[Omp] A question about threadprivate

[Meadows, Lawrence F]

In the first example? 

-----Original Message-----
From: Dieter an Mey [mailto:anmey at rz.rwth-aachen.de] 
Sent: Wednesday, April 11, 2007 9:43 AM
To: Meadows, Lawrence F
Cc: Marina Kraeva; omp at openmp.org
Subject: Re: [Omp] A question about threadprivate

Data race !

Dieter

Meadows, Lawrence F schrieb:
> I think that the standard specifies what you expect in the first
> example. It makes no guarantee about the second example.
> 
> -----Original Message-----
> From: omp-bounces at openmp.org [mailto:omp-bounces at openmp.org] On Behalf
> Of Marina Kraeva
> Sent: Wednesday, April 11, 2007 9:16 AM
> To: omp at openmp.org
> Subject: [Omp] A question about threadprivate
> 
> Hello,
> 
> Could you please share your opinion on what will happen in the
following
> 
> two small examples.
> 
> In the OpenMP API 2.5 (and in the earlier versions) it is said:
> "The values of data in the threadprivate objects of threads other than

> the initial thread are guaranteed to persist between two consecutive 
> active parallel regions only if all the following conditions hold:
> * Neither parallel region is nested inside another parallel region..."
> 
> 
> According to API, is it guaranteed that in the following example the 
> values of 'i' will persist, so array will have values (0,1,2,3)?
> 
> int i,array(0:3)
> threadprivate(i)
> !$omp parallel num_threads(4)
> 	i=omp_get_thread_num()
> 	!$omp parallel num_threads(2)
> 		... ('i' is not referenced)
> 	!$omp end parallel
> !$omp end parallel
> 
> !$omp parallel num_threads(4) shared(array)
> 	array(omp_get_thread_num())=i
> !$omp end parallel
> 
> 
> 
> What if inside the nested parallel region 'i' was modified:
> 
> int i,array(0:3)
> threadprivate(i)
> !$omp parallel num_threads(4)
> 	i=omp_get_thread_num()
> 	!$omp parallel num_threads(2)
>                 i=-omp_get_thread_num()
> 	!$omp end parallel
> !$omp end parallel
> 
> !$omp parallel num_threads(4) shared(array)
> 	array(omp_get_thread_num())=i
> !$omp end parallel
> 
> Is it guaranteed, that array still will have values (0,1,2,3)?
> 
> Thank you!
> Marina Kraeva.
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Dieter an Mey
High Performance Computing               Hochleistungsrechnen
RWTH Aachen University                   Rechen- und Kommunikations-
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