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From: Gottlob Frege <gottlobfrege@gmail.com>
To: Ross Johnson <rpj@callisto.canberra.edu.au>,
	pthreads-win32@sources.redhat.com
Subject: Re: starvation in pthread_once?
Date: Wed, 16 Sep 2009 15:38:00 -0000	[thread overview]
Message-ID: <97ffb310909160838v6671abccv3b230ec213e66057@mail.gmail.com> (raw)
In-Reply-To: <97ffb3105032209269b0f44e@mail.gmail.com>

Blast from the past - whatever happened to changing call_once() to not
create the named mutex when it wasn't needed?


On Tue, Mar 22, 2005 at 1:26 PM, Gottlob Frege <gottlobfrege@gmail.com> wrote:
> If it comes down to it, I might vote for daisy-chaining over
> busy-looping (assuming the busy-looping is endless).  Remember, this
> all started because the original implementation was polling/sleeping
> on 'initted' - and if the busy-looping thread is high-priority, then
> we are locked forever...
>
>
> On Tue, 22 Mar 2005 15:14:07 +1100, Ross Johnson
> <rpj@callisto.canberra.edu.au> wrote:
>> On Mon, 2005-03-21 at 11:07 -0500, Gottlob Frege wrote:
>>
>> > So, it doesn't seem to be getting any easier!  *Almost* to the point
>> > where a big named mutex becomes tempting - there is a lot to be said
>> > for simplicity.  However, my/the goal is still to at least minimize
>> > the non-contention simple init case...
>>
>> I'm less and less tempted to use a named mutex. Perhaps there's a
>> standard technique, but AFAICS it's impossible to guarantee that the
>> name is unique across the system (and all Windows variants).
>>
>> And I agree, minimum overhead for the uncontended case is the top
>> priority (after correct behaviour). I'm not concerned at all about speed
>> in the cancellation case.
>>
>> > And the event is still an auto-reset, although I no longer think it
>> > really matters - I really haven't had the tenacity to think this stuff
>> > through.  If it doesn't matter, manual-reset would be better, I think
>> > - I don't like having 1 thread relying on another thread waking it up,
>> > - for cases where the thread is killed, or strange thread priorities,
>> > etc.
>>
>> It all looks to me like it will work. I don't recall, in the version
>> that's in pthreads-win32 now, why I included eventUsers (++/--) in what
>> you have as the __lock() sections. Maybe to save additional Atomic calls
>> (bus locks). But now I realise [in that version - not yours] that waking
>> threads can block unnecessarily when leaving the wait section.
>>
>> It probably doesn't matter if cancel_event is auto or manual. I think
>> there will be at most one thread waiting on it. And, for 'event', like
>> you I'm uncomfortable with daisy-chaining SetEvent() calls.
>>
>> The only problem with the alternative of using a manual-reset event is
>> that some thread/s may busy-loop for a bit until an explicit reset
>> occurs. It seems untidy, but it's probably more robust than daisy-
>> chained SetEvents given the issues you've identified above.
>>
>> So I'm tempted to leave both events as manual-reset events. I'm also
>> guessing that this busy-looping will be extremely rare - perhaps only
>> when a new thread sneaks in to become initter, then suspends just inside
>> while the first waiter is waking and heading back to the loop start.
>>
>> I'll run your design and let you know the results.
>>
>> Thanks.
>> Ross
>>
>>
>

  parent reply	other threads:[~2009-09-16 15:38 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2005-03-03  9:32 Gottlob Frege
2005-03-04 23:18 ` Ross Johnson
2005-03-08  2:22   ` Ross Johnson
2005-03-08  3:00     ` Gottlob Frege
2005-03-08  6:11       ` Ross Johnson
2005-03-08  9:49         ` Alexander Terekhov
2005-03-08  9:56           ` Alexander Terekhov
2005-03-08  9:58             ` Alexander Terekhov
2005-03-08 16:11               ` Gottlob Frege
2005-03-08 17:14                 ` Alexander Terekhov
2005-03-08 18:28                   ` Gottlob Frege
2005-03-14  2:47                 ` Ross Johnson
     [not found]                   ` <97ffb310503140832401faa2b@mail.gmail.com>
     [not found]                     ` <1110842168.21321.78.camel@desk.home>
     [not found]                       ` <97ffb3105031415473a3ee169@mail.gmail.com>
     [not found]                         ` <1110855601.21321.203.camel@desk.home>
     [not found]                           ` <97ffb31050321080747aa5a7c@mail.gmail.com>
     [not found]                             ` <1111464847.8363.91.camel@desk.home>
     [not found]                               ` <97ffb3105032209269b0f44e@mail.gmail.com>
2009-09-16 15:38                                 ` Gottlob Frege [this message]
2009-09-17  1:28                                   ` Ross Johnson
2005-03-08 16:05       ` Gottlob Frege

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