SYNOPSIS

C or C++:

#include <mpp/shmem.h>
void shmem_int_wait(int *var, int value);
void shmem_int_wait_until(int *var, int cond, int value);
void shmem_long_wait(long *var, long value);
void shmem_long_wait_until(long *var, int cond, long value);
void shmem_longlong_wait(long long *var, long long value);
void shmem_longlong_wait_until(long long *var, int cond,
long long value);
void shmem_short_wait(short *var, short value);
void shmem_short_wait_until(short *var, int cond,
short value);
void shmem_wait(long *ivar, long cmp_value);
void shmem_wait_until(long *ivar, int cmp, long value);

Fortran:

INCLUDE "mpp/shmem.fh"
CALL SHMEM_INT4_WAIT(ivar, cmp_value)
CALL SHMEM_INT4_WAIT_UNTIL(ivar, cmp, cmp_value)
CALL SHMEM_INT8_WAIT(ivar, cmp_value)
CALL SHMEM_INT8_WAIT_UNTIL(ivar, cmp, cmp_value)
CALL SHMEM_WAIT(ivar, cmp_value)
CALL SHMEM_WAIT_UNTIL(ivar, cmp, cmp_value)

DESCRIPTION

shmem_wait and shmem_wait_until wait for ivar to be changed by a remote write or atomic swap issued by a different processor. These routines can be used for point-to- point directed synchronization. A call to shmem_wait does not return until some other processor writes a value, not equal to cmp_value, into ivar on the waiting processor. A call to shmem_wait_until does not return until some other processor changes ivar to satisfy the condition implied by cmp and cmp_value. This mechanism is useful when a processor needs to tell another processor that it has completed some action.

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.

ivar

A remotely accessible integer variable that is being updated by another PE. If you are using C/C++, the type of ivar should match that implied in the SYNOPSIS section. If you are using Fortran, ivar must be a specific sized integer type according to the function being called, as follows:

shmem_wait, shmem_wait_until: default INTEGER

shmem_int4_wait, shmem_int4_wait_until: INTEGER*4

shmem_int8_wait, shmem_int8_wait_until: INTEGER*8

cmp

The compare operator that compares ivar with cmp_value. cmp must be of type integer. If you are using Fortran, it must be of default kind. If you are using C/C++, the type of cmp should match that implied in the SYNOPSIS section. The following cmp values are supported:

SHMEM_CMP_EQ

Equal

SHMEM_CMP_NE

Not equal

SHMEM_CMP_GT

Greater than

SHMEM_CMP_LE

Less than or equal to

SHMEM_CMP_LT

Less than

SHMEM_CMP_GE

Greater than or equal to

cmp_value

cmp_value must be of type integer. If you are using C/C++, the type of cmp_value should match thatimplied in the SYNOPSIS section. If you are using Fortran, cmp_value must be an integer of the same size and kind as ivar. The shmem_wait routines return when ivar is no longer equal to cmp_value. The shmem_wait_until routines return when the compare condition is true. The compare condition is defined by the ivar argument compared with the cmp_value using the comparison operator, cmp.

EXAMPLES

Example 1: The following call returns when variable ivar is not equal to 100:

INTEGER*8 IVAR
CALL SHMEM_INT8_WAIT(IVAR, INT8(100))

Example 2: The following call to SHMEM_INT8_WAIT_UNTIL is equivalent to the call to SHMEM_INT8_WAIT in example 1:

INTEGER*8 IVAR
CALL SHMEM_INT8_WAIT_UNTIL(IVAR, SHMEM_CMP_NE, INT8(100))

Example 3: The following C/C++ call waits until the sign bit in ivar is set by a transfer from a remote PE:

int ivar;
shmem_int_wait_until(&ivar, SHMEM_CMP_LT, 0);

Example 4: The following Fortran example is in the context of a subroutine:

SUBROUTINE EXAMPLE()
  INTEGER FLAG_VAR
  COMMON/FLAG/FLAG_VAR
  . . .
  FLAG_VAR = FLAG_VALUE ! initialize the event variable
  . . .
  IF (FLAG_VAR .EQ. FLAG_VALUE) THEN
    CALL SHMEM_WAIT(FLAG_VAR, FLAG_VALUE)
  ENDIF
  FLAG_VAR = FLAG_VALUE ! reset the event variable for next time
  . . .
END