FuturePromise.java

//
// ========================================================================
// Copyright (c) 1995-2021 Mort Bay Consulting Pty Ltd and others.
//
// This program and the accompanying materials are made available under the
// terms of the Eclipse Public License v. 2.0 which is available at
// https://www.eclipse.org/legal/epl-2.0, or the Apache License, Version 2.0
// which is available at https://www.apache.org/licenses/LICENSE-2.0.
//
// SPDX-License-Identifier: EPL-2.0 OR Apache-2.0
// ========================================================================
//

package org.eclipse.jetty.util;

import java.io.IOException;
import java.util.concurrent.CancellationException;
import java.util.concurrent.CountDownLatch;
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.AtomicBoolean;

public class FuturePromise<C> implements Future<C>, Promise<C>
{
    private static Throwable COMPLETED = new ConstantThrowable();
    private final AtomicBoolean _done = new AtomicBoolean(false);
    private final CountDownLatch _latch = new CountDownLatch(1);
    private Throwable _cause;
    private C _result;

    public FuturePromise()
    {
    }

    public FuturePromise(C result)
    {
        _cause = COMPLETED;
        _result = result;
        _done.set(true);
        _latch.countDown();
    }

    public FuturePromise(C ctx, Throwable failed)
    {
        _result = ctx;
        _cause = failed;
        _done.set(true);
        _latch.countDown();
    }

    @Override
    public void succeeded(C result)
    {
        if (_done.compareAndSet(false, true))
        {
            _result = result;
            _cause = COMPLETED;
            _latch.countDown();
        }
    }

    @Override
    public void failed(Throwable cause)
    {
        if (_done.compareAndSet(false, true))
        {
            _cause = cause;
            _latch.countDown();
        }
    }

    @Override
    public boolean cancel(boolean mayInterruptIfRunning)
    {
        if (_done.compareAndSet(false, true))
        {
            _result = null;
            _cause = new CancellationException();
            _latch.countDown();
            return true;
        }
        return false;
    }

    @Override
    public boolean isCancelled()
    {
        if (_done.get())
        {
            try
            {
                _latch.await();
            }
            catch (InterruptedException e)
            {
                throw new RuntimeException(e);
            }
            return _cause instanceof CancellationException;
        }
        return false;
    }

    @Override
    public boolean isDone()
    {
        return _done.get() && _latch.getCount() == 0;
    }

    @Override
    public C get() throws InterruptedException, ExecutionException
    {
        _latch.await();
        if (_cause == COMPLETED)
            return _result;
        if (_cause instanceof CancellationException)
            throw (CancellationException)new CancellationException().initCause(_cause);
        throw new ExecutionException(_cause);
    }
    
    /**
     * Return the result if completed successfully
     * or rethrow the Exception
     * 
     * @return the computed result
     * @throws Exception
     */
    public C getOrThrow() throws Exception
    {
        _latch.await();

        if (_cause == COMPLETED)
            return _result;
        if (_cause instanceof Exception)
            throw (Exception)_cause;
        if (_cause instanceof Error)
            throw (Error)_cause;
        
        throw new ExecutionException(_cause);
    }

    @Override
    public C get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException
    {
        if (!_latch.await(timeout, unit))
            throw new TimeoutException();

        if (_cause == COMPLETED)
            return _result;
        if (_cause instanceof TimeoutException)
            throw (TimeoutException)_cause;
        if (_cause instanceof CancellationException)
            throw (CancellationException)new CancellationException().initCause(_cause);
        throw new ExecutionException(_cause);
    }

    public static void rethrow(ExecutionException e) throws IOException
    {
        Throwable cause = e.getCause();
        if (cause instanceof IOException)
            throw (IOException)cause;
        if (cause instanceof Error)
            throw (Error)cause;
        if (cause instanceof RuntimeException)
            throw (RuntimeException)cause;
        throw new RuntimeException(cause);
    }

    @Override
    public String toString()
    {
        return String.format("FutureCallback@%x{%b,%b,%s}", hashCode(), _done.get(), _cause == COMPLETED, _result);
    }
}