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Implementation of blocking (IO-Bound) cancellable java.util.concurrent.CompletionStage and related extensions to java.util.concurrent.ExecutorService-s

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/**
 * Copyright 2015-2017 Valery Silaev (http://vsilaev.com)
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.tascalate.concurrent;

import java.lang.reflect.Method;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CompletionStage;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * The {@link CompletablePromise} is an adapter of a {@link CompletableFuture} to the {@link Promise} API 
 * 
 * @author vsilaev
 *
 * @param 
 *   a type of the successfully resolved promise value   
 */
public class CompletablePromise extends AbstractDelegatingPromise> implements Promise {

    public CompletablePromise() {
        this(new CompletableFuture<>());
    }

    public CompletablePromise(CompletableFuture delegate) {
        super(delegate);
    }

    protected boolean onSuccess(T value) {
        return completionStage.complete(value);
    }

    protected boolean onFailure(Throwable ex) {
        return completionStage.completeExceptionally(ex);
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        return completionStage.cancel(mayInterruptIfRunning);
    }

    @Override
    public boolean isCancelled() {
        return completionStage.isCancelled();
    }

    @Override
    public boolean isDone() {
        return completionStage.isDone();
    }

    @Override
    public T get() throws InterruptedException, ExecutionException {
        return completionStage.get();
    }

    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        return completionStage.get(timeout, unit);
    }

    static boolean cancelPromise(final CompletionStage promise, final boolean mayInterruptIfRunning) {
        if (promise instanceof Future) {
            final Future future = (Future) promise;
            return future.cancel(mayInterruptIfRunning);
        } else {
            final Method m = completeExceptionallyMethodOf(promise);
            if (null != m) {
                try {
                    return (Boolean) m.invoke(promise, new CancellationException());
                } catch (final ReflectiveOperationException ex) {
                    return false;
                }
            } else {
                return false;
            }
        }
    }

    private static Method completeExceptionallyMethodOf(CompletionStage promise) {
        try {
            final Class clazz = promise.getClass();
            return clazz.getMethod("completeExceptionally", Throwable.class);
        } catch (ReflectiveOperationException | SecurityException ex) {
            return null;
        }
    }

    @Override
    protected  Promise wrap(CompletionStage original) {
        return new CompletablePromise<>((CompletableFuture)original);
    }
}