MPI_COMM_IDUP(3)				     Open MPI					  MPI_COMM_IDUP(3)

MPI_Comm_idup — Start the nonblocking duplication of an existing communicator with all its cached information.

SYNTAX
   C Syntax
	  #include <mpi.h>

	  int MPI_Comm_idup(MPI_Comm comm, MPI_Comm *newcomm, MPI_Request *request)

   Fortran Syntax
	  USE MPI
	  ! or the older form: INCLUDE 'mpif.h'
	  MPI_COMM_IDUP(COMM, NEWCOMM, REQUEST, IERROR)
	       INTEGER COMM, NEWCOMM, REQUEST, IERROR

   Fortran 2008 Syntax
	  USE mpi_f08
	  MPI_Comm_idup(comm, newcomm, request, ierror)
	       TYPE(MPI_Comm), INTENT(IN) :: comm
	       TYPE(MPI_Comm), INTENT(OUT) :: newcomm
	       TYPE(MPI_Request), INTENT(OUT) :: request
	       INTEGER, OPTIONAL, INTENT(OUT) :: ierror

INPUT PARAMETER
       • comm: Communicator (handle).

OUTPUT PARAMETERS
       • newcomm: Copy of comm (handle).

       • request: Communication request (handle).

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

DESCRIPTION
       MPI_Comm_idup  starts  the  nonblocking	duplication  of	 an existing communicator comm with associated key
       values. For each key value, the respective copy callback function determines the attribute value associated
       with this key in the new communicator; one particular action that a copy callback may take is to delete the
       attribute from the new communicator. Returns in newcomm a new communicator with the same group, any  copied
       cached  information,  but a new context (see the “Functionality” subsection of the “Caching” section in the
       “Groups, Contexts, and Communicators” chapter in the MPI Standard <https://www.mpi-forum.org/docs/>).   The
       communicator returned in newcomm will not be available until the request is complete.

       The  completion	of  a  communicator  duplication  request  can be determined by calling any of MPI_Wait <#
       mpi-wait>, MPI_Waitany <#mpi-waitany>, MPI_Test <#mpi-test>, or MPI_Testany <#mpi-testany> with the request
       returned by this function.

NOTES
       This operation is used to provide a parallel library call with a duplicate communication space that has the
       same properties as the original communicator. This includes any attributes (see below) and topologies  (see
       the  “Process  Topologies”  chapter  in	the MPI Standard <https://www.mpi-forum.org/docs/>).  This call is
       valid even if there are pending point-to-point communications involving the communicator	 comm.	A  typical
       call  might  involve  an	 MPI_Comm_idup	at  the	 beginning  of	the parallel call, and an MPI_Comm_free <#
       mpi-comm-free> of that duplicated communicator at the end  of  the  call.   Other  models  of  communicator
       management are also possible.

       This call applies to both intra- and intercommunicators.

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

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_Comm_dup <#mpi-comm-dup>

	  • MPI_Comm_dup_with_info <#mpi-comm-dup-with-info>

Copyright
       2003-2026, The Open MPI Community

						   Mar 05, 2026					  MPI_COMM_IDUP(3)
