C Syntax

       2003-2025, The Open MPI Community

                                                  Jun 07, 2025                                  MPI_COMM_FREE(3)

       This  operation  marks  the communicator object for deallocation. The handle is set to MPI_COMM_NULL. Any
       pending operations that use this communicator will complete normally; the object is actually  deallocated
       only  if  there  are  no  other  active  references  to  it.  This call applies to intracommunicators and
       intercommunicators. Upon actual deallocation, the delete callback functions  for  all  cached  attributes
       (see  the “Caching” section in the “Groups, Contexts, and Communicators” chapter in the MPIStandard) are
       called in arbitrary order.

       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 MPImanpage for a full list of MPIerrorcodes.

       See the Error Handling section of the MPI-3.1 standard for more information.

       SEEALSO:

          • MPI_Comm_delete_attr

       • comm: Communicator to be destroyed (handle).

       Note that it is not defined by the MPI standard what happens if the delete_fn callback invokes other  MPI
       functions.  In  Open  MPI,  it  is not valid for delete_fn callbacks (or any of their children) to add or
       delete attributes on the same object on which the delete_fn callback is being invoked.

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

CSyntax
          #include <mpi.h>

          int MPI_Comm_free(MPI_Comm *comm)

   FortranSyntax
          USE MPI
          ! or the older form: INCLUDE 'mpif.h'
          MPI_COMM_FREE(COMM, IERROR)
               INTEGER COMM, IERROR

   Fortran2008Syntax
          USE mpi_f08
          MPI_Comm_free(comm, ierror)
               TYPE(MPI_Comm), INTENT(INOUT) :: comm
               INTEGER, OPTIONAL, INTENT(OUT) :: ierror