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package com.firefly.utils.concurrent;

import java.util.concurrent.CompletableFuture;

/**
 * 

* A callback abstraction that handles completed/failed events of asynchronous * operations. *

*

*

* Semantically this is equivalent to an optimise Promise<Void>, but * callback is a more meaningful name than EmptyPromise *

*/ public interface Callback { /** * Instance of Adapter that can be used when the callback methods need an * empty implementation without incurring in the cost of allocating a new * Adapter object. */ Callback NOOP = new Callback() { }; /** *

* Callback invoked when the operation completes. *

* * @see #failed(Throwable) */ default void succeeded() { } /** *

* Callback invoked when the operation fails. *

* * @param x the reason for the operation failure */ default void failed(Throwable x) { } /** * @return True if the callback is known to never block the caller */ default boolean isNonBlocking() { return false; } /** *

* Creates a non-blocking callback from the given incomplete * CompletableFuture. *

*

* When the callback completes, either succeeding or failing, the * CompletableFuture is also completed, respectively via * {@link CompletableFuture#complete(Object)} or * {@link CompletableFuture#completeExceptionally(Throwable)}. *

* * @param completable the CompletableFuture to convert into a callback * @return a callback that when completed, completes the given * CompletableFuture */ static Callback from(CompletableFuture completable) { return from(completable, false); } /** *

* Creates a callback from the given incomplete CompletableFuture, with the * given {@code blocking} characteristic. *

* * @param completable the CompletableFuture to convert into a callback * @param blocking whether the callback is blocking * @return a callback that when completed, completes the given * CompletableFuture */ static Callback from(CompletableFuture completable, boolean blocking) { if (completable instanceof Callback) return (Callback) completable; return new Callback() { @Override public void succeeded() { completable.complete(null); } @Override public void failed(Throwable x) { completable.completeExceptionally(x); } @Override public boolean isNonBlocking() { return !blocking; } }; } /** * Callback interface that declares itself as non-blocking */ interface NonBlocking extends Callback { @Override default boolean isNonBlocking() { return true; } } class Nested implements Callback { private final Callback callback; public Nested(Callback callback) { this.callback = callback; } public Nested(Nested nested) { this.callback = nested.callback; } public Callback getCallback() { return callback; } @Override public void succeeded() { callback.succeeded(); } @Override public void failed(Throwable x) { callback.failed(x); } @Override public boolean isNonBlocking() { return callback.isNonBlocking(); } } /** *

* A CompletableFuture that is also a Callback. *

*/ class Completable extends CompletableFuture implements Callback { private final boolean blocking; public Completable() { this(false); } public Completable(boolean blocking) { this.blocking = blocking; } @Override public void succeeded() { complete(null); } @Override public void failed(Throwable x) { completeExceptionally(x); } @Override public boolean isNonBlocking() { return !blocking; } } }




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