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Utility classes for Jetty
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//
//  ========================================================================
//  Copyright (c) 1995-2022 Mort Bay Consulting Pty Ltd and others.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

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 implements Future, Promise
{
    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);
    }

    @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);
    }
}