Nonblocking communication

Nonblocking communications use methods of the Request class to identify communication operations and match the operation that initiates the communication with the operation that terminates it.

Request Comm.Isend(Object buf, int offset, int count,
                   Datatype datatype, int dest, int tag)

buf	send buffer array
offset	initial offset in send buffer
count	number of items to send
datatype	datatype of each item in send buffer
dest	rank of destination
tag	message tag
returns:	communication request

Start a standard mode, nonblocking send. Java binding of the MPI operation MPI_ISEND. Further comments as for send.

Request Comm.Ibsend(Object buf, int offset, int count,
                    Datatype datatype, int dest, int tag)

buf	send buffer array
offset	initial offset in send buffer
count	number of items to send
datatype	datatype of each item in send buffer
dest	rank of destination
tag	message tag
returns:	communication request

Start a buffered mode, nonblocking send. Java binding of the MPI operation MPI_IBSEND. Further comments as for send.

Request Comm.Issend(Object buf, int offset, int count,
                    Datatype datatype, int dest, int tag)

buf	send buffer array
offset	initial offset in send buffer
count	number of items to send
datatype	datatype of each item in send buffer
dest	rank of destination
tag	message tag
returns:	communication request

Start a synchronous mode, nonblocking send. Java binding of the MPI operation MPI_ISSEND. Further comments as for send.

Request Comm.Irsend(Object buf, int offset, int count,
                    Datatype datatype, int dest, int tag)

buf	send buffer array
offset	initial offset in send buffer
count	number of items to send
datatype	datatype of each item in send buffer
dest	rank of destination
tag	message tag
returns:	communication request

Start a ready mode, nonblocking send. Java binding of the MPI operation MPI_IRSEND. Further comments as for send.

Request Comm.Irecv(Object buf, int offset, int count,
                   Datatype datatype, int source, int tag)

buf	receive buffer array
offset	initial offset in receive buffer
count	number of items in receive buffer
datatype	datatype of each item in receive buffer
source	rank of source
tag	message tag
returns:	communication request

Start a nonblocking receive. Java binding of the MPI operation MPI_IRECV. Further comments as for recv.

The following functions are used to complete nonblocking communication operations (and also communications started using the persistent communication requests--subclass Prequest--introduced later). We use the following terminology. A request is ``active'' if it is associated with an ongoing communication. Otherwise it is inactive. An inactive instance of the base class Request is called a ``void request''. (Note, however, that an inactive instance of the Prequest subclass is not said to be ``void'', because it retains detailed information about a communication pattern even when no corresponding communication is ongoing.)

• Rationale. A ``void request'' corresponds to what is called a ``null handle'' in the C and Fortran MPI bindings. It seems impractical to have completion operations like wait set request object references to null references in the Java sense (because Java methods cannot directly modify references passed to them as arguments). To avoid a confusing semantic distinction between null MPI handles and null Java references we introduce the terminology of a ``void request object''. If an explicit reference to a void request is needed, one is available as MPI.REQUEST_NULL. The inquiry Request.Is_null can be used to determine if a particular request is void.(End of rationale.)

Status Request.Wait()

returns:

status object

Blocks until the operation identified by the request is complete. Java binding of the MPI operation MPI_WAIT. After the call returns, the request object becomes inactive.

Status Request.Test()

returns:

status object or null reference

Returns a status object if the operation identified by the request is complete, or a null reference otherwise. Java binding of the MPI operation MPI_TEST. After the call, if the operation is complete (ie, if the return value of test is non-null), the request object becomes an inactive request.

boolean Request.Is_null()

returns:

true if the request object is void, false otherwise

Note that Is_null is always false on instances of the subclass Prequest.

void Request.Free()

Set the request object to be void. Java binding of the MPI operation MPI_REQUEST_FREE.

static Status Request.Waitany(Request [] array_of_requests)

array_of_requests	array of requests
returns:	status object

Blocks until one of the operations associated with the active requests in the array has completed. Java binding of the MPI operation MPI_WAITANY. The index in array_of_requests for the request that completed can be obtained from the status object from the publically accessible Status.index field. The corresponding element of array_of_requests becomes inactive.

The array_of_requests may contain inactive requests. If the list contains no active requests, the method immediately returns a status in which the index field is MPI.UNDEFINED.

static Status Request.Testany(Request [] array_of_requests)

array_of_requests	array of requests
returns:	status object or null reference

Tests for completion of either one or none of the operations associated with active requests. Java binding of the MPI operation MPI_TESTANY. If some request completed, the index in array_of_requests of that request can be obtained from the status object through the Status.index field. The corresponding element of array_of_requests becomes inactive. If no request completed, testAny returns a null reference.

The array_of_requests may contain inactive requests. If the list contains no active requests, the method immediately returns a status in which the index field is MPI.UNDEFINED.

static Status [] Request.Waitall(Request [] array_of_requests)

array_of_requests	array of requests
returns:	array of status objects

Blocks until all of the operations associated with the active requests in the array have completed. Java binding of the MPI operation MPI_WAITALL. The result array will be the same size as array_of_requests. On exit, requests become inactive. If the input value of array_of_requests contains any inactive requests, corresponding elements of the result array will contain null status references.

static Status [] Request.Testall(Request [] array_of_requests)

array_of_requests	array of requests
returns:	array of status objects, or a null reference

Tests for completion of all of the operations associated with active requests. Java binding of the MPI operation MPI_TESTALL. If all operations have completed, the exit values of the argument array and the result array are as for Waitall. If any operation has not completed, the result value is null and no element of the argument array is modified.

static Status [] Request.Waitsome(Request [] array_of_requests)

array_of_requests	array of requests
returns:	array of status objects

Blocks until at least one of the operations associated with the active requests in the array has completed. Java binding of the MPI operation MPI_WAITSOME. The size of the result array will be the number of operations that completed. The index in array_of_requests for each request that completed can be obtained from the index field of the returned status objects. The corresponding elements in array_of_requests become inactive.

If array_of_requests list contains no active requests, testAll immediately returns a null reference.

static Status [] Request.Testsome(Request [] array_of_requests)

array_of_requests	array of requests
returns:	array of status objects

Behaves like waitSome, except that it returns immediately. Java binding of the MPI operation MPI_TESTSOME. If no operation has completed, Testsome returns an array of length zero and elements of array_of_requests are unchanged. Otherwise, arguments and return value are as for Waitsome.