MPI_Intercomm_create

--- Creates an intercommuncator from two intracommunicators

Input Paramters

local_comm: Local (intra)communicator

local_leader: Rank in local_comm of leader (often 0)

peer_comm: Remote (intra)communicator

remote_leader: Rank in peer_comm of leader (often 0)

tag: Message tag to use in constructing intercommunicator; if multiple

MPI_Intercomm_creates are being made, they should use different tags (more precisely, ensure that the local and remote leaders are using different tags for each MPI_intercomm_create).

Output Parameter

comm_out: Created intercommunicator

int MPI_Intercomm_create ( local_comm, local_leader, peer_comm, remote_leader, tag, comm_out )

Algorithm

1): Allocate a send context, an inter-coll context, and an intra-coll context

2): Send "send_context" and lrank_to_grank list from local comm group if I'm the local_leader.

3): If I'm the local leader, then wait on the posted sends and receives to complete. Post the receive for the remote group information and wait for it to complete.

4): Broadcast information received from the remote leader.

5): Create the inter_communicator from the information we now have.

An: inter-communicator ends up with three levels of communicators. The inter-communicator returned to the user, a "collective" inter-communicator that can be used for safe communications between local ∧ remote groups, and a collective intra-communicator that can be used to allocate new contexts during the merge and dup operations.

For the resulting inter-communicator, comm_out

comm_out = inter-communicator comm_out->comm_coll = "collective" inter-communicator comm_out->comm_coll->comm_coll = safe collective intra-communicator

Synopsis


#include "mpi.h"
int MPI_Intercomm_create ( local_comm, local_leader, peer_comm, 
                           remote_leader, tag, comm_out )
MPI_Comm  local_comm;
int       local_leader;
MPI_Comm  peer_comm;
int       remote_leader;
int       tag;
MPI_Comm *comm_out;

Location: ic_create.c