SHMEM_BARRIER(3)SHMEM_BARRIER(3)NAMEshmem_barrier - Performs a barrier operation on a subset of processing
elements (PEs)
SYNOPSIS
C or C++:
#include <mpp/shmem.h>
void shmem_barrier(int PE_start, int logPE_stride, int PE_size,
long *pSync);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER PE_start, logPE_stride, PE_size
INTEGER pSync(SHMEM_BARRIER_SYNC_SIZE)
CALL SHMEM_BARRIER(PE_start, logPE_stride, PE_size, pSync)
DESCRIPTIONshmem_barrier is a collective synchronization routine. Control
returns from shmem_barrier after all PEs in the active set (specified
by PE_start, logPE_stride, and PE_size) have called shmem_barrier.
As with all SHMEM collective routines, each of these routines assumes
that only PEs in the active set call the routine. If a PE not in the
active set calls a SHMEM collective routine, undefined behavior
results.
The arguments are as follows:
PE_start The lowest virtual PE number of the active set of PEs.
PE_start must be of type integer. If you are using
Fortran, it must be a default integer value.
logPE_stride
The log (base 2) of the stride between consecutive virtual
PE numbers in the active set. logPE_stride must be of
type integer. If you are using Fortran, it must be a
default integer value.
PE_size The number of PEs in the active set. PE_size must be of
type integer. If you are using Fortran, it must be a
default integer value.
pSync A symmetric work array.
In C/C++, pSync must be of type int and size
_SHMEM_BARRIER_SYNC_SIZE.
In Fortran, pSync must be of type integer and size
SHMEM_BARRIER_SYNC_SIZE. If you are using Fortran, it
must be a default integer type.
Every element of this array must be initialized to 0
before any of the PEs in the active set enter
shmem_barrier the first time.
The values of arguments PE_start, logPE_stride, and PE_size must be
equal on all PEs in the active set. The same work array must be
passed in pSync to all PEs in the active set.
shmem_barrier ensures that all previously issued local stores and
previously issued remote memory updates done by any of the PEs in the
active set (by using SHMEM calls, for example shmem_put(3)) are
complete before returning.
The same pSync array may be reused on consecutive calls to
shmem_barrier if the same active PE set is used.
NOTES
The term symmetric is defined in intro_shmem(3).
If the pSync array is initialized at run time, be sure to use some
type of synchronization, for example, a call to shmem_barrier_all(3),
before calling shmem_barrier for the first time.
If the active set does not change, shmem_barrier can be called
repeatedly with the same pSync array. No additional synchronization
beyond that implied by shmem_barrier itself is necessary in this case.
EXAMPLES
C/C++ example:
shmem_barrier(PE_start, logPE_stride, size, pSync);
Fortran example:
INTEGER PSYNC(SHMEM_BARRIER_SYNC_SIZE)
INTEGER PE_START, LOGPE_STRIDE, PE_SIZE, PSYNC
DATA PSYNC /SHMEM_BARRIER_SYNC_SIZE*0/
CALL SHMEM_BARRIER(PE_START, LOGPE_STRIDE, PE_SIZE, PSYNC)
SEE ALSOintro_shmem(3), shmem_barrier_all(3)
