# 18.2.134. shmem_long_wait

shmem_int_wait(3), shmem_int_wait(3)_until, shmem_int4_wait(3), shmem_int4_wait(3)_until, shmem_int8_wait(3), shmem_int8_wait(3)_until, shmem_long_wait(3), shmem_long_wait(3)_until, shmem_longlong_wait(3), shmem_longlong_wait(3)_until, shmem_short_wait(3), shmem_short_wait(3)_until, shmem_wait(3), shmem_wait(3)_until - Waits for a variable on the local processing element (PE) to change

## 18.2.134.1. SYNOPSIS

C or C++:

    #include <mpp/shmem.h>

    void shmem_int_wait(volatile int *var, int value)

    void shmem_int_wait_until(volatile int *var, int cond, int value)

    void shmem_long_wait(volatile long *var, long value)

    void shmem_long_wait_until(volatile long *var, int cond, long value)

    void shmem_longlong_wait(volatile long long *var, long long value)

    void shmem_longlong_wait_until(volatile long long *var, int cond,
      long long value)

    void shmem_short_wait(volatile short *var, short value)

    void shmem_short_wait_until(volatile short *var, int cond,
      short value)

    void shmem_wait(volatile long *ivar, long cmp_value)

    void shmem_wait_until(volatile 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)

## 18.2.134.2. 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.

## 18.2.134.3. 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

See also

intro_shmem(3) shmem_put(3)