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Re: fun with a mutex...

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From cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups comp.lang.c++
Subject Re: fun with a mutex...
Date Wed, 13 Aug 2025 11:45:42 -0000 (UTC)
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Originator cross@spitfire.i.gajendra.net (Dan Cross)
Xref csiph.com comp.lang.c++:122524

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In article <107eu5g$33jcr$5@dont-email.me>,
Chris M. Thomasson <chris.m.thomasson.1@gmail.com> wrote:
>On 8/12/2025 1:23 AM, Bonita Montero wrote:
>> Am 11.08.2025 um 22:30 schrieb Chris M. Thomasson:
>> 
>>> I gave some quick examples, perhaps you missed them. It could be 
>>> batching thread local queues, checking to see if an 
>>> GetQueuedCompletionStatusEx (timeout 0) succeeds, ...
>> 
>> GetQueuedCompletionStatusEx() is an expensive kernel call, not something
>> you do casually. Even a Sleep( 0 ), which is equivalent to a std::
>> this_thread::yield(), costs about 1,000 clock cycles on a modern CPU.
>> And GetQueuedCompletionStatusEx() isn't a function whose execution can
>> be arbitrarily delayed or even prevented altogether. In other words:
>> You're simply overthinking.
>
>Its seems quite fine though. try_lock fails... Sometimes go for a 
>GetQueuedCompletionStatusEx with a 0 timeout. Vs just going into the 
>kernel anyway for the contention. Try some local queues before trying 
>GetQueuedCompletionStatusEx a couple of times in the backoff, Or 
>spinning ala adaptive mutex logic doing nothing anyway... If it succeeds 
>we get to sort the results into their per thread queues, if not, we 
>lock. If it succeeds too (too much work) many times we lock. If try lock 
>does not fail, well we got the damn lock anyway. So be it?

I don't think you have a good handle on the relative cost of
these operations.

You seem to be against spending a few cycles spinning, or
against paying the one time cost of going to sleep in the kernel
until your mutex is available, but willing to burn thousands of
cycles going into the kernel over and over again to see if an IO
port becomes ready so that you can keep your thread "hot".

That's, frankly, not at all a good tradeoff.

	- Dan C.

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fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-07-29 22:54 -0700
  Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-02 12:58 -0700
    Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-02 13:00 -0700
    Re: fun with a mutex... Muttley@DastardlyHQ.org - 2025-08-04 08:48 +0000
      Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-04 12:34 -0700
        Re: fun with a mutex... Muttley@DastardlyHQ.org - 2025-08-05 07:27 +0000
          Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-05 16:10 -0700
            Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-06 00:38 +0000
              Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-05 19:14 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-06 11:29 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-06 15:43 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-08 01:41 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 20:52 -0700
              Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-05 19:16 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-06 12:04 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-06 15:47 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-08 01:49 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 20:59 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-09 09:17 +0000
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-09 11:52 +0200
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-09 16:08 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-09 10:48 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-10 03:08 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-11 13:37 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-13 11:41 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-15 17:28 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 20:25 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 13:34 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 20:39 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 14:06 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 14:28 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 14:33 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 22:56 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 16:09 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 23:44 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 16:55 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 23:57 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-19 13:25 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-15 17:30 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 20:26 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 13:39 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-18 20:44 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 14:08 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 16:11 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-18 16:20 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-11 11:04 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-11 13:30 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-12 10:23 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-12 01:31 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-12 10:39 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-12 01:45 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-12 10:56 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-12 02:14 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-12 15:08 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-15 21:36 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-16 10:13 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-16 01:56 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-16 11:05 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-16 13:31 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-17 14:50 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-17 13:43 -0700
                Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-13 11:45 +0000
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-13 19:07 +0200
                Re: fun with a mutex... scott@slp53.sl.home (Scott Lurndal) - 2025-08-13 17:31 +0000
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-15 10:00 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-13 12:41 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-09 10:44 -0700
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-09 11:00 -0700
        Re: fun with a mutex... "Fred. Zwarts" <F.Zwarts@HetNet.nl> - 2025-08-05 10:27 +0200
          Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-05 16:07 -0700
            Re: fun with a mutex... "Fred. Zwarts" <F.Zwarts@HetNet.nl> - 2025-08-06 10:56 +0200
              Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-06 15:36 -0700
      Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-04 12:38 -0700
        Re: fun with a mutex... Muttley@DastardlyHQ.org - 2025-08-05 07:29 +0000
          Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-05 16:08 -0700
  Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-06 15:51 +0200
    Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-06 15:34 -0700
      Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-07 06:44 +0200
        Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 12:17 -0700
          Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-07 21:51 +0200
            Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 12:52 -0700
              Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-16 11:21 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-16 13:22 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-17 03:59 +0200
                Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-16 23:53 -0700
                Re: fun with a mutex... Bonita Montero <Bonita.Montero@gmail.com> - 2025-08-17 10:37 +0200
        Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 12:32 -0700
      Re: fun with a mutex... cross@spitfire.i.gajendra.net (Dan Cross) - 2025-08-08 01:51 +0000
        Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 21:01 -0700
          Re: fun with a mutex... "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2025-08-07 21:08 -0700

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