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Subject: Re: [boost] [thread] Timed waits in Boost.Thread potentially fundamentally broken on Windows (possibly rest of Boost too)
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2015-01-25 05:21:12

Le 24/01/15 15:18, Niall Douglas a écrit :
> On 23 Jan 2015 at 18:30, Andrey Semashev wrote:
>>> Vista made these changes to scheduling for efficiency purposes. I
>>> suspect Boost.Thread was written for an XP or earlier target.
>> I'm confused. Boost.Thread always implemented the standard behavior, with
>> possibility of spurious wakeups. Windows before Vista did not exhibit spurious
>> wakeups (which was ok) and since Vista it started doing this, and this
>> improved efficiency (I assume, the estimate of the improvement had included
>> the negative effect on the applications dealing with the wakeups).
>> Boost.Thread is still behaving correctly wrt the standard. So, why would you
>> want to change Boost.Thread and conceal spurious wakeups, making it less
>> efficient? I'll reiterate that any current use of cv must deal with spurious
>> wakeups already.
> Firstly, my thanks to both you and Peter for your thoughts on this.
> After sleeping on it for a night, this is what I'll do: I'm going to
> update Thread's clamping of timeouts to better match Windows since
> Vista onwards. This basically means asking Windows what its current
> scheduling quantum is (it can vary from moment to moment according to
> what applications request) and clamping the timeout sent to Windows
> APIs to that quantum. Therefore, if you asked for a 10ms timeout,
> Thread will clamp that probably to 15 ms before sending it onto
> Windows. I'll always round upwards, so there is a greater potential
> for a timed wait to take one quantum longer than it should before
> timing out, but then that can happen anyway at any time.
> None of this will remove spurious wakeups, but it will reduce their
> frequency considerably. It means that the CPU spends more time
> sleeping and less being woken up and being put back to sleep by a
> predicate check loop.
> If anyone has a problem with this solution, now is the time to speak.
Niall, could we first fix the incoherences you have identified
respecting the standard specification and then see if we need to do
something else.


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