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A library for Java that provides re-usable components commonly used by Flow libraries.
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/*
 * This file is part of Flow Commons, licensed under the MIT License (MIT).
 *
 * Copyright (c) 2013 Flow Powered 
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package com.flowpowered.commons;

import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicReference;

public class SimpleFuture implements Future {
    private static Object THROWABLE = new Object();
    private static Object CANCEL = new Object();
    private static Object NULL = new Object();

    private AtomicReference resultRef = new AtomicReference<>(null);
    private AtomicReference throwable = new AtomicReference<>(null);

    @SuppressWarnings("unchecked")
    public boolean setThrowable(Throwable t) {
        if (!throwable.compareAndSet(null, t)) {
            return false;
        }

        if (!resultRef.compareAndSet(null, (T)THROWABLE)) {
            return false;
        }

        synchronized (resultRef) {
            resultRef.notifyAll();
        }

        return true;
    }

    @SuppressWarnings("unchecked")
    public boolean setResult(T result) {
        if (result == null) {
            result = (T)NULL;
        }
        
        if (!resultRef.compareAndSet(null, result)) {
            return false;
        }
        
        synchronized (resultRef) {
            resultRef.notifyAll();
        }
        
        return true;
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean cancel(boolean mayInterruptIfRunning) {
        return resultRef.compareAndSet(null, (T)CANCEL);
    }

    @Override
    public boolean isCancelled() {
        return resultRef.get() == CANCEL;
    }

    @Override
    public boolean isDone() {
        return resultRef.get() != null;
    }

    @Override
    public T get() throws InterruptedException, ExecutionException {
        try {
            return get(0, TimeUnit.MILLISECONDS);
        } catch (TimeoutException toe) {
            throw new IllegalStateException("Attempting to get with an infinite timeout should not cause a timeout exception", toe);
        }
    }

    @Override
    public T get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {
        boolean noTimeout = timeout <= 0;

        long timeoutInMS = unit.toMillis(timeout);

        if (!noTimeout && timeoutInMS <= 0) {
            timeoutInMS = 1;
        }
        long currentTime = System.currentTimeMillis();
        long endTime = currentTime + timeoutInMS;

        while (noTimeout || currentTime < endTime) {
            synchronized (resultRef) {
                T result = resultRef.get();
                if (result != null) {
                    if (result == NULL || result == CANCEL) {
                        return null;
                    }

                    if (result == THROWABLE) {
                        Throwable t = throwable.get();
                        throw new ExecutionException("Exception occured when trying to retrieve the result of this future", t);
                    }

                    return result;
                }

                if (noTimeout) {
                    resultRef.wait();
                } else {
                    resultRef.wait(endTime - currentTime);
                }
            }
            currentTime = System.currentTimeMillis();
        }
        throw new TimeoutException("Wait duration of " + (currentTime - (endTime - timeoutInMS)) + "ms exceeds timeout of " + timeout + unit.toString());
    }
}