FLUSH Directive

!$OMP FLUSH [(list)]

The binding thread set for a FLUSH construct is the encountering thread.

The FLUSH directive must appear at the precise point in the code at which the synchronization is required. To avoid flushing all variables, specify a list.

Thread-visible variables are written back to memory at the point at which this directive appears. Modifications to thread-visible variables are visible to all threads after this point. Subsequent reads of thread-visible variables fetch the latest copy of the data.

Thread-visible variables include the following data items:

• Globally visible variables (common blocks and modules)

• Local variables that do not have the SAVE attribute but have had their address taken and saved or have had their address passed to another subprogram

• Local variables that do not have the SAVE attribute that are declared shared in a parallel region within the subprogram

• Dummy arguments

• All pointer dereferences

The FLUSH directive is implied for the following directives (unless the NOWAIT keyword is used):

• ATOMIC and END ATOMIC

• BARRIER

• CRITICAL and END CRITICAL

• END DO

• END PARALLEL

• END SECTIONS

• END SINGLE

• END WORKSHARE

• ORDERED and END ORDERED

• PARALLEL and END PARALLEL

• PARALLEL DO and END PARALLEL DO

• PARALLEL SECTIONS and END PARALLEL SECTIONS

• TARGET

• TARGET DATA

• TARGET ENTER DATA on entry

• TARGET EXIT DATA on exit

• TARGET UPDATE on entry if TO is present and on exit if FROM is present

Example

The following example uses the FLUSH directive for point-to-point synchronization between pairs of threads:

  !$OMP PARALLEL DEFAULT(PRIVATE) SHARED(ISYNC)
        IAM = OMP_GET_THREAD_NUM( )
        ISYNC(IAM) = 0
  !$OMP BARRIER
        CALL WORK( )
  C I AM DONE WITH MY WORK, SYNCHRONIZE WITH MY NEIGHBOR
        ISYNC(IAM) = 1
  !$OMP FLUSH(ISYNC)
  C WAIT TILL NEIGHBOR IS DONE
        DO WHILE (ISYNC(NEIGH) .EQ. 0)
  !$OMP FLUSH(ISYNC)
        END DO
  !$OMP END PARALLEL