javascalautils.concurrent

Interface Future<T>

Type Parameters:

T - The type this Future will hold as result

public interface Future<T>

A Future that will hold the result of an asynchronous computation.
The Future is paired with an instance of Promise which is also the way to get hold of a Future.
One can see a Future as a holder for a value-to-be, not yet available but accessible sometime in the future.
The preferred way to get hold of the value-to-be is to register a listener on any of the provided listener types since this allows for asynchronous non-blocking operations.

• onComplete(Consumer)
• onSuccess(Consumer)
• onFailure(Consumer)

It is possible to register multiple listeners to several/same listener type.
One can register a listener both before and after a Future has been completed.
Should the Future already be completed when the listener is added it is fired immediately.
The guarantee is that a listener is only fired once.

All operations on this class are non-blocking, i.e. allowing for proper asynchronous/non-blocking programming patterns.
With one exception, for situations where it is necessary to maintain synchronous/blocking behavior the method result(long, TimeUnit) is provided.

For real short and consistent programming one can use the apply(ThrowableFunction0) method to provide a function that will be executed in the future.
The result of the function will be reported to the Future returned by the method.

 Future<Integer> resultSuccess = Future.apply(() -> 9 / 3); // The Future will at some point contain: Success(3)
 Future<Integer> resultFailure = Future.apply(() -> 9 / 0); // The Future will at some point contain: Failure(ArithmeticException)
 

Since:

1.2

Author:

Peter Nerg

Method Summary

Modifier and Type	Method and Description
static <T> Future<T>	apply(ThrowableFunction0<T> function) Allows for easy creation of asynchronous computations that will be executed in the future.
static <T> Future<T>	apply(ThrowableFunction0<T> function, Executor executor) Allows for easy creation of asynchronous computations that will be executed in the future.
static <T> Future<T>	failed(Throwable throwable) Creates a failed Future with the provided Throwable.
Future<T>	filter(java.util.function.Predicate<T> predicate) Creates a new Future that will filter the successful value of this instance once it is completed.
<R> Future<R>	flatMap(java.util.function.Function<T,Future<R>> function) Creates a new Future that will hold the mapped successful value of this instance once it is completed.
void	forEach(java.util.function.Consumer<T> consumer) Asynchronously processes the value in the Future once it is available.
static <T> Future<T>	fromTry(Try<T> result) Creates a completed Future with the provided Try.
boolean	isCompleted() Check if this Future is completed, with a value or an exception.
<R> Future<R>	map(java.util.function.Function<T,R> function) Creates a new Future that will hold the mapped successful value of this instance once it is completed.
void	onComplete(java.util.function.Consumer<Try<T>> completeHandler) Register a handler to be invoked if the Future gets completed with a value or a failure.
void	onFailure(java.util.function.Consumer<Throwable> failureHandler) Register a handler to be invoked if the Future gets completed with an exception.
void	onSuccess(java.util.function.Consumer<T> successHandler) Register a handler to be invoked if the Future gets completed with a value.
Future<T>	recover(java.util.function.Function<Throwable,T> recoverFunction) Creates a new Future that in case this Future is a 'failure' will apply the function to recover the 'failure' to a 'success'.
T	result(long duration, TimeUnit timeUnit) Blocks and waits for this Future to complete.
static <T> Future<java.util.stream.Stream<T>>	sequence(java.util.stream.Stream<Future<T>> stream) Turns a Stream of Futures into a single Future containing a Stream with all the results from the Futures.
static <T> Future<T>	successful(T value) Creates a successful Future with the provided value.
<R> Future<R>	transform(java.util.function.Function<T,R> onSuccess, java.util.function.Function<Throwable,Throwable> onFailure) Creates a new Future that will hold the transformed successful value of this instance once it is completed.
static <T,R> Future<java.util.stream.Stream<R>>	traverse(java.util.stream.Stream<T> stream, java.util.function.Function<T,Future<R>> function) Takes a Stream of values and applies the provided function to them in parallel resulting in a Future containing a Stream with the mapped values.
Option<Try<T>>	value() The current (completed or not) value of the future.

Method Detail

apply

static <T> Future<T> apply(ThrowableFunction0<T> function)

Allows for easy creation of asynchronous computations that will be executed in the future.
The method will use the Executors.getDefault() method to get hold of the default Executor to use for executing the provided job.
Simple examples:

 Future<Integer> resultSuccess = Future.apply(() -> 9 / 3); // The Future will at some point contain: Success(3)
 Future<Integer> resultFailure = Future.apply(() -> 9 / 0); // The Future will at some point contain: Failure(ArithmeticException)
 

Type Parameters:

T - The type for the Future

Parameters:

function - The function to render either the value T or raise an exception.

Returns:

The future that will hold the result provided by the function

Since:

1.3

apply

static <T> Future<T> apply(ThrowableFunction0<T> function,
                           Executor executor)

Allows for easy creation of asynchronous computations that will be executed in the future.
The method will use the provided Executor for executing the provided job.
Simple examples:

 Future<Integer> resultSuccess = Future.apply(() -> 9 / 3, someExecutor); // The Future will at some point contain: Success(3)
 Future<Integer> resultFailure = Future.apply(() -> 9 / 0, someExecutor); // The Future will at some point contain: Failure(ArithmeticException)
 

Type Parameters:

T - The type for the Future

Parameters:

function - The function to render either the value T or raise an exception.

executor - The executor to use to compute/execute the Future holding the provided function

Returns:

The future that will hold the result provided by the function

Since:

1.4

failed

static <T> Future<T> failed(Throwable throwable)

Creates a failed Future with the provided Throwable.

Type Parameters:

T - The type for the Future

Parameters:

throwable - The throwable to complete the Future with.

Returns:

The completed Future holding the provided Throwable

Since:

1.5

successful

static <T> Future<T> successful(T value)

Creates a successful Future with the provided value.

Type Parameters:

T - The type for the Future

Parameters:

value - The value to complete the Future with.

Returns:

The completed Future holding the provided value

Since:

1.5

fromTry

static <T> Future<T> fromTry(Try<T> result)

Creates a completed Future with the provided Try.
The Future can therefore be either Success or Failure.

Type Parameters:

T - The type for the Future

Parameters:

result - The Success/Failure to complete the Future with.

Returns:

The completed Future holding the provided result

Since:

1.5

sequence

static <T> Future<java.util.stream.Stream<T>> sequence(java.util.stream.Stream<Future<T>> stream)

Turns a Stream of Futures into a single Future containing a Stream with all the results from the Futures.
Allows for easy management of multiple Futures.
Note, should any Future in the Stream fail the entire sequence fails.
An empty input Stream will result in a Future containing an empty result Stream.

Type Parameters:

T - The type for the Stream in the resulting Future

Parameters:

stream - The Stream with Futures

Returns:

A single Future containing the Stream of results

Since:

1.5

traverse

static <T,R> Future<java.util.stream.Stream<R>> traverse(java.util.stream.Stream<T> stream,
                                                         java.util.function.Function<T,Future<R>> function)

Takes a Stream of values and applies the provided function to them in parallel resulting in a Future containing a Stream with the mapped values.
Can be used to run a mapping operation in parallel e.g.:

 import static javascalautils.FutureCompanion.Future;
 
 Stream<String> stream = ...; // Stream with strings
 Future<Stream<Integer>> future = Future.traverse(stream, v -> Future(() -> v.length()));
 

Type Parameters:

T - The type for the input Stream

R - The type for the Stream in the resulting Future

Parameters:

stream - The Stream with values

function - The function to be applied to all values of the Stream

Returns:

A single Future containing the Stream of results

Since:

1.5

isCompleted

boolean isCompleted()

Check if this Future is completed, with a value or an exception.

Returns:

true if completed, false otherwise.

value

Option<Try<T>> value()

The current (completed or not) value of the future.
This is a non-blocking method, it will return the current state/value of the Future.
There are three possible outcomes:

• The future has not been completed -> None is returned
• The execution of the Future was successful -> Some with a Success containing the value of the executed job
• The execution failed and an exception was reported -> Some with a Failure containing the Throwable

Returns:

An Option with the result.

onFailure

void onFailure(java.util.function.Consumer<Throwable> failureHandler)

Register a handler to be invoked if the Future gets completed with an exception.
If the Future has already been completed the notification will happen in the current thread.
Multiple handlers can be registered, without any guarantee of notification order.
Each individual event handler will only be invoked once.

Parameters:

failureHandler - Consumer to invoke.

onSuccess

void onSuccess(java.util.function.Consumer<T> successHandler)

Register a handler to be invoked if the Future gets completed with a value.
If the Future has already been completed the notification will happen in the current thread.
Multiple handlers can be registered, without any guarantee of notification order.
Each individual event handler will only be invoked once.

Parameters:

successHandler - Consumer to invoke.

onComplete

void onComplete(java.util.function.Consumer<Try<T>> completeHandler)

Register a handler to be invoked if the Future gets completed with a value or a failure.
If the Future has already been completed the notification will happen in the current thread.
Multiple handlers can be registered, without any guarantee of notification order.
Each individual event handler will only be invoked once.

Parameters:

completeHandler - Consumer to invoke.

forEach

void forEach(java.util.function.Consumer<T> consumer)

Asynchronously processes the value in the Future once it is available.
Only successful Futures are reported to the consumer.
This is pretty much the same as onSuccess(Consumer) but is here for completion keeping a consistent look and feel.

Parameters:

consumer - The consumer to digest the result

map

<R> Future<R> map(java.util.function.Function<T,R> function)

Creates a new Future that will hold the mapped successful value of this instance once it is completed.
Unsuccessful Futures will not be mapped, they are kept unsuccessful as they are.

Type Parameters:

R - The type for the value held by the mapped future

Parameters:

function - The function to apply

Returns:

The mapped Future

flatMap

<R> Future<R> flatMap(java.util.function.Function<T,Future<R>> function)

Creates a new Future that will hold the mapped successful value of this instance once it is completed.
Unsuccessful Futures will not be mapped, they are kept unsuccessful as they are.

Type Parameters:

R - The type for the value held by the mapped future

Parameters:

function - The function to apply

Returns:

The mapped Future

filter

Future<T> filter(java.util.function.Predicate<T> predicate)

Creates a new Future that will filter the successful value of this instance once it is completed.
The possible outcomes are:

• This Future is successful -> predicate matches -> The filtered future is completed with the value.
• This Future is successful -> predicate fails -> The filtered future is failed with NoSuchElementException.
• This Future is failure -> The failure is passed on to the filtered Future.

Parameters:

predicate - The predicate to apply

Returns:

The filtered Future

transform

<R> Future<R> transform(java.util.function.Function<T,R> onSuccess,
                        java.util.function.Function<Throwable,Throwable> onFailure)

Creates a new Future that will hold the transformed successful value of this instance once it is completed.
Successful futures are transformed with the onSuccess function and unsuccessful/failure futures are transformed with onFailure.

Type Parameters:

R - The type for the value held by the mapped future

Parameters:

onSuccess - The function to apply on a 'successful' result

onFailure - The function to apply on a 'failure' result

Returns:

The mapped Future

Since:

1.3

recover

Future<T> recover(java.util.function.Function<Throwable,T> recoverFunction)

Creates a new Future that in case this Future is a 'failure' will apply the function to recover the 'failure' to a 'success'.
Should this Future be a 'success' the value is propagated as-is.
E.g.

 Future<String> future = ...
 Future<String> recovered = future.recover(t -> t.getMessage());
 

In case of 'future' being successful then that value is passed on to 'recovered', in case of failure then the recover function kicks in and returns the message from the throwable.

Parameters:

recoverFunction - The function to apply in case of a 'failure'

Returns:

The recovered Future

Since:

1.3

result

T result(long duration,
         TimeUnit timeUnit)
  throws Throwable,
         TimeoutException

Blocks and waits for this Future to complete.
Returns the result of a successful Future or throws the exception in case of a failure.
The methods blocks for at most the provided duration.
If the Future is already completed the method returns immediately.

Parameters:

duration - The duration to block

timeUnit - The unit for the duration

Returns:

The result in case successful

Throws:

Throwable - The error reported in case of a failure

TimeoutException - In case the waiting time is passed