segfault with inquire()

[Andrew Benson]

On Wednesday, December 4, 2019 2:03:41 PM PST Janne Blomqvist wrote:
> I can't immediately see what's wrong based on your stack traces, but
> in your shoes I would try to create an OpenMP testcase (forget MPI,
> that's not relevant here AFAICS) where part of the threads run INQUIRE
> and the other threads do internal IO, run it with different numbers of
> threads and see if you can recreate it.

Thanks for this suggestion. I've tried a few variations of this idea but so 
far I'm not able to reproduce the problem. Here's an example of what I've 
tried, using between 16 and 128 OpenMP threads:

program inq
  use OMP_Lib
  implicit none
  logical :: s
  character(len=27) :: c
  integer :: i, j

  i=64
  !$omp parallel private(c,j,s)
  do while (.true.)
     if (OMP_Get_Thread_Num() < omp_get_num_threads()/2) then
        open(newUnit=j,file='test.txt',form='formatted',status='unknown')
        write (c,'(e17.10)') 1.23456d0
        write (j,*) trim(c)
        close(j)
     else
        inquire(file='test.txt',exist=s)
     end if
  end do
  !$omp end parallel
end program

I compiled this with -O0 to ensure that the inquire didn't get optimized away, 
and verified that it actually calls the inquire code in libgfortran by setting 
a break point in gdb. It runs without any problems.

I'll keep trying a few other variations around this idea and see if I can 
reproduce the issue.

For what it's worth, in my code that triggers this problem I wrapped the 
"inquire()" inside an OpenMP critical section so that no more than one OpenMP 
thread can be calling inquire() at a time. So far it's been running for about 
20 hours which is the longest it's run without crashing since this problem 
began to appear. So, I take this as another piece of evidence that there's 
some thread conflict, but it doesn't really help to narrow down where it 
happens!

Thanks,
Andrew

-- 

* Andrew Benson: http://users.obs.carnegiescience.edu/abenson/contact.html

* Galacticus: https://github.com/galacticusorg/galacticus