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.. This file is part of Logtalk https://logtalk.org/ 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. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
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.. rst-class:: align-right
built-in predicate
.. index:: pair: threaded_once/1-2; Built-in predicate .. _predicates_threaded_once_1_2:
threaded_once/1-2
::
threaded_once(Goal)
threaded_once(Goal, Tag)
Proves Goal
asynchronously using a new thread. Only the first goal
solution is found. The argument can be a message sending goal. This call
always succeeds. The result (success, failure, or exception) is sent
back to the message queue of the object containing the call
(:term:this
).
The threaded_once/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.
.. 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.
::
threaded_once(0)
threaded_once(0, *)
::
threaded_once(@callable)
- one
threaded_once(@callable, --nonvar) - one
| Goal is a variable:
| instantiation_error
| Goal is neither a variable nor a callable term:
| type_error(callable, Goal)
| Tag is not a variable:
| uninstantiation_error(Tag)
| Prove Goal
asynchronously in a new thread:
| threaded_once(Goal)
| Prove ::Message
asynchronously in a new thread:
| threaded_once(::Message)
| Prove Object::Message
asynchronously in a new thread:
| threaded_once(Object::Message)
.. seealso::
:ref:predicates_threaded_call_1_2
,
:ref:predicates_threaded_exit_1_2
,
:ref:predicates_threaded_ignore_1
,
:ref:predicates_threaded_peek_1_2
,
:ref:predicates_threaded_cancel_1
,
:ref:predicates_threaded_1
,
:ref:directives_synchronized_1