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Re: "volatile" on variables and current processors

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On 8/20/2019 11:02 PM, Paavo Helde wrote:
> On 20.08.2019 23:58, Vir Campestris wrote:
>>
>> I know what the code ought to be. It ought to be re-written in C++ using
>> atomics (and in several cases other library features - I noticed a
>> spin-lock)
>>
>> But it's big. It isn't going to be rewritten unless it's proved to be a
>> problem. And proving this would be hard - it'll be a race condition
>> somewhere.
> 
> Race conditions are not so hard to demonstrate, especially when you know 
> where the problem is. Just make a volatile integer counter with initial 
> value one, then let your 4 cores increase and decrease it in tight loops 
> in parallel. Whenever the counter drops to zero or below you have 
> demonstrated the race condition. 

Indeed. :^)


> Should happen in seconds or minutes, 
> but my experience is from Intel, not ARM, so YMMV.
> 
> BTW, the above is an extract from a real life scenario where the counter 
> mimics a smartpointer reference counter. In real life the effects are 
> much more fun - the pointed object will be released when the refcount 
> drops to zero, so the next non-trivial member function call to it will 
> probably segfault. This kind of behavior might make the demo a bit more 
> convincing ;-)
> 


Kind of reminds me of creating a rng using race-condition's:

https://groups.google.com/d/topic/comp.lang.c++/7u_rLgQe86k/discussion

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"volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-19 21:56 +0100
  Re: "volatile" on variables and current processors red floyd <dont.bother@its.invalid> - 2019-08-19 15:20 -0700
    Re: "volatile" on variables and current processors red floyd <dont.bother@its.invalid> - 2019-08-19 15:21 -0700
      Re: "volatile" on variables and current processors "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-08-19 16:37 -0700
        Re: "volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-20 21:58 +0100
          Re: "volatile" on variables and current processors scott@slp53.sl.home (Scott Lurndal) - 2019-08-20 22:18 +0000
            Re: "volatile" on variables and current processors Vir Campestris <vir.campestris@invalid.invalid> - 2019-08-22 21:39 +0100
          Re: "volatile" on variables and current processors Paavo Helde <myfirstname@osa.pri.ee> - 2019-08-21 09:02 +0300
            Re: "volatile" on variables and current processors "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2019-08-20 23:10 -0700
          Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-21 08:34 +0200
            Re: "volatile" on variables and current processors Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-21 20:39 +0100
              Re: "volatile" on variables and current processors Chris Vine <chris@cvine--nospam--.freeserve.co.uk> - 2019-08-21 21:02 +0100
              Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-22 13:30 +0200
        Re: "volatile" on variables and current processors Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-21 08:43 +0200
      Re: "volatile" on variables and current processors "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com> - 2019-08-20 02:22 +0200
        Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 10:05 +0200
    Re: "volatile" on variables and current processors Keith Thompson <kst-u@mib.org> - 2019-08-19 17:08 -0700
  Re: "volatile" on variables and current processors Bonita Montero <Bonita.Montero@gmail.com> - 2019-08-20 06:08 +0200
  Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 10:14 +0200
  Re: "volatile" on variables and current processors Juha Nieminen <nospam@thanks.invalid> - 2019-08-20 13:03 +0000
    Re: "volatile" on variables and current processors David Brown <david.brown@hesbynett.no> - 2019-08-20 16:18 +0200

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