[Omp] A question about threadprivate

[Dieter an Mey]

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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> 

-- 
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Dieter an Mey
High Performance Computing               Hochleistungsrechnen
RWTH Aachen University                   Rechen- und Kommunikations-
Center for Computing and Communication   zentrum der RWTH Aachen
phone: ++49-(0)241-80-24377              Seffenter Weg 23
fax:   ++49-(0)241-80-22134              52074 Aachen, Germany
email: anmey at rz.rwth-aachen.de
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