Re: [boost] [lock-free] CDS -yet another lock-free library

Subject: Re: [boost] [lock-free] CDS -yet another lock-free library
From: Helge Bahmann (hcb_at_[hidden])
Date: 2010-03-30 05:08:11

On Tue, 30 Mar 2010, Khiszinsky, Maxim wrote:

> Helge Bahmann wrote:
>
>> Sure, if you turn optimization off, code looks ridiculous. Both gcc
>> (tested with various versions ranging from 3.3 to 4.4) and msvc (visual
>> studio express) optimize the switch/case with constant operand into
>> nothingness.
>
> Sorry, the problem observed on MS VC++ 2008 x86 with full optimization 
> and SSE instruction set. See my previous answer to Phil with 
> explanations.

I see, and I would wager to guess that the problem with the following:

         atomic64_t v ;
         v = _mm_loadl_epi64( (__m128i *) pMem ).m128i_i64[0] ;

are the funky type-casts confusing aliasing analysis sufficiently so that 
the compiler believes that "order" might be modified by the 
above statements.

You could try changing that to something like:

         __m128i i = _mm_loadl_epi64( (__m128i * _Restrict) pMem);
         if (order == ...) ...
         return i.m128i_i64[0];

I can assure you that MSVC does not have an "intrinsic" problem with 
making the desired optimization (at least I know of no such problem with 
Boost.Atomic).

>> I would however be very interested in sparc and ia64 atomic operations,
>> would you be interested in implementing (or lending me a hand) them for
>> boost.atomic?
>
> You may try CDS implementation of sparc and ia64 atomics:
>  cds\compiler\gcc\ia64\atomic.h - for itanium ia64
>  cds\compiler\gcc\sparc\atomic.h - for sparc 64bit mode
> These files contain template and common versions of 32bit and 64bit 
> atomic primitives.
>
> If you need I can extract it from CDS for you, no problem.
> It works well with CDS tests but I'm not sure whether it is correct...

Thanks will look into that and send you a version for testing

Best regards
Helge