[ET Trac] [Einstein Toolkit] #928: openmp parallelization within Exact broken

[Einstein Toolkit]

#928: openmp parallelization within Exact broken
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  Reporter:  knarf                  |       Owner:                     
      Type:  defect                 |      Status:  confirmed          
  Priority:  minor                  |   Milestone:  ET_2012_11         
 Component:  EinsteinToolkit thorn  |     Version:  development version
Resolution:                         |    Keywords:                     
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Comment (by rhaas):

 I don't know if an atomic would help us. The problem is that we would need
 to guarantee that first_call is only updated (in memory) after all the
 other variables have been flushed to memory. Ie the problem is not that
 threads see an inconsistent first_call but that first_call does not match
 status of the other saved variables. A flush would seem to have the same
 problem: we don't know if the compiler might move the first_call setting
 and flushing to the beginning of the block (OpenMP says nothig about
 ordering it seems and as far Fortran itself goes I don't know either).
 The attached patch also contained omp statements for the metrics
 subdirectory. The only reason I did not drop them is that some of the code
 inside the if(first_call) sections was CCTK_Equals which can be quite
 expensive (if eg Exact runs at each timestep) when run for each grid point
 (or multiple times when derivatives are taken inside Exact).

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Ticket URL: <https://trac.einsteintoolkit.org/ticket/928#comment:9>
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