devel] [PATCH 12/12] raw-win32: add emulated AIO support Paolo Bonzini
2012-07-23 16:35 ` Blue Swirl
2012-07-23 16:59 ` Paolo Bonzini
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