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.. rst-class:: align-right

directive

.. index:: pair: synchronized/1; Directive .. _directives_synchronized_1:

synchronized/1

Description

::

synchronized(Name/Arity) synchronized((Name/Arity, ...)) synchronized([Name/Arity, ...])

synchronized(Name//Arity) synchronized((Name//Arity, ...)) synchronized([Name//Arity, ...])

Declares :term:`synchronized <synchronized predicate>` predicates and synchronized grammar rule non-terminals. The most common use is for predicates that have side effects (e.g. asserting or retracting clauses for a dynamic predicate) in multi-threaded applications. A synchronized predicate (or synchronized non-terminal) is protected by a mutex in order to allow for thread synchronization when proving a call to the predicate (or non-terminal).

All predicates (and non-terminals) declared in the same synchronized directive share the same mutex. In order to use a separate mutex for each predicate (non-terminal) so that they are independently synchronized, a per-predicate synchronized directive must be used.

.. warning::

Declaring a predicate synchronized implicitly makes it deterministic. When using a single-threaded :term:`backend Prolog compiler`, calls to synchronized predicates behave as wrapped by the standard :ref:methods_once_1 meta-predicate.

Note that synchronized predicates cannot be declared :ref:`dynamic <directives_dynamic_1>` (when necessary, declare the predicates updating the dynamic predicates as synchronized).

Template and modes

::

synchronized(+predicate_indicator_term) synchronized(+non_terminal_indicator_term)

Examples

::

:- synchronized(db_update/1).

:- synchronized((write_stream/2, read_stream/2)).

:- synchronized([add_to_queue/2, remove_from_queue/2]).

.. seealso::

:ref:methods_predicate_property_2