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

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-07-16 15:35, Paolo Bonzini wrote:
> Il 16/07/2012 15:34, Jan Kiszka ha scritto:
>> On 2012-07-16 15:20, Paolo Bonzini wrote:
>>> Il 16/07/2012 14:00, Jan Kiszka ha scritto:
>>>> 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 can do that (or just use pthreads-win32), but only at the cost of
>>> making cond_wait() slower and more complex.
>>
>> Why will it affect cond_wait? WaitForSingleObject can time out as well.
> 
> 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.

Jan

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