[petsc-users] Petsc messing with OpenMP

Timothée Nicolas timothee.nicolas at gmail.com
Tue Jan 30 10:57:30 CST 2018

Dear petsc team,

For a while, I have been wondering why I have never managed to print what
threads are doing in an openMP region in my FORTRAN programs. Some people
told me it was normal because threads will get confused all trying to write
at the same time. However I realised today that the problem seems to be
related to petsc. I have a super simple "hello world" example that
reproduces the problem :

program hello

  !$ use omp_lib

  implicit none

  integer nthreads, tid

  !$omp parallel private(nthreads, tid)

  tid = omp_get_thread_num()

  print *, 'hello world from thread = ', tid

  if (tid .eq. 0) then

     nthreads = omp_get_num_threads()

     print *, 'number of threads = ', nthreads

  end if

  !$omp end parallel

end program hello

If I compile it with

mpif90 -qopenmp -o omp main.f90

Then I get no problem. But if I link petsc library (as is the case in my
code) :

mpif90 -qopenmp -o omp main.f90
-L/home/timotheenicolas/petsc-3.7.3/arch-linux2-c-debug/lib -lpetsc

Then I get the following error after execution of export

 hello world from thread =            0

 number of threads =            2

forrtl: severe (40): recursive I/O operation, unit -1, file unknown

Image              PC                Routine            Line        Source

omp                0000000000403BC8  Unknown               Unknown  Unknown

omp                0000000000403572  Unknown               Unknown  Unknown

libiomp5.so        00002AAAAD3146A3  Unknown               Unknown  Unknown

libiomp5.so        00002AAAAD2E3007  Unknown               Unknown  Unknown

libiomp5.so        00002AAAAD2E26F5  Unknown               Unknown  Unknown

libiomp5.so        00002AAAAD3149C3  Unknown               Unknown  Unknown

libpthread.so.0    00002AAAAD5BADC5  Unknown               Unknown  Unknown

libc.so.6          00002AAAAD8C5CED  Unknown               Unknown  Unknown

This means that in my programs using petsc, I can't use prints to see
exactly what the threads are doing, which is a pain when debug is required
(that is to say, all the time). Is this issue expected ?

Thx in advance

Timothee NICOLAS
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