START_PES(3)START_PES(3)


NAME
     start_pes - Called at the beginning of a SHMEM program to identify the
     number of processes desired

SYNOPSIS
     C or C++:

        void start_pes(int npes);

     Fortran:

        CALL START_PES(npes)

DESCRIPTION
     The start_pes routine identifies the number of processes for a
     program.  This statement must be the first statement in a program that
     uses distributed, shared memory (SHMEM) communication routines.  The
     start_pes routine accepts the following argument:

     npes      Identifies the total number of processing elements (PEs)
               desired.  If npes is 0, the number of PEs is selected by the
               NPES environment variable.  The type of NPES is default
               integer.

     If your parallel application uses MPI and SHMEM, you can omit the
     start_pes call and call MPI_Init and MPI_Finalize, as specified in the
     MPI standard, and launch the program with the mpirun command.  Do not
     call both MPI_init and start_pes from the same program.

     Programs that use both SHMEM and MPI must call MPI_Init and
     MPI_Finalize instead of start_pes.  PVM and SHMEM communication cannot
     be used in the same program.

     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.

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

        PROGRAM PUT

        INTEGER TARG, SRC, RECEIVER, BAR
        COMMON /T/ TARG
        PARAMETER (RECEIVER=1)
        CALL START_PES(0)

        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
                CALL SHMEM_UDCFLUSH()    ! NOT REQUIRED ON IRIX SYSTEMS
                PRINT*,'PE ', MY_PE(),' TARG=',TARG
                IF (TARG.NE.33) PRINT*,'FAIL'
        ENDIF
        END

NOTES
     If the start_pes call is not the first statement in a program,
     unexpected results will occur.  Static data areas initialized prior to
     the start_pes call will sometimes be set to zero during start_pes
     processing.

SEE ALSO
     fork(2)

     intro_shmem(3), shmem_barrier(3), shmem_barrier_all(3), shmem_put(3)

     my_pe(3I), num_pes(3I)

     Message Passing Toolkit: MPI Programmer's Manual