..
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   SPDX-FileCopyrightText: 1998-2024 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
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       http://www.apache.org/licenses/LICENSE-2.0

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.. rst-class:: align-right

**built-in predicate**

.. index:: pair: threaded_engine/1; Built-in predicate
.. _predicates_threaded_engine_1:

``threaded_engine/1``
=====================

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

::

   threaded_engine(Engine)

Enumerates, by backtracking, all existing engines. Engine names shall be
regarded as opaque terms; 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:`engines <flag_engines>` flag is set to ``supported`` when that
   is the case.

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

::

   threaded_engine(?nonvar) - zero_or_more

Errors
------

(none)

Examples
--------

::

   % check that the worker_1 engine exists:
   | ?- threaded_engine(worker_1).

   % write the names of all existing engines:
   | ?- forall(
            threaded_engine(Engine),
            (writeq(Engine), nl)
        ).

.. seealso::

   :ref:`predicates_threaded_engine_create_3`,
   :ref:`predicates_threaded_engine_self_1`,
   :ref:`predicates_threaded_engine_destroy_1`
