.. _mpi_comm_delete_attr:

MPI_Comm_delete_attr
====================

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:ref:`MPI_Comm_delete_attr` |mdash| Deletes attribute value associated with a
key.

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.. include:: ./bindings/mpi_comm_delete_attr.rst

INPUT PARAMETER
---------------

* ``comm_keyval`` : Key value (integer).

OUTPUT PARAMETER
----------------

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

DESCRIPTION
-----------

:ref:`MPI_Comm_delete_attr` deletes an attribute from cache by key. This
function invokes the attribute delete function ``delete_fn`` specified
when the ``comm_keyval`` was created. The call will fail if the
``delete_fn`` function returns an error code other than ``MPI_SUCCESS``.

Whenever a communicator is replicated using the function
:ref:`MPI_Comm_dup`, all callback copy functions for attributes that are
currently set are invoked (in arbitrary order). Whenever a communicator
is deleted using the function :ref:`MPI_Comm_free`, all callback delete
functions for attributes that are currently set are invoked. This
function is the same as :ref:`MPI_Attr_delete` but is needed to match the
``comm``\ unicator-specific functions introduced in the MPI-2 standard.
The use of :ref:`MPI_Attr_delete` is deprecated.

NOTES
-----

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.

ERRORS
------

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