17.2.211. MPI_Imrecv

MPI_Imrecv — Non-blocking receive for a matched message SYNTAX C Syntax

#include <mpi.h>

int MPI_Imrecv(void *buf, int count, MPI_Datatype type,
     MPI_Message *message, MPI_Request *request) Fortran Syntax

! or the older form: INCLUDE 'mpif.h'
     <type>  BUF(*)

USE mpi_f08
MPI_Imrecv(buf, count, datatype, message, request, ierror)
     INTEGER, INTENT(IN) :: count
     TYPE(MPI_Datatype), INTENT(IN) :: datatype
     TYPE(MPI_Message), INTENT(INOUT) :: message
     TYPE(MPI_Request), INTENT(OUT) :: request

  • count: Number of elements to receive (nonnegative integer).

  • datatype: Datatype of each send buffer element (handle).

  • message: Message (handle). OUTPUT PARAMETERS

  • buf: Initial address of receive buffer (choice).

  • request: Request (handle).

  • ierror: Fortran only: Error status (integer). DESCRIPTION

The functions MPI_Mrecv and MPI_Imrecv receive messages that have been previously matched by a matching probe.

The request returned from MPI_Imrecv can be used with any of the MPI_Test and MPI_Wait variants, like any non-blocking receive request.

If MPI_Imrecv is called with MPI_MESSAGE_NULL as the message argument, a call to one of the MPI_Test or MPI_Wait variants will return immediately with the status object set to source = MPI_PROC_NULL, tag = MPI_ANY_TAG, and count = 0, as if a receive from MPI_PROC_NULL was issued.

If reception of a matched message is started with MPI_Imrecv, then it is possible to cancel the returned request with MPI_Cancel. If MPI_Cancel succeeds, the matched message must be found by a subsequent message probe (MPI_Probe, MPI_Iprobe, MPI_Mprobe, or MPI_Improbe), received by a subsequent receive operation or canceled by the sender.

Note, however, that is it possible for the cancellation of operations initiated with MPI_Imrecv to fail. An example of a failing case is when canceling the matched message receive would violate MPI message ordering rules (e.g., if another message matching the same message signature has matched — and possibly received — before this MPI_Imrecv is canceled).

If your application does not need to examine the status field, you can save resources by using the predefined constant MPI_STATUS_IGNORE as a special value for the status argument. ERRORS

Almost all MPI routines return an error value; C routines as the return result of the function and Fortran routines in the last argument.

Before the error value is returned, the current MPI error handler associated with the communication object (e.g., communicator, window, file) is called. If no communication object is associated with the MPI call, then the call is considered attached to MPI_COMM_SELF and will call the associated MPI error handler. When MPI_COMM_SELF is not initialized (i.e., before MPI_Init/MPI_Init_thread, after MPI_Finalize, or when using the Sessions Model exclusively) the error raises the initial error handler. The initial error handler can be changed by calling MPI_Comm_set_errhandler on MPI_COMM_SELF when using the World model, or the mpi_initial_errhandler CLI argument to mpiexec or info key to MPI_Comm_spawn/MPI_Comm_spawn_multiple. If no other appropriate error handler has been set, then the MPI_ERRORS_RETURN error handler is called for MPI I/O functions and the MPI_ERRORS_ABORT error handler is called for all other MPI functions.

Open MPI includes three predefined error handlers that can be used:

  • MPI_ERRORS_ARE_FATAL Causes the program to abort all connected MPI processes.

  • MPI_ERRORS_ABORT An error handler that can be invoked on a communicator, window, file, or session. When called on a communicator, it acts as if MPI_Abort was called on that communicator. If called on a window or file, acts as if MPI_Abort was called on a communicator containing the group of processes in the corresponding window or file. If called on a session, aborts only the local process.

  • MPI_ERRORS_RETURN Returns an error code to the application.

MPI applications can also implement their own error handlers by calling:

Note that MPI does not guarantee that an MPI program can continue past an error.

See the MPI man page for a full list of MPI error codes.

See the Error Handling section of the MPI-3.1 standard for more information.

Note that per the “Return Status” section in the “Point-to-Point Communication” chapter in the MPI Standard, MPI errors on messages received by MPI_Imrecv do not set the status.MPI_ERROR field in the returned status. The error code is always passed to the back-end error handler and may be passed back to the caller through the return value of MPI_Imrecv if the back-end error handler returns it. The pre-defined MPI error handler MPI_ERRORS_RETURN exhibits this behavior, for example.