defaultiofuture.java

mina是以Java实现的一个开源的网络程序框架

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 *  Licensed to the Apache Software Foundation (ASF) under one
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 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF licenses this file
 *  to you 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.
 *
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package org.apache.mina.core.future;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.TimeUnit;

import org.apache.mina.core.polling.AbstractPollingIoProcessor;
import org.apache.mina.core.service.IoProcessor;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.util.ExceptionMonitor;


/**
 * A default implementation of {@link IoFuture} associated with
 * an {@link IoSession}.
 * 
 * @author The Apache MINA Project ([e-mail])
 * @version $Rev:671827 $, $Date:2008-06-26 09:49:48 +0100 (jeu., 26 juin 2008) $
 */
public class DefaultIoFuture implements IoFuture {

    /** A number of seconds to wait between two deadlock controls ( 5 seconds ) */
    private static final long DEAD_LOCK_CHECK_INTERVAL = 5000L;

    /** The associated session */
    private final IoSession session;
    
    /** A lock used by the wait() method */
    private final Object lock;
    private IoFutureListener<?> firstListener;
    private List<IoFutureListener<?>> otherListeners;
    private Object result;
    private boolean ready;
    private int waiters;

    /**
     * Creates a new instance associated with an {@link IoSession}.
     *
     * @param session an {@link IoSession} which is associated with this future
     */
    public DefaultIoFuture(IoSession session) {
        this.session = session;
        this.lock = this;
    }

    /**
     * {@inheritDoc}
     */
    public IoSession getSession() {
        return session;
    }

    /**
     * @deprecated Replaced with {@link #awaitUninterruptibly()}.
     */
    @Deprecated
    public void join() {
        awaitUninterruptibly();
    }

    /**
     * @deprecated Replaced with {@link #awaitUninterruptibly(long)}.
     */
    @Deprecated
    public boolean join(long timeoutMillis) {
        return awaitUninterruptibly(timeoutMillis);
    }

    /**
     * {@inheritDoc}
     */
    public IoFuture await() throws InterruptedException {
        synchronized (lock) {
            while (!ready) {
                waiters++;
                try {
                    // Wait for a notify, or if no notify is called,
                    // assume that we have a deadlock and exit the 
                    // loop to check for a potential deadlock.
                    lock.wait(DEAD_LOCK_CHECK_INTERVAL);
                } finally {
                    waiters--;
                    if (!ready) {
                        checkDeadLock();
                    }
                }
            }
        }
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public boolean await(long timeout, TimeUnit unit)
            throws InterruptedException {
        return await(unit.toMillis(timeout));
    }

    /**
     * {@inheritDoc}
     */
    public boolean await(long timeoutMillis) throws InterruptedException {
        return await0(timeoutMillis, true);
    }

    /**
     * {@inheritDoc}
     */
    public IoFuture awaitUninterruptibly() {
        try {
            await0(Long.MAX_VALUE, false);
        } catch ( InterruptedException ie) {
            // Do nothing : this catch is just mandatory by contract
        }
        
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public boolean awaitUninterruptibly(long timeout, TimeUnit unit) {
        return awaitUninterruptibly(unit.toMillis(timeout));
    }

    /**
     * {@inheritDoc}
     */
    public boolean awaitUninterruptibly(long timeoutMillis) {
        try {
            return await0(timeoutMillis, false);
        } catch (InterruptedException e) {
            throw new InternalError();
        }
    }

    /**
     * Wait for the Future to be ready. If the requested delay is 0 or 
     * negative, this method immediately returns the value of the 
     * 'ready' flag. 
     * Every 5 second, the wait will be suspended to be able to check if 
     * there is a deadlock or not.
     * 
     * @param timeoutMillis The delay we will wait for the Future to be ready
     * @param interruptable Tells if the wait can be interrupted or not
     * @return <code>true</code> if the Future is ready
     * @throws InterruptedException If the thread has been interrupted
     * when it's not allowed.
     */
    private boolean await0(long timeoutMillis, boolean interruptable) throws InterruptedException {
        long endTime = System.currentTimeMillis() + timeoutMillis;

        synchronized (lock) {
            if (ready) {
                return ready;
            } else if (timeoutMillis <= 0) {
                return ready;
            }

            waiters++;
            try {
                for (;;) {
                    try {
                        long timeOut = Math.min(timeoutMillis, DEAD_LOCK_CHECK_INTERVAL);
                        lock.wait(timeOut);
                    } catch (InterruptedException e) {
                        if (interruptable) {
                            throw e;
                        }
                    }

                    if (ready) {
                        return true;
                    } else {
                        if (endTime < System.currentTimeMillis()) {
                            return ready;
                        }
                    }
                }
            } finally {
                waiters--;
                if (!ready) {
                    checkDeadLock();
                }
            }
        }
    }

    
    /**
     * 
     * TODO checkDeadLock.
     *
     */
    private void checkDeadLock() {
        // Only read / write / connect / write future can cause dead lock. 
        if (!(this instanceof CloseFuture || this instanceof WriteFuture ||
              this instanceof ReadFuture || this instanceof ConnectFuture)) {
            return;
        }
        
        // Get the current thread stackTrace. 
        // Using Thread.currentThread().getStackTrace() is the best solution,
        // even if slightly less efficient than doing a new Exception().getStackTrace(),
        // as internally, it does exactly the same thing. The advantage of using
        // this solution is that we may benefit some improvement with some
        // future versions of Java.
        StackTraceElement[] stackTrace = Thread.currentThread().getStackTrace();

        // Simple and quick check.
        for (StackTraceElement s: stackTrace) {
            if (AbstractPollingIoProcessor.class.getName().equals(s.getClassName())) {
                IllegalStateException e = new IllegalStateException( "t" );
                e.getStackTrace();
                throw new IllegalStateException(
                    "DEAD LOCK: " + IoFuture.class.getSimpleName() +
                    ".await() was invoked from an I/O processor thread.  " +
                    "Please use " + IoFutureListener.class.getSimpleName() +
                    " or configure a proper thread model alternatively.");
            }
        }

        // And then more precisely.
        for (StackTraceElement s: stackTrace) {
            try {
                Class<?> cls = DefaultIoFuture.class.getClassLoader().loadClass(s.getClassName());
                if (IoProcessor.class.isAssignableFrom(cls)) {
                    throw new IllegalStateException(
                        "DEAD LOCK: " + IoFuture.class.getSimpleName() +
                        ".await() was invoked from an I/O processor thread.  " +
                        "Please use " + IoFutureListener.class.getSimpleName() +
                        " or configure a proper thread model alternatively.");
                }
            } catch (Exception cnfe) {
                // Ignore
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    public boolean isDone() {
        synchronized (lock) {
            return ready;
        }
    }

    /**
     * Sets the result of the asynchronous operation, and mark it as finished.
     */
    public void setValue(Object newValue) {
        synchronized (lock) {
            // Allow only once.
            if (ready) {
                return;
            }

            result = newValue;
            ready = true;
            if (waiters > 0) {
                lock.notifyAll();
            }
        }

        notifyListeners();
    }

    /**
     * Returns the result of the asynchronous operation.
     */
    protected Object getValue() {
        synchronized (lock) {
            return result;
        }
    }

    /**
     * {@inheritDoc}
     */
    public IoFuture addListener(IoFutureListener<?> listener) {
        if (listener == null) {
            throw new NullPointerException("listener");
        }

        boolean notifyNow = false;
        synchronized (lock) {
            if (ready) {
                notifyNow = true;
            } else {
                if (firstListener == null) {
                    firstListener = listener;
                } else {
                    if (otherListeners == null) {
                        otherListeners = new ArrayList<IoFutureListener<?>>(1);
                    }
                    otherListeners.add(listener);
                }
            }
        }

        if (notifyNow) {
            notifyListener(listener);
        }
        return this;
    }

    /**
     * {@inheritDoc}
     */
    public IoFuture removeListener(IoFutureListener<?> listener) {
        if (listener == null) {
            throw new NullPointerException("listener");
        }

        synchronized (lock) {
            if (!ready) {
                if (listener == firstListener) {
                    if (otherListeners != null && !otherListeners.isEmpty()) {
                        firstListener = otherListeners.remove(0);
                    } else {
                        firstListener = null;
                    }
                } else if (otherListeners != null) {
                    otherListeners.remove(listener);
                }
            }
        }

        return this;
    }

    private void notifyListeners() {
        // There won't be any visibility problem or concurrent modification
        // because 'ready' flag will be checked against both addListener and
        // removeListener calls.
        if (firstListener != null) {
            notifyListener(firstListener);
            firstListener = null;

            if (otherListeners != null) {
                for (IoFutureListener<?> l : otherListeners) {
                    notifyListener(l);
                }
                otherListeners = null;
            }
        }
    }

    @SuppressWarnings("unchecked")
    private void notifyListener(IoFutureListener l) {
        try {
            l.operationComplete(this);
        } catch (Throwable t) {
            ExceptionMonitor.getInstance().exceptionCaught(t);
        }
    }
}