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.. rst-class:: align-right

built-in predicate

.. 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.

.. 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.

Meta-predicate template

::

threaded_call(0) threaded_call(0, *)

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: | uninstantiation_error(Tag)

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