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instance counter

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  instance counter Moshbear dot Net <moshbear.net@gmail.com> - 2011-06-11 15:08 -0700
    Re: instance counter "Chris M. Thomasson" <cristom@charter.net> - 2011-06-11 15:43 -0700
      Re: instance counter Moshbear dot Net <moshbear.net@gmail.com> - 2011-06-11 15:58 -0700
        Re: instance counter Pete Becker <pete@versatilecoding.com> - 2011-06-11 14:01 -1000
          Re: instance counter "Chris M. Thomasson" <cristom@charter.net> - 2011-06-11 19:52 -0700
            Re: instance counter Moshbear dot Net <moshbear.net@gmail.com> - 2011-06-12 03:17 -0700
              Re: instance counter Paavo Helde <myfirstname@osa.pri.ee> - 2011-06-18 06:41 -0500

#6632 — instance counter

Given
class Fred {
public:
    Fred() {
      ctr = ++xctr;
    }
...
private:
    unsigned ctr;
    static unsigned xctr; // initialized via boost::thread::run_once
...
};
,
what would be the best way to make the increment-and-read of xctr
atomic so that it is thread-safe?
I'm using xctr to track instance number of class so that I can use
operator<(const Fred&) to compare by instance-creation time.

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#6634

"Moshbear dot Net" <moshbear.net@gmail.com> wrote in message 
news:ccf39133-e576-456d-9ee2-66f9bebdf8aa@d14g2000yqb.googlegroups.com...
> Given
> class Fred {
> public:
>    Fred() {
>      ctr = ++xctr;
>    }
> ...
> private:
>    unsigned ctr;
>    static unsigned xctr; // initialized via boost::thread::run_once
> ...
> };
> ,
> what would be the best way to make the increment-and-read of xctr
> atomic so that it is thread-safe?

Perhaps an atomic fetch-and-add operation, or a statically initialized 
PThread mutex.


> I'm using xctr to track instance number of class so that I can use
> operator<(const Fred&) to compare by instance-creation time.

What happens when that "version counter" wraps around?

;^) 

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#6637

On Jun 11, 6:43 pm, "Chris M. Thomasson" <cris...@charter.net> wrote:
> "Moshbear dot Net" <moshbear....@gmail.com> wrote in messagenews:ccf39133-e576-456d-9ee2-66f9bebdf8aa@d14g2000yqb.googlegroups.com...
>
> > Given
> > class Fred {
> > public:
> >    Fred() {
> >      ctr = ++xctr;
> >    }
> > ...
> > private:
> >    unsigned ctr;
> >    static unsigned xctr; // initialized via boost::thread::run_once
> > ...
> > };
> > ,
> > what would be the best way to make the increment-and-read of xctr
> > atomic so that it is thread-safe?
>
> Perhaps an atomic fetch-and-add operation, or a statically initialized
> PThread mutex.

Is there a portable way of doing
atomic {
  ++xctr;
  ctr = xctr;
}

Also, it looks like I'm going to have to search the boost docs for
mutex-locked statically-scoped counters.
However, I believe that somebody has already done this and can offer
guidance as to which boost class is
preferred (or c++0x/tr1 class, given that this is c.l.c++ :)

>
> > I'm using xctr to track instance number of class so that I can use
> > operator<(const Fred&) to compare by instance-creation time.
>
> What happens when that "version counter" wraps around?

I'd be using ::uint64_t in actual code. This was just to show the
concept.

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#6639

On 2011-06-11 12:58:12 -1000, Moshbear dot Net said:

> 
> Is there a portable way of doing
> atomic {
>   ++xctr;
>   ctr = xctr;
> }
> 

std::atomic<int> xctr = 0;

and

ctr = ++xctr;

That's with C++11; your library might already have it.

-- 
  Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The 
Standard C++ Library Extensions: a Tutorial and Reference 
(www.petebecker.com/tr1book)

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#6641

"Pete Becker" <pete@versatilecoding.com> wrote in message 
news:2011061114015396183-pete@versatilecodingcom...
> On 2011-06-11 12:58:12 -1000, Moshbear dot Net said:
>
>>
>> Is there a portable way of doing
>> atomic {
>>   ++xctr;
>>   ctr = xctr;
>> }
>>
>
> std::atomic<int> xctr = 0;

[...]

Want it NOW!

http://www.stdthread.co.uk

:^) 

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#6651

On Jun 11, 10:52 pm, "Chris M. Thomasson" <cris...@charter.net> wrote:
> "Pete Becker" <p...@versatilecoding.com> wrote in message
>
> news:2011061114015396183-pete@versatilecodingcom...
>
> > On 2011-06-11 12:58:12 -1000, Moshbear dot Net said:
>
> >> Is there a portable way of doing
> >> atomic {
> >>   ++xctr;
> >>   ctr = xctr;
> >> }
>
> > std::atomic<int> xctr = 0;
>
> [...]
>
> Want it NOW!
>
> http://www.stdthread.co.uk
>
Any F/OSS versions? boost::interprocess::detail has atomic operations,
but it looks a bit ugly to use in end-user code.
And <atomic> is c++0x (existence in: g++ 4.5 and higher, likely in VC
1x (not in VC10)).

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#6874

Moshbear dot Net <moshbear.net@gmail.com> wrote in news:e05a0698-2305-479b-
bf2f-3659ddbd86a4@b1g2000yql.googlegroups.com:

>> >> Is there a portable way of doing
>> >> atomic {
>> >>   ++xctr;
>> >>   ctr = xctr;
>> >> }
[...]
> Any F/OSS versions? boost::interprocess::detail has atomic operations,
> but it looks a bit ugly to use in end-user code.

In C++ one encapsulates such things in a little class which can then be 
(re)used easily in the "end-user code". 

hth
Paavo

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