PetscGatherMessageLengths#

Computes information about messages that an MPI rank will receive, including (from-id,length) pairs for each message.

Synopsis#

#include "petscsys.h"  
PetscErrorCode PetscGatherMessageLengths(MPI_Comm comm, PetscMPIInt nsends, PetscMPIInt nrecvs, const PetscMPIInt ilengths[], PetscMPIInt **onodes, PetscMPIInt **olengths)

Collective

Input Parameters#

  • comm - Communicator

  • nsends - number of messages that are to be sent.

  • nrecvs - number of messages being received

  • ilengths - an array of integers of length sizeof(comm) a non zero ilengths[i] represent a message to i of length ilengths[i]

Output Parameters#

  • onodes - list of ranks from which messages are expected

  • olengths - corresponding message lengths

Notes#

With this info, the correct MPI_Irecv() can be posted with the correct from-id, with a buffer with the right amount of memory required.

The calling function deallocates the memory in onodes and olengths

To determine nrecvs, one can use PetscGatherNumberOfMessages()

See Also#

PetscGatherNumberOfMessages(), PetscGatherMessageLengths2(), PetscCommBuildTwoSided()

Level#

developer

Location#

src/sys/utils/mpimesg.c

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