``random``
==========

This library provides portable random number generators and an
abstraction over native backend Prolog compiler random number generator
if available.

API documentation
-----------------

Open the
`../../docs/library_index.html#random <../../docs/library_index.html#random>`__
link in a web browser.

Loading
-------

To load all entities in this library, load the ``loader.lgt`` file:

::

   | ?- logtalk_load(random(loader)).

Testing
-------

To test this library predicates, load the ``tester.lgt`` file:

::

   | ?- logtalk_load(random(tester)).

Usage
-----

The ``random`` object implements portable random number generator and
supports multiple random number generators, using different seeds, by
defining derived objects. For example:

::

   :- object(my_random_generator_1,
       extends(random)).

       :- initialization(::reset_seed).

   :- end_object.

The ``fast_random`` object also implements a portable random number
generator but does not support deriving multiple random number
generators, which makes it a bit faster than the ``random`` object.

The ``random`` and ``fast_random`` objects manage the random number
generator seed using internal dynamic state. The predicates that update
the seed are declared as synchronized (when running on Prolog backends
that support threads). Still, care must be taken when using these
objects from multi-threaded applications as there is not portable
solution to protect seed updates from signals and prevent inconsistent
state when threads are canceled.

The ``backend_random`` object abstracts the native backend Prolog
compiler random number generator for the basic ``random/1``,
``get_seed/1``, and ``set_seed/1`` predicates providing a portable
implementation for the remaining predicates. This makes the object
stateless, which can allow reliable use from multiple threads. Consult
the backend Prolog compiler documentation for details on its random
number generator properties. Note that several of the supported backend
Prolog systems, notably B-Prolog, CxProlog, ECLiPSe, JIProlog, Lean
Prolog, Qu-Prolog, and Quintus Prolog, do not provide implementations
for both the ``get_seed/1`` and ``set_seed/1`` predicates and calling
these predicates simply succeed without performing any action.
