Netty中的ChannelFuture

package io.netty.channel;

import io.netty.bootstrap.Bootstrap;
import io.netty.util.concurrent.BlockingOperationException;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.GenericFutureListener;

import java.util.concurrent.TimeUnit;


/**
 * The result of an asynchronous {@link Channel} I/O operation.
 * 一个异步的针对于Channel的IO操作的结果
 * 
 * 

 * All I/O operations in Netty are asynchronous.  It means any I/O calls will
 * return immediately with no guarantee that the requested I/O operation has
 * been completed at the end of the call.  Instead, you will be returned with
 * a {@link ChannelFuture} instance which gives you the information about the
 * result or status of the I/O operation.
 * 在Netty中，所有的IO操作都是异步的。划重点
 * 在这就意味着任何的Io调用都会立刻返回，但是却不保证这个IO操作在调用结束之后是已完成的。
 * 相反，你会得到一个ChannelFuture对象，这个对象携带这Io操作的结果或者状态信息。
 * 
 * 

 * A {@link ChannelFuture} is either uncompleted or completed.
 * When an I/O operation begins, a new future object is created.  The new future
 * is uncompleted initially - it is neither succeeded, failed, nor cancelled
 * because the I/O operation is not finished yet.  If the I/O operation is
 * finished either successfully, with failure, or by cancellation, the future is
 * marked as completed with more specific information, such as the cause of the
 * failure.  Please note that even failure and cancellation belong to the
 * completed state.
 * ChannelFuture是未完成的或者完成的。。
 * 当一个IO操作开始的时候，一个新的Future对象将会被创建。这个新的future是最开始是未完成的，它既不是成功的，失败的，也不是被取消的，
 *以为Io操作到目前还没有结束。
 *如果这个IO操作完成，不管是成功的，失败的，还是取消操作的，这个future都会被标记为完成，它会携带一些具体的信息，例如失败的原因等等。
 *请注意，即使是失败和取消都属于完成的状态。
 *下面是示意图
 * 
 *                                      +---------------------------+
 *                                      | Completed successfully    |
 *                                      +---------------------------+
 *                                 +---->      isDone() = true      |
 * +--------------------------+    |    |   isSuccess() = true      |
 * |        Uncompleted       |    |    +===========================+
 * +--------------------------+    |    | Completed with failure    |
 * |      isDone() = false    |    |    +---------------------------+
 * |   isSuccess() = false    |----+---->      isDone() = true      |
 * | isCancelled() = false    |    |    |       cause() = non-null  |
 * |       cause() = null     |    |    +===========================+
 * +--------------------------+    |    | Completed by cancellation |
 *                                 |    +---------------------------+
 *                                 +---->      isDone() = true      |
 *                                      | isCancelled() = true      |
 *                                      +---------------------------+
 * 
 *
 * Various methods are provided to let you check if the I/O operation has been
 * completed, wait for the completion, and retrieve the result of the I/O
 * operation. It also allows you to add {@link ChannelFutureListener}s so you
 * can get notified when the I/O operation is completed. 
 * 提供了各种各样的方法让你检查IO操作是否已经完成，等待完成，获取IO操作结果。他也允许你添加ChannelFutureListener，
 * 让你能够在IO操作完成之后收到通知
 * 
 * 
Prefer {@link #addListener(GenericFutureListener)} to {@link #await()}
 * 应该使用addListener(GenericFutureListener)这样的方式去获取结果，而不是使用await()方法。
 * 
 * It is recommended to prefer {@link #addListener(GenericFutureListener)} to
 * {@link #await()} wherever possible to get notified when an I/O operation is
 * done and to do any follow-up tasks.
 * 只要IO操作完成，它就推荐使用addListener(GenericFutureListener)来获得通知，然后执行下面的任务。
 * 

 * {@link #addListener(GenericFutureListener)} is non-blocking.  It simply adds
 * the specified {@link ChannelFutureListener} to the {@link ChannelFuture}, and
 * I/O thread will notify the listeners when the I/O operation associated with
 * the future is done.  {@link ChannelFutureListener} yields the best
 * performance and resource utilization because it does not block at all, but
 * it could be tricky to implement a sequential logic if you are not used to
 * event-driven programming.
 * addListener(GenericFutureListener)是非阻塞的。可以非常简单的添加到ChannelFuture中，
 * 当与这个future相关的Io操作完成之后，IO线程将会通知这些监听器。
 * 使用ChannelFutureListener会有最好的性能和资源利用的表现，因为它是完全不阻塞的。
 * 但是它对于实现一个顺序逻辑是不太友好的，如果你没有使用过事件驱动编程的话
 * 

 * By contrast, {@link #await()} is a blocking operation.  Once called, the
 * caller thread blocks until the operation is done.  It is easier to implement
 * a sequential logic with {@link #await()}, but the caller thread blocks
 * unnecessarily until the I/O operation is done and there's relatively
 * expensive cost of inter-thread notification.  Moreover, there's a chance of
 * dead lock in a particular circumstance, which is described below.
 * 相比而言，await()是一个阻塞的操作，一旦被调用，这个调用线程将会一直阻塞，知道操作完成。
 * 它很容易就能够实现顺序逻辑，但是调用者线程会进行没有必要的阻塞，直到io操作完成，所在在夸线程通信当中，这里会产生相对昂贵的成本。
 * 更重要的是，在一个特殊的环境下，会给产生死锁提供一个机会。
 * 
Do not call {@link #await()} inside {@link ChannelHandler}
 * 
不要在ChannelHandler中调用await()方法。
 * The event handler methods in {@link ChannelHandler} are usually called by
 * an I/O thread.  If {@link #await()} is called by an event handler
 * method, which is called by the I/O thread, the I/O operation it is waiting
 * for might never complete because {@link #await()} can block the I/O
 * operation it is waiting for, which is a dead lock.
 * 在ChannelHandle中的事件处理器方法通常会被一个Io线程所调用，如果await()方法被一个事件处理方法调用，然后这个事件处理方法又被IO线程调用，
 * 那么这个IO线程就会一直等待，也许再也不会结束。因为await在等待着Io线程结束，这样就产生了一个死锁
 * 
 * // BAD - NEVER DO THIS
 * 坏的写法，永远也不要这么做
 * {@code @Override}
 * public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
 *     {@link ChannelFuture} future = ctx.channel().close();
 *     future.awaitUninterruptibly();//调用了await方法，等待Io线程执行完毕，而io线程却在等待ChannelHandler的事件方法执行完毕，死锁就产生了。
 *     // Perform post-closure operation
 *     // ...
 * }
 *
 * // GOOD
 * {@code @Override}
 * public void channelRead({@link ChannelHandlerContext} ctx, Object msg) {
 *     {@link ChannelFuture} future = ctx.channel().close();
 *     future.addListener(new {@link ChannelFutureListener}() {
 *         public void operationComplete({@link ChannelFuture} future) {
 *             // Perform post-closure operation
 *             // ...
 *         }
 *     });
 * }
 * 
 * 

 * In spite of the disadvantages mentioned above, there are certainly the cases
 * where it is more convenient to call {@link #await()}. In such a case, please
 * make sure you do not call {@link #await()} in an I/O thread.  Otherwise,
 * {@link BlockingOperationException} will be raised to prevent a dead lock.
 * 如上所述，尽管有这些劣势，但是当然也有一些调用await更加方便的情况，
 * 这样的情况下，请确定你没有在一个IO线程中调用await，否则将会抛出异常来阻塞死锁的发生
 *
 * 
Do not confuse I/O timeout and await timeout
 * 不要混淆IO超时跟等待超时。
 *
 * The timeout value you specify with {@link #await(long)},
 * {@link #await(long, TimeUnit)}, {@link #awaitUninterruptibly(long)}, or
 * {@link #awaitUninterruptibly(long, TimeUnit)} are not related with I/O
 * timeout at all.  If an I/O operation times out, the future will be marked as
 * 'completed with failure,' as depicted in the diagram above.  For example,
 * connect timeout should be configured via a transport-specific option:
 * 等待超时跟io超时完全没有关系。如果一个IO操作超时，这个future将会被用失败标记为完成。就像上面的图描述的那样，
 * 例如连接超时时间应该通过一个特定的传输选项进行配置。
 * 
 * // BAD - NEVER DO THIS
 * {@link Bootstrap} b = ...;
 * {@link ChannelFuture} f = b.connect(...);
 * f.awaitUninterruptibly(10, TimeUnit.SECONDS);//等待超时
 * if (f.isCancelled()) {
 *     // Connection attempt cancelled by user
 * } else if (!f.isSuccess()) {
 *     // You might get a NullPointerException here because the future
 *     // might not be completed yet.
 *     //在这个地方可能会抛出一个空指针异常，因为这个future还没有被标记为完成。
 *     f.cause().printStackTrace();
 * } else {
 *     // Connection established successfully
 * }
 *
 * // GOOD
 * {@link Bootstrap} b = ...;
 * // Configure the connect timeout option.
 * b.option({@link ChannelOption}.CONNECT_TIMEOUT_MILLIS, 10000);
 * IO超时中的连接超时
 * {@link ChannelFuture} f = b.connect(...);
 * f.awaitUninterruptibly();
 * 
 * // Now we are sure the future is completed.
 * assert f.isDone();//io超时后，future就会被标记成done了。
 *
 * if (f.isCancelled()) {
 *     // Connection attempt cancelled by user
 * } else if (!f.isSuccess()) {
 *     f.cause().printStackTrace();
 * } else {
 *     // Connection established successfully
 * }
 * 
 */
public interface ChannelFuture extends Future {

    /**
     * Returns a channel where the I/O operation associated with this
     * future takes place.
     */
    Channel channel();

    @Override
    ChannelFuture addListener(GenericFutureListener> listener);

    @Override
    ChannelFuture addListeners(GenericFutureListener>... listeners);

    @Override
    ChannelFuture removeListener(GenericFutureListener> listener);

    @Override
    ChannelFuture removeListeners(GenericFutureListener>... listeners);

    @Override
    ChannelFuture sync() throws InterruptedException;

    @Override
    ChannelFuture syncUninterruptibly();

    @Override
    ChannelFuture await() throws InterruptedException;

    @Override
    ChannelFuture awaitUninterruptibly();

    /**
     * Returns {@code true} if this {@link ChannelFuture} is a void future and so not allow to call any of the
     * following methods:
     * 

     *     
{@link #addListener(GenericFutureListener)}
     *     
{@link #addListeners(GenericFutureListener[])}
     *     
{@link #await()}
     *     
{@link #await(long, TimeUnit)} ()}
     *     
{@link #await(long)} ()}
     *     
{@link #awaitUninterruptibly()}
     *     
{@link #sync()}
     *     
{@link #syncUninterruptibly()}
     * 
     */
    boolean isVoid();
}