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MPI_Comm_dup(3)			      MPI		       MPI_Comm_dup(3)

NAME
       MPI_Comm_dup -  Duplicates an existing communicator

SYNOPSIS
       int MPI_Comm_dup(MPI_Comm comm, MPI_Comm	*newcomm)

INPUT PARAMETERS
       comm   -	communicator (handle)

OUTPUT PARAMETERS
       newcomm
	      -	copy of	comm (handle)

NOTES
       This routine is used to create a	new communicator that has a new	commu-
       nication	 context but contains the same group of	processes as the input
       communicator.  Since all	MPI communication is performed within a	commu-
       nicator (specifies as the group of processes plus  the  context),  this
       routine	provides an effective way to create a private communicator for
       use by a	software module	or library.  In	particular, no library routine
       should use MPI_COMM_WORLD as the	communicator; instead, a duplicate  of
       a user-specified	communicator should always be used.  For more informa-
       tion, see Using MPI, 2nd	edition.

       Because	this routine essentially produces a copy of a communicator, it
       also copies any attributes that have been defined on the	input communi-
       cator, using the	attribute copy function	specified by the copy_function
       argument	to MPI_Keyval_create .	This is	particularly  useful  for  (a)
       attributes that describe	some property of the group associated with the
       communicator,  such  as its interconnection topology and	(b) communica-
       tors that are given back	to the user; the attributes in this  case  can
       track subsequent	MPI_Comm_dup operations	on this	communicator.

THREAD AND INTERRUPT SAFETY
       This  routine  is  thread-safe.	 This  means  that this	routine	may be
       safely used by multiple threads without the need	for any	 user-provided
       thread  locks.  However,	the routine is not interrupt safe.  Typically,
       this is due to the use of memory	allocation routines such as malloc  or
       other  non-MPICH	 runtime  routines  that are themselves	not interrupt-
       safe.

NOTES FOR FORTRAN
       All MPI routines	in Fortran (except for MPI_WTIME and MPI_WTICK )  have
       an  additional  argument	ierr at	the end	of the argument	list.  ierr is
       an integer and has the same meaning as the return value of the  routine
       in  C.	In Fortran, MPI	routines are subroutines, and are invoked with
       the call	statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm )	are of type INTEGER in
       Fortran.

ERRORS
       All MPI routines	(except	MPI_Wtime and  MPI_Wtick  )  return  an	 error
       value;  C routines as the value of the function and Fortran routines in
       the last	argument.  Before the value is returned, the current MPI error
       handler is called.  By default, this error handler aborts the MPI  job.
       The error handler may be	changed	with MPI_Comm_set_errhandler (for com-
       municators),  MPI_File_set_errhandler  (for files), and MPI_Win_set_er-
       rhandler	(for RMA windows).  The	MPI-1 routine  MPI_Errhandler_set  may
       be  used	 but  its  use	is  deprecated.	  The predefined error handler
       MPI_ERRORS_RETURN may be	used to	cause error  values  to	 be  returned.
       Note  that MPI does not guarantee that an MPI program can continue past
       an error; however, MPI implementations will attempt to  continue	 when-
       ever possible.

       MPI_SUCCESS
	      -	No error; MPI routine completed	successfully.
       MPI_ERR_ARG
	      -	Invalid	argument.  Some	argument is invalid and	is not identi-
	      fied by a	specific error class (e.g., MPI_ERR_RANK ).
       MPI_ERR_COMM
	      -	 Invalid communicator.	A common error is to use a null	commu-
	      nicator in a call	(not even allowed in MPI_Comm_rank ).
       MPI_ERR_OTHER
	      -	Other error; use  MPI_Error_string  to	get  more  information
	      about this error code.

SEE ALSO
       MPI_Comm_free,	 MPI_Keyval_create,   MPI_Attr_put,   MPI_Attr_delete,
       MPI_Comm_create_keyval, MPI_Comm_set_attr, MPI_Comm_delete_attr

				   2/3/2025		       MPI_Comm_dup(3)

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