C Syntax

       2003-2025, The Open MPI Community

                                                  Jun 07, 2025                                     MPI_IMRECV(3)

       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.

       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:

       • MPI_Comm_create_errhandler then MPI_Comm_set_errhandler

       • MPI_File_create_errhandler then MPI_File_set_errhandler

       • MPI_Session_create_errhandler then MPI_Session_set_errhandler or at MPI_Session_init

       • MPI_Win_create_errhandler then MPI_Win_set_errhandler

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

       See the MPImanpage for a full list of MPIerrorcodes.

       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 MPIStandard, 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.

       SEEALSO:

          • MPI_Mprobe

          • MPI_Improbe

          • MPI_Probe

          • MPI_Iprobe

          • MPI_Imrecv

          • MPI_Cancel

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

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

       • message: Message (handle).

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

       • request: Request (handle).

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

CSyntax
          #include <mpi.h>

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

   FortranSyntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_IMRECV(BUF, COUNT, DATATYPE, MESSAGE, REQUEST, IERROR)
               <type>  BUF(*)
               INTEGER COUNT, DATATYPE, MESSAGE, REQUEST, IERROR

   Fortran2008Syntax
          USE mpi_f08
          MPI_Imrecv(buf, count, datatype, message, request, ierror)
               TYPE(*), DIMENSION(..), ASYNCHRONOUS :: buf
               INTEGER, INTENT(IN) :: count
               TYPE(MPI_Datatype), INTENT(IN) :: datatype
               TYPE(MPI_Message), INTENT(INOUT) :: message
               TYPE(MPI_Request), INTENT(OUT) :: request
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror