MPI_IMPROBE(3)					     Open MPI					    MPI_IMPROBE(3)

MPI_Improbe — Non-blocking matched probe for a message.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Improbe(int source, int tag, MPI_Comm comm,
	       int *flag, MPI_Message *message, MPI_Status *status)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_IMPROBE(SOURCE, TAG, COMM, FLAG, MESSAGE, STATUS, IERROR)
	       LOGICAL FLAG
	       INTEGER SOURCE, TAG, COMM, MESSAGE
	       INTEGER STATUS(MPI_STATUS_SIZE), IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Improbe(source, tag, comm, flag, message, status, ierror)
	       INTEGER, INTENT(IN) :: source, tag
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       INTEGER, INTENT(OUT) :: flag
	       TYPE(MPI_Message), INTENT(OUT) :: message
	       TYPE(MPI_Status) :: status
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETERS
       • source: Source rank or MPI_ANY_SOURCE (integer).

       • tag: Tag value or MPI_ANY_TAG (integer).

       • comm: Communicator (handle).

OUTPUT PARAMETERS
       • flag: Flag (logical).

       • message: Message (handle).

       • status: Status object (status).

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

DESCRIPTION
       Like  MPI_Probe	<#mpi-probe>  and  MPI_Iprobe  <#mpi-iprobe>, the MPI_Mprobe <#mpi-mprobe> and MPI_Improbe
       operations allow incoming messages to be queried without actually receiving them, except that MPI_Mprobe <#
       mpi-mprobe> and MPI_Improbe provide a mechanism to receive the specific message that was matched regardless
       of other intervening probe or receive operations. This gives the application an opportunity to  decide  how
       to  receive the message, based on the information returned by the probe. In particular, the application may
       allocate memory for the receive buffer according to the length of the probed message.

       A matching probe with MPI_PROC_NULL as source returns flag = true,

       message = MPI_MESSAGE_NO_PROC, and the status object returns source ^ MPI_PROC_NULL, tag ^ MPI_ANY_TAG, and
       count ^ 0.

       MPI_Iprobe <#mpi-iprobe> returns a true value in flag if a message has been matched and can be received	by
       passing	the  message  handle to the MPI_Mrecv <#mpi-mrecv> or MPI_Imrecv <#mpi-imrecv> functions, provided
       the source was not MPI_PROC_NULL.

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.

       See also:

	  • MPI_Mprobe <#mpi-mprobe>

	  • MPI_Probe <#mpi-probe>

	  • MPI_Iprobe <#mpi-iprobe>

	  • MPI_Mrecv <#mpi-mrecv>

	  • MPI_Imrecv <#mpi-imrecv>

	  • MPI_Cancel <#mpi-cancel>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					    MPI_IMPROBE(3)
