mpi.send: MPI_Send, MPI_Isend, MPI_Recv, and MPI_Irecv APIs

Description

The pair mpi.send and mpi.recv are two most used blocking calls for point-to-point communications. An int, double or char vector can be transmitted from any source to any destination.

The pair mpi.isend and mpi.irecv are the same except that they are nonblocking calls.

Blocking and nonblocking calls are interchangeable, e.g., nonblocking sends can be matched with blocking receives, and vice-versa.

Usage

mpi.send(x, type, dest, tag,  comm = 1)
mpi.isend(x, type, dest, tag,  comm = 1, request=0)
mpi.recv(x, type, source, tag,  comm = 1, status = 0)
mpi.irecv(x, type, source, tag,  comm = 1, request = 0)

Value

mpi.send and mpi.isend return no value. mpi.recv

returns the int, double or char vector sent from source. However, mpi.irecv returns no value. See details for explanation.

Arguments

x: data to be sent or received. Must be the same type for source and destination. The receive buffer must be as large as the send buffer.
type: 1 for integer, 2 for double, and 3 for character. Others are not supported.
dest: the destination rank. Use mpi.proc.null for a fake destination.
source: the source rank. Use mpi.any.source for any source. Use mpi.proc.null for a fake source.
tag: non-negative integer. Use mpi.any.tag for any tag flag.
comm: a communicator number.
request: a request number.
status: a status number.

Author

Hao Yu

Details

The pair mpi.send (or mpi.isend) and mpi.recv (or mpi.irecv) must be used together, i.e., if there is a sender, then there must be a receiver. Any mismatch will result a deadlock situation, i.e., programs stop responding. The receive buffer must be large enough to contain an incoming message otherwise programs will be crashed. One can use mpi.probe (or mpi.iprobe) and mpi.get.count to find the length of an incoming message before calling mpi.recv. If mpi.any.source or mpi.any.tag is used in mpi.recv, one can use mpi.get.sourcetag to find out the source or tag of the received message. To send/receive an R object rather than an int, double or char vector, please use the pair mpi.send.Robj and mpi.recv.Robj.

Since mpi.irecv is a nonblocking call, x with enough buffer must be created before using it. Then use nonblocking completion calls such as mpi.wait or mpi.test to test if x contains data from sender.

If multiple nonblocking sends or receives are used, please use request number consecutively from 0. For example, to receive two messages from two slaves, try mpi.irecv(x,1,source=1,tag=0,comm=1,request=0) mpi.irecv(y,1,source=2,tag=0,comm=1,request=1) Then mpi.waitany, mpi.waitsome or mpi.waitall can be used to complete the operations.

References

https://www.open-mpi.org/

Examples

Run this code

# \donttest{
#on a slave
#mpi.send(1:10,1,0,0)

#on master
#x <- integer(10)
#mpi.irecv(x,1,1,0)
#x	
#mpi.wait()
#x
# }

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