directive

# `synchronized/1`

## Description

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

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

Declares synchronized 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 backend Prolog compiler, calls to synchronized predicates behave as wrapped by the standard once/1 meta-predicate.

Note that synchronized predicates cannot be declared dynamic (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]).

See also

predicate_property/2