# 17.2.256. MPI_Mprobe

MPI_Mprobe — Blocking matched probe for a message.

## 17.2.256.1. SYNTAX

### 17.2.256.1.1. C Syntax

    #include <mpi.h>

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

### 17.2.256.1.2. Fortran Syntax

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

### 17.2.256.1.3. Fortran 2008 Syntax

    USE mpi_f08
    MPI_Mprobe(source, tag, comm, message, status, ierror)
         INTEGER, INTENT(IN) :: source, tag
         TYPE(MPI_Comm), INTENT(IN) :: comm
         TYPE(MPI_Message), INTENT(OUT) :: message
         TYPE(MPI_Status) :: status
         INTEGER, OPTIONAL, INTENT(OUT) :: ierror

## 17.2.256.2. INPUT PARAMETERS

- `source`: Source rank or `MPI_ANY_SOURCE` (integer).

- `tag`: Tag value or `MPI_ANY_TAG` (integer).

- `comm`: Communicator (handle).

## 17.2.256.3. OUTPUT PARAMETERS

- `message`: Message (handle).

- `status`: Status object (status).

- `ierror`: Fortran only: Error status (integer).

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

When MPI_Mprobe returns (from a non-`MPI_PROC_NULL` source), the matched message can then be received by passing the message handle to the MPI_Mrecv or MPI_Imrecv functions.

## 17.2.256.5. 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_Improbe

- MPI_Probe

- MPI_Iprobe

- MPI_Mrecv

- MPI_Imrecv

- MPI_Cancel