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   SPDX-FileCopyrightText: 1998-2025 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_create/3; Built-in predicate
.. _predicates_threaded_engine_create_3:

``threaded_engine_create/3``
============================

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

::

   threaded_engine_create(AnswerTemplate, Goal, Engine)

Creates a new engine for proving the given goal and defines an answer
template for retrieving the goal solution bindings. A message queue for
passing arbitrary terms to the engine is also created. If the name for
the engine is not given, a unique name is generated and returned. 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.

Meta-predicate template
-----------------------

::

   threaded_engine_create(*, 0, *)

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

::

   threaded_engine_create(@term, @callable, @nonvar) - one
   threaded_engine_create(@term, @callable, --nonvar) - one

Errors
------

| ``Goal`` is a variable:
|     ``instantiation_error``
| ``Goal`` is neither a variable nor a callable term:
|     ``type_error(callable, Goal)``
| ``Engine`` is the name of an existing engine:
|     ``permission_error(create, engine, Engine)``

Examples
--------

::

   % create a new engine to enumerate list elements:
   | ?- threaded_engine_create(X, member(X, [1,2,3]), worker_1).

.. seealso::

   :ref:`predicates_threaded_engine_destroy_1`,
   :ref:`predicates_threaded_engine_self_1`,
   :ref:`predicates_threaded_engine_1`,
   :ref:`predicates_threaded_engine_next_2`,
   :ref:`predicates_threaded_engine_next_reified_2`
