On 03/02/2015 22:25, Michael Black wrote:
Hi Mike and anyone else interested in the issues of multi-threaded
programming,
Below is a version of Mike's example Fortran code. I have updated it to
Fortran 90 and rather than just suggesting potential fixes, I have
actually tested the code as well ;)
I have also written it in a way that it also runs without OpemMP i.e.
single threaded by simply not passing the '-fopenmp' flag to the compiler.
For the single threaded version:
$ gfortran -o workshare1 workshare1.f90
and for the multi-threaded version:
$ gfortran -fopenmp -o workshare1_mt workshare1.f90
The source of the hang on exit is something to do with the Fortran I/O
system after it has been used from multiple threads. Possibly a defect
but by simply writing something to the console after all the threads are
joined, the program no longer intermittently hangs on exit.
+++++++++++++++++++++++++++++++++++++++++++
program workshare1
implicit none
!$ interface
!$ integer function omp_get_num_threads ()
!$ end function
!$ integer function omp_get_thread_num ()
!$ end function
!$ end interface
!$ integer :: tid, CHUNKSIZE, chunk
integer :: N, i
parameter (N=100)
!$ parameter (CHUNKSIZE=10)
real, dimension (N) :: a, b, c
! Some initializations
do i = 1, N
a(i) = i * 1.0
b(i) = a(I)
end do
!$ chunk = CHUNKSIZE
!$omp parallel shared(a,b,c) private(i,tid)
!$ tid = omp_get_thread_num ()
!$omp critical(io)
!$ if (tid .eq. 0) then
!$ print *, 'Number of threads =', omp_get_num_threads ()
!$ end if
!$ print *, 'Thread', tid, ' starting...'
!$omp end critical(io)
!$omp do schedule(dynamic,chunk)
do i = 1, N
c(i) = a(i) + b(i)
!$omp critical(io)
!$ write(*,100,advance='no') tid
write(*,101) i, c(i)
!$omp end critical(io)
100 format(' Thread', i2, ':')
101 format(' C(', i3,')=', F8.2)
end do
!$omp end do nowait
!$omp critical(io)
!$ print *, 'Thread', tid, ' done.'
!$omp end critical(io)
!$omp end parallel
print *, 'All done'
end program workshare1
-------------------------------------------------------
73
Bill
G4WJS.
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