19.2.219. start_pes — Open MPI 5.0.1 documentation

# 19.2.219. start_pes

shmem_init, start_pes - Allocates a block of memory from the symmetric heap.

## 19.2.219.1. SYNOPSIS

C or C++:

    void shmem_init(void)
    void start_pes(int npes)

Fortran:

    CALL SHMEM_INIT()
    CALL START_PES(npes)

## 19.2.219.2. DESCRIPTION

The start_pes routine should be the first statement in a SHMEM parallel program.

The start_pes routine accepts the following argument:

npes

  Unused. Should be set to 0.

This routine initializes the SHMEM API, therefore it must be called before calling any other SHMEM routine. This routine is responsible inter alia for setting up the symmetric heap on the calling PE, and the creation of the virtual PE numbers. Upon successful return from this routine, the calling PE will be able to communicate with and transfer data to other PEs.

Multiple calls to this function are not allowed.

For an overview of programming with SHMEM communication routines, example SHMEM programs, and instructions for compiling SHMEM programs, see the intro_shmem(3) man page.

## 19.2.219.3. EXAMPLES

This is a simple program that calls shmem_integer_put(3):

    PROGRAM PUT
      INCLUDE "mpp/shmem.fh"

      INTEGER TARG, SRC, RECEIVER, BAR
      COMMON /T/ TARG
      PARAMETER (RECEIVER=1)

      CALL SHMEM_INIT()
      IF (MY_PE() .EQ. 0) THEN
        SRC = 33
        CALL SHMEM_INTEGER_PUT(TARG, SRC, 1, RECEIVER)
      ENDIF
      CALL SHMEM_BARRIER_ALL ! SYNCHRONIZES SENDER AND RECEIVER
      IF (MY_PE() .EQ. RECEIVER) THEN
        PRINT *,'PE ', MY_PE(),' TARG=',TARG,' (expect 33)'
      ENDIF
    END

## 19.2.219.4. NOTES

If the start_pes call is not the first statement in a program, unexpected results may occur on some architectures.

See also

intro_shmem(3) shmem_barrier(3) shmem_barrier_all(3) shmem_put(3) my_pe(3) shmem_n_pes(3)