petsc-3.3-p7 2013-05-11

PetscSFFetchAndOpBegin

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

Synopsis

PetscErrorCode PetscSFFetchAndOpBegin(PetscSF sf,MPI_Datatype unit,void *rootdata,const void *leafdata,void *leafupdate,MPI_Op op)

Collective

Input Arguments

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

Output Arguments

	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.

Examples