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   Copyright 1998-2021 Paulo Moura <pmoura@logtalk.org>
   SPDX-License-Identifier: Apache-2.0

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.. index:: pair: threaded_call/1-2; Built-in predicate
.. _predicates_threaded_call_1_2:

``threaded_call/1-2``
=====================

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

::

   threaded_call(Goal)
   threaded_call(Goal, Tag)

Proves ``Goal`` asynchronously using a new thread. The argument can be a
message sending goal. Calls to this predicate always succeeds and return
immediately. The results (success, failure, or exception) are sent back
to the message queue of the object containing the call (:term:`this`) and
can be retrieved by calling the
:ref:`threaded_exit/1 <predicates_threaded_exit_1_2>` predicate.

The ``threaded_call/2`` variant returns a threaded call identifier tag that
can be used with the :ref:`threaded_exit/2 <predicates_threaded_exit_1_2>`
and :ref:`predicates_threaded_cancel_1` predicates. Tags shall be regarded
as opaque terms; users shall not rely on its type.

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

::

   threaded_call(@callable) - one
   threaded_call(@callable, --nonvar) - one

Errors
------

| ``Goal`` is a variable:
|     ``instantiation_error``
| ``Goal`` is neither a variable nor a callable term:
|     ``type_error(callable, Goal)``
| ``Tag`` is not a variable:
|     ``type_error(variable, Goal)``

Examples
--------

| Prove ``Goal`` asynchronously in a new thread:
|     ``threaded_call(Goal)``
| Prove ``::Message`` asynchronously in a new thread:
|     ``threaded_call(::Message)``
| Prove ``Object::Message`` asynchronously in a new thread:
|     ``threaded_call(Object::Message)``

.. seealso::

   :ref:`predicates_threaded_exit_1_2`,
   :ref:`predicates_threaded_ignore_1`,
   :ref:`predicates_threaded_once_1_2`,
   :ref:`predicates_threaded_peek_1_2`,
   :ref:`predicates_threaded_cancel_1`,
   :ref:`predicates_threaded_1`,
   :ref:`directives_synchronized_1`
