SHMEM_BARRIER(3) Open MPI SHMEM_BARRIER(3)
NAME
shmem_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)
DESCRIPTION
The shmem_barrier routine does not return until the subset of PEs spec-
ified by PE_start, logPE_stride and PE_size, has entered this routine
at the same point of the execution path.
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 re-
sults.
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 in-
teger. 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 For-
tran, it must be a default integer type. Every element of this
array must be initialized to 0 before any of the PEs in the ac-
tive 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 pre-
viously issued remote memory updates done by any of the PEs in the ac-
tive 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_bar-
rier 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 repeat-
edly 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 ALSO
intro_shmem(3), shmem_barrier_all(3)
4.1.2 Nov 24, 2021 SHMEM_BARRIER(3)
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