# `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 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.