MPI_IMRECV(3)					     Open MPI					     MPI_IMRECV(3)

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
	  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

   Fortran 2008 Syntax
	  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

INPUT PARAMETERS
       • 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 <#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 <#mpi-test> and MPI_Wait <#
       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	<#
       mpi-test>  or  MPI_Wait <#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  <#mpi-cancel>. If MPI_Cancel <#mpi-cancel> succeeds, the matched message must be
       found by a subsequent message  probe  (MPI_Probe	 <#mpi-probe>,	MPI_Iprobe  <#mpi-iprobe>,  MPI_Mprobe	<#
       mpi-mprobe>,  or MPI_Improbe <#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>/MPI_Init_thread <#mpi-init-thread>,
       after MPI_Finalize <#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 <#
       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>/MPI_Comm_spawn_multiple	<#
       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 <#mpi-abort> was called on that communicator. If called
	 on  a window or file, acts as if MPI_Abort <#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	<#mpi-comm-create-errhandler>	  then	   MPI_Comm_set_errhandler	<#
	 mpi-comm-set-errhandler>

       • MPI_File_create_errhandler	 <#mpi-file-create-errhandler>	   then	    MPI_File_set_errhandler	<#
	 mpi-file-set-errhandler>

       • MPI_Session_create_errhandler	 <#mpi-session-create-errhandler>   then   MPI_Session_set_errhandler	<#
	 mpi-session-set-errhandler> or at MPI_Session_init <#mpi-session-init>

       • MPI_Win_create_errhandler	<#mpi-win-create-errhandler>	  then	    MPI_Win_set_errhandler	<#
	 mpi-win-set-errhandler>

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

       See the MPI man page <#open-mpi> for a full list of MPI error codes <#open-mpi-errors>.

       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
       <https://www.mpi-forum.org/docs/>,  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.

       See also:

	  • MPI_Mprobe <#mpi-mprobe>

	  • MPI_Improbe <#mpi-improbe>

	  • MPI_Probe <#mpi-probe>

	  • MPI_Iprobe <#mpi-iprobe>

	  • MPI_Imrecv

	  • MPI_Cancel <#mpi-cancel>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					     MPI_IMRECV(3)
