NAME¶
shmem_int_cswap(3), shmem_int4_cswap(3),
shmem_int8_cswap(3), shmem_long_cswap(3),
shmem_longlong_cswap(3) - Performs an atomic conditional swap to a
remote data object
SYNOPSIS¶
C or C++:
#include <mpp/shmem.h>
int shmem_int_cswap(int *target, int cond, int value, int pe);
long shmem_long_cswap(long *target, long cond, long value,
int pe);
long long shmem_longlong_cswap(longlong *target,
longlong cond, longlong value, int pe);
Fortran:
INCLUDE "mpp/shmem.fh"
INTEGER pe
INTEGER(KIND=4) SHMEM_INT4_CSWAP
ires = SHMEM_INT4_CSWAP(target, cond, value, pe)
INTEGER(KIND=8) SHMEM_INT8_CSWAP
ires = SHMEM_INT8_CSWAP(target, cond, value, pe)
DESCRIPTION¶
The conditional swap routines conditionally update a target data object on an
arbitrary processing element (PE) and return the prior contents of the data
object in one atomic operation.
The arguments are as follows:
- target
- The remotely accessible integer data object to be updated on the remote
PE. If you are using C/C++, the type of target should match that implied
in the SYNOPSIS section. If you are using the Fortran compiler, it must be
of type integer with an element size of 4 bytes for SHMEM_INT4_ADD and 8
bytes for SHMEM_INT8_ADD.
- value
- The value to be atomically added to target. If you are using C/C++, the
type of value should match that implied in the SYNOPSIS section. If you
are using Fortran, it must be of type integer with an element size of
target.
- pe
- An integer that indicates the PE number upon which target is to be
updated. If you are using Fortran, it must be a default integer
value.
- target
- The remotely accessible integer data object to be updated on the remote
PE. If you are using C/C++, the data type of target should match that
implied in the SYNOPSIS section. If you are using Fortran, it must be of
the following type:
- SHMEM_INT4_CSWAP: 4-byte integer
- SHMEM_INT8_CSWAP: 8-byte integer
- cond
- cond is compared to the remote target value. If cond and the remote target
are equal, then value is swapped into the remote target. Otherwise, the
remote target is unchanged. In either case, the old value of the remote
target is returned as the function return value. cond must be of the same
data type as target.
- value
- The value to be atomically written to the remote PE. value must be the
same data type as target.
- pe
- An integer that indicates the PE number upon which target is to be
updated. If you are using Fortran, it must be a default integer
value.
NOTES¶
The term remotely accessible is defined in intro_shmem(3).
RETURN VALUES¶
The contents that had been in the target data object on the remote PE prior to
the conditional swap.
EXAMPLES¶
The following call ensures that the first PE to execute the conditional swap
will successfully write its PE number to race_winner on PE 0.
main()
{
static int race_winner = -1;
int oldval;
shmem_init();
oldval = shmem_int_cswap(&race_winner, -1, shmem_my_pe(), 0);
if (oldval == -1)
printf("pe %d was first\n",shmem_my_pe());
}
SEE ALSO¶
intro_shmem(3), shmem_cache(3), shmem_swap(3)