[Omp] atomic directive semantics

[Dieter an Mey]

Why can't we just go abandon atomic and let the compiler try to optimize 
the critical region?

Dieter


Richard Henderson wrote:

> On Thu, Sep 22, 2005 at 03:06:14PM -0700, Shah, Sanjiv wrote:
> 
>>The OpenMP specifications have been written in a way that allows an
>>implementation the freedom to degrade a proper set of atomics to
>>critical sections based on the HW and SW support available.
> 
> 
> Hmm.  But since readers don't use #pragma omp atomic, critical
> sections for writers only are by themselves are not sufficient.
> The platform must have an atomic store instruction for the data
> type; otherwise a reader can read a partial update.
> 
> So while this is certainly possible for long double on i386,
> but not powerpc.  And it isn't possible for complex long double
> on any platform.
> 
> 
>>Our intention was integer and real, and perhaps complex.  Pointer can
>>also be done easily.  It's really up to each implementation.
>>
>>I hope that answers your question.
> 
> 
> Not really.  If it's up the the implementation, then the specification
> should use fuzzier language.  If it isn't, then a little clarification
> would be nice.
> 
> While I was pondering the problem, I downloaded the Intel compiler,
> and see that it simply punts and doesn't allow complex data types.
> So perhaps that's good enough -- there isn't a code base that relies
> on such things working.
> 
> 
> r~
> 
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Dieter an Mey
High Performance Computing               Hochleistungsrechnen
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