# 17.2.54. MPI_Comm_disconnect

MPI_Comm_disconnect — Deallocates communicator object and sets handle to MPI_COMM_NULL.

## 17.2.54.1. SYNTAX

### 17.2.54.1.1. C Syntax

    #include <mpi.h>

    int MPI_Comm_disconnect(MPI_Comm *comm)

### 17.2.54.1.2. Fortran Syntax

    USE MPI
    ! or the older form: INCLUDE 'mpif.h'

    MPI_COMM_DISCONNECT(COMM, IERROR)
        INTEGER COMM, IERROR

### 17.2.54.1.3. Fortran 2008 Syntax

    USE mpi_f08

    MPI_Comm_disconnect(comm, ierror)
        TYPE(MPI_Comm), INTENT(INOUT) :: comm
        INTEGER, OPTIONAL, INTENT(OUT) :: ierror

### 17.2.54.1.4. INPUT/OUTPUT PARAMETER

- `comm` : Communicator (handle).

## 17.2.54.2. OUTPUT PARAMETER

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

## 17.2.54.3. DESCRIPTION

MPI_Comm_disconnect waits for all pending communication on comm to complete internally, deallocates the communicator object, and sets the handle to MPI_COMM_NULL. It is a collective operation. It may not be called with the communicator MPI_COMM_WORLD or MPI_COMM_SELF. MPI_Comm_disconnect may be called only if all communication is complete and matched, so that buffered data can be delivered to its destination. This requirement is the same as for MPI_Finalize. MPI_Comm_disconnect has the same action as MPI_Comm_free, except that it waits for pending communication to finish internally and enables the guarantee about the behavior of disconnected processes.

## 17.2.54.4. NOTES

To disconnect two processes you may need to call MPI_Comm_disconnect, MPI_Win_free, and MPI_File_close to remove all communication paths between the two processes. Note that it may be necessary to disconnect several communicators (or to free several windows or files) before two processes are completely independent.

## 17.2.54.5. 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_Comm_connect