START\_PES(3) Open MPI START\_PES(3)

shmem\_init <#shmem-init>, start\_pes - Allocates a block of memory from the symmetric heap.

# [SYNOPSIS](#SYNOPSIS)

C or C++:

```
void shmem_init(void)
void start_pes(int npes)
```

Fortran:

```
CALL SHMEM_INIT()
CALL START_PES(npes)
```

# [DESCRIPTION](#DESCRIPTION)

The start\_pes routine should be the first statement in a SHMEM parallel program.

The start\_pes routine accepts the following argument:

[**npes**](#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/enterprise-packages/openmpi-cuda-13.0/intro_shmem.3) man page.

# [EXAMPLES](#EXAMPLES)

This is a simple program that calls [shmem\_integer\_put(3)](/man/enterprise-packages/openmpi-cuda-13.0/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
```

# [NOTES](#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)](/man/enterprise-packages/openmpi-cuda-13.0/intro_shmem.3) shmem\_barrier <#shmem-barrier>(3) shmem\_barrier\_all <#shmem-barrier-all>(3) [*shmem\_put*(3)](/man/enterprise-packages/openmpi-cuda-13.0/shmem_put.3) [*my\_pe*(3)](/man/enterprise-packages/openmpi-cuda-13.0/my_pe.3) [*shmem\_n\_pes*(3)](/man/enterprise-packages/openmpi-cuda-13.0/shmem_n_pes.3)

# [Copyright](#Copyright)

2003-2026, The Open MPI Community

October 30, 2026

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Document: start_pes(3) from openmpi-cuda-13.0 5.0.11-r1 (Chainguard OS)
Source: https://github.com/open-mpi/ompi