Question

I have a FORTRAN program written for the parallel computing. The program takes the arguments and the number of threads can be defined as the argument. The sample code is as follows:

COUNT = NARGS()
      NTHREADS = 1

      ! *** GET THE COMMAND LINE ARGUMENTS, IF ANY
      IF(COUNT.GT.1)THEN
        ! *** ARGUMENT 1
        CALL GETARG(1, BUFFER, iStatus)
        IF (Buffer(1:4).EQ.'-NOP'.OR.Buffer(1:4).EQ.'-nop') THEN
          PAUSEIT=.FALSE.
        ENDIF
        IF (Buffer(1:3).EQ.'-NT'.OR.Buffer(1:3).EQ.'-nt') THEN
          READ(Buffer(4:10),*) NTHREADS
        ENDIF
        IF(COUNT.GT.2)THEN
          ! *** ARGUMENT 2
          CALL GETARG(2, BUFFER, iStatus)
          IF (Buffer(1:4).EQ.'-NOP'.OR.Buffer(1:4).EQ.'-nop') THEN
            PAUSEIT=.FALSE.
          ENDIF
          IF (Buffer(1:3).EQ.'-NT'.OR.Buffer(1:3).EQ.'-nt') THEN
            READ(Buffer(4:10),*) NTHREADS
          ENDIF
         ENDIF
      ENDIF

Let’s say my compiled file name is “hellofortran”. I can define the number of threads as

./hellofortran -nt4 

My program will read the program with 4 threads. The problem is that I can run with as many cores in any computer. Lets say I have dual core processor. I have only two cores but I can still run with 6-8 threads or any number. How can I properly define the number of threads in this particular instance ?

I hope I explained my problem. Looking forward to hearing soon on how can I improve my program. Thanks.

Jdbaba

Answer 1

If you’re using OpenMP and just looking to set up how many threads to use, I would just specify the number of threads in the environment:

OMP_NUM_THREADS=4
./hellofortran

and write your OpenMP code as you would normally. There are programmatic ways of setting thread counts but this is likely more straightforward for you.