PetscSFFetchAndOpBegin#

begin operation that fetches values from root and updates atomically by applying operation using my leaf value, to be completed with PetscSFFetchAndOpEnd()

Synopsis#

#include "petscsf.h" 
PetscErrorCode PetscSFFetchAndOpBegin(PetscSF sf, MPI_Datatype unit, void *rootdata, const void *leafdata, void *leafupdate, MPI_Op op)

Collective

Input Parameters#

sf - star forest
unit - data type
leafdata - leaf values to use in reduction
op - operation to use for reduction

Output Parameters#

rootdata - root values to be updated, input state is seen by first process to perform an update
leafupdate - state at each leaf’s respective root immediately prior to my atomic update

Note#

The update is only atomic at the granularity provided by the hardware. Different roots referenced by the same process might be updated in a different order. Furthermore, if a composite type is used for the unit datatype, atomicity is not guaranteed across the whole vertex. Therefore, this function is mostly only used with primitive types such as integers.