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   Copyright 1998-2022 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

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   you may not use this file except in compliance with the License.
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.. index:: pair: threaded_cancel/1; Built-in predicate
.. _predicates_threaded_cancel_1:

``threaded_cancel/1``
=====================

Description
-----------

::

   threaded_cancel(Tag)

Cancels a tagged threaded call. When there is no asynchronous call with the
given tag, calling this predicate succeeds assuming the asynchronous call
have already terminated or canceled. The threaded call identifier tag is
generated by calls to the :ref:`threaded_call/2 <predicates_threaded_call_1_2>`
and :ref:`threaded_once/2 <predicates_threaded_once_1_2>` predicates. Tags
shall be regarded as an opaque term; users shall not rely on its type.

.. note::

   This predicate requires a :term:`backend Prolog compiler` providing
   compatible multi-threading primitives. The value of the read-only
   :ref:`threads <flag_threads>` flag is set to ``supported`` when that
   is the case.

Modes and number of proofs
--------------------------

::

   threaded_cancel(+nonvar) - one

Errors
------

| ``Tag`` is a variable:
|     ``instantiation_error``

Examples
--------

(none)

.. seealso::

   :ref:`predicates_threaded_call_1_2`,
   :ref:`predicates_threaded_exit_1_2`,
   :ref:`predicates_threaded_ignore_1`,
   :ref:`predicates_threaded_once_1_2`,
   :ref:`predicates_threaded_1`
