Netty4.1源码 :DefaultPromise

 /**
 * 异步操作回调类，当某项操作异步执行时（由另外的线程执行），当前线程当即返回DefaultPromise
 * DefaultPromise.addListener  方法可以添加监听器，当操作完成时被触发
 *　或者调用DefaultPromise.sync()阻塞当前线程，等待操作完成。
 **/

 public class DefaultPromise<V> extends AbstractFuture<V> implements Promise<V> {
    

    private volatile Object result; //结果值
    private final EventExecutor executor;
    /**
     * 监听器对象，可能是一个或多个监听器
     */
    private Object listeners;
   
    

  /**
   * 设置操作成功并通知监听器，如设置失败，抛出异常
   *  
   **/
    public Promise<V> setSuccess(V result) {
        if (setSuccess0(result)) {
            notifyListeners();
            return this;
        }
        throw new IllegalStateException("complete already: " + this);
    }

   /**
   * 设置操作成功并通知监听器，如设置失败，则返回false
   *  
   **/
    public boolean trySuccess(V result) {
        if (setSuccess0(result)) {
            notifyListeners();
            return true;
        }
        return false;
    }

    /**
	* 设置操作失败并通知监听器，如设置失败，抛出异常
	*  
	*/
    public Promise<V> setFailure(Throwable cause) {
        if (setFailure0(cause)) {
            notifyListeners();
            return this;
        }
        throw new IllegalStateException("complete already: " + this, cause);
    }

    /**
	* 设置操作失败并通知监听器，如设置失败，返回false
	*/
    public boolean tryFailure(Throwable cause) {
        if (setFailure0(cause)) {
            notifyListeners();
            return true;
        }
        return false;
    }

 
    /**
	* 操作是否成功
	*/
    public boolean isSuccess() {
        Object result = this.result;
        return result != null && result != UNCANCELLABLE && !(result instanceof CauseHolder);
    }

    /**
	* 操作是否可以取消
	*/
    public boolean isCancellable() {
        return result == null;
    }

    /**
	* 查年操作的抛出的异常
	*/
    public Throwable cause() {
        Object result = this.result;
        return (result instanceof CauseHolder) ? ((CauseHolder) result).cause : null;
    }

    //添加或移除监听器
    public Promise<V> addListener(GenericFutureListener<? extends Future<? super V>> listener) {}
    public Promise<V> addListeners(GenericFutureListener<? extends Future<? super V>>... listeners) {}
    public Promise<V> removeListener(final GenericFutureListener<? extends Future<? super V>> listener) {}
    public Promise<V> removeListeners(final GenericFutureListener<? extends Future<? super V>>... listeners) {}

    /**
	* 阻塞当前线程，等待异步任务操作完成
	*
	**/
    public Promise<V> await() throws InterruptedException {
        if (isDone()) {
            return this;
        }

        if (Thread.interrupted()) {
            throw new InterruptedException(toString());
        }

        checkDeadLock();

        synchronized (this) {
            while (!isDone()) {
                incWaiters();
                try {
                    wait();
                } finally {
                    decWaiters();
                }
            }
        }
        return this;
    }

    /**
	* 阻塞当前线程，等待异步任务操作完成，接受中断请求
	*
	**/
    public Promise<V> awaitUninterruptibly() {
        if (isDone()) {
            return this;
        }

        checkDeadLock();

        boolean interrupted = false;
        synchronized (this) {
            while (!isDone()) {
                incWaiters();
                try {
                    wait();
                } catch (InterruptedException e) {
                    // Interrupted while waiting.
                    interrupted = true;
                } finally {
                    decWaiters();
                }
            }
        }

        if (interrupted) {
            Thread.currentThread().interrupt();
        }

        return this;
    }

    /**
	* 阻塞当前线程，等待异步任务操作完成，如果在等待时间花费完成之后，异步任务还未完成则不在等待（退出阻塞）
	*
	**/
    public boolean await(long timeout, TimeUnit unit) throws InterruptedException {
        return await0(unit.toNanos(timeout), true);
    }

     /**
	* 阻塞当前线程，等待异步任务操作完成，如果在等待时间花费完成之后，异步任务还未完成则不在等待（退出阻塞）
	*
	**/
    public boolean await(long timeoutMillis) throws InterruptedException {
        return await0(MILLISECONDS.toNanos(timeoutMillis), true);
    }
 

    /**
	* 获取异步操作的结果值
	**/
    public V getNow() {
        Object result = this.result;
        if (result instanceof CauseHolder || result == SUCCESS) {
            return null;
        }
        return (V) result;
    }
 

    /**
	* 任务是否被取消
	**/
    public boolean isCancelled() {
        return isCancelled0(result);
    }

     /**
	* 异步任务是否执行完成
	**/
    public boolean isDone() {
        return isDone0(result);
    }
	
    /**
	* 阻塞直至异步任务完成，或抛出异步任务出错的异常
	*/
    public Promise<V> sync() throws InterruptedException {
        await();
        rethrowIfFailed();
        return this;
    }
	/**
	* 阻塞直至异步任务完成，或抛出异步任务出错的异常，支持中断
	*/
    public Promise<V> syncUninterruptibly() {
        awaitUninterruptibly();
        rethrowIfFailed();
        return this;
    }
 

    /**
     * Notify a listener that a future has completed.
     * <p>
     * This method has a fixed depth of {@link #MAX_LISTENER_STACK_DEPTH} that will limit recursion to prevent
     * {@link StackOverflowError} and will stop notifying listeners added after this threshold is exceeded.
     * @param eventExecutor the executor to use to notify the listener {@code listener}.
     * @param future the future that is complete.
     * @param listener the listener to notify.
     */
    protected static void notifyListener(
            EventExecutor eventExecutor, final Future<?> future, final GenericFutureListener<?> listener) {
        
        notifyListenerWithStackOverFlowProtection(eventExecutor, future, listener);
    }
	/**
	* 通知监听器
	**/
	
    private void notifyListeners() {
        EventExecutor executor = executor();
        if (executor.inEventLoop()) {
            final InternalThreadLocalMap threadLocals = InternalThreadLocalMap.get();
            final int stackDepth = threadLocals.futureListenerStackDepth();
            if (stackDepth < MAX_LISTENER_STACK_DEPTH) {
                threadLocals.setFutureListenerStackDepth(stackDepth + 1);
                try {
                    notifyListenersNow();
                } finally {
                    threadLocals.setFutureListenerStackDepth(stackDepth);
                }
                return;
            }
        }

        safeExecute(executor, new Runnable() {
            @Override
            public void run() {
                notifyListenersNow();
            }
        });
    }

   //ignore some code
}