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.. rst-class:: align-right

built-in predicate

.. index:: pair: threaded/1; Built-in predicate .. _predicates_threaded_1:

threaded/1

Description

::

threaded(Conjunction) threaded(Disjunction)

Proves each goal in a conjunction or a disjunction of goals in its own thread. This meta-predicate is deterministic and opaque to cuts. The predicate argument is not flattened.

When the argument is a conjunction of goals, a call to this predicate blocks until either all goals succeed, one of the goals fail, or one of the goals generate an exception; the failure of one of the goals or an exception on the execution of one of the goals results in the termination of the remaining threads. The predicate call is true iff all goals are true. The predicate call fails if all goals fails. When one of the goals throw an exception, the predicate call re-throws that exception.

When the argument is a disjunction of goals, a call to this predicate blocks until either one of the goals succeeds or all the goals fail or throw exceptions; the success of one of the goals results in the termination of the remaining threads. The predicate call is true iff one of the goals is true. The predicate call fails if all goals fails. When no goal succeeds and one of the goals throws an exception, the predicate call re-throws that exception.

When the predicate argument is neither a conjunction not a disjunction of goals, no threads are used. In this case, the predicate call is equivalent to a once/1 predicate call.

A dedicated message queue is used per call of this predicate to collect the individual goal results.

.. 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(0)

Modes and number of proofs

::

threaded(+callable) - zero_or_one

Errors

| Goals is a variable: | instantiation_error | A goal in Goals is a variable: | instantiation_error | Goals is neither a variable nor a callable term: | type_error(callable, Goals) | A goal Goal in Goals is neither a variable nor a callable term: | type_error(callable, Goal)

Examples

| Prove a conjunction of goals, each one in its own thread: | threaded((Goal, Goals)) | Prove a disjunction of goals, each one in its own thread: | threaded((Goal; Goals))

.. seealso::

:ref:predicates_threaded_call_1_2, :ref:predicates_threaded_once_1_2, :ref:predicates_threaded_ignore_1, :ref:directives_synchronized_1