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  and  MPI_Iprobe, the MPI_Mprobe and MPI_Improbe operations allow incoming messages to be
       queried without actually receiving them, except that 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  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 or 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_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 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.

       SEE ALSO:

          • MPI_Mprobe

          • MPI_Probe

          • MPI_Iprobe

          • MPI_Mrecv

          • MPI_Imrecv

          • MPI_Cancel

COPYRIGHT

       2003-2025, The Open MPI Community

                                                  Feb 17, 2025                                    MPI_IMPROBE(3)