在Netty使用ChannelFuture和ChannelPromise进行异步操作的处理
这是官方给出的ChannelFutur描述
1 * | Completed successfully | 2 * +---------------------------+ 3 * +----> isDone() = true | 4 * +--------------------------+ | | isSuccess() = true | 5 * | Uncompleted | | +===========================+ 6 * +--------------------------+ | | Completed with failure | 7 * | isDone() = false | | +---------------------------+ 8 * | isSuccess() = false |----+----> isDone() = true | 9 * | isCancelled() = false | | | cause() = non-null |10 * | cause() = null | | +===========================+11 * +--------------------------+ | | Completed by cancellation |12 * | +---------------------------+13 * +----> isDone() = true |14 * | isCancelled() = true |15 * +---------------------------+
由图可以知道ChannelFutur有四种状态：Uncompleted、Completed successfully、Completed with failure、Completed by cancellation，这几种状态是由isDone、isSuccess、isCancelled、cause这四种方法的返回值决定的。
ChannelFutur接口的定义如下：
1 public interface ChannelFuture extends Future{ 2 Channel channel(); 3 4 ChannelFuture addListener(GenericFutureListener > var1); 5 6 ChannelFuture addListeners(GenericFutureListener... var1); 7 8 ChannelFuture removeListener(GenericFutureListener > var1); 9 10 ChannelFuture removeListeners(GenericFutureListener... var1);11 12 ChannelFuture sync() throws InterruptedException;13 14 ChannelFuture syncUninterruptibly();15 16 ChannelFuture await() throws InterruptedException;17 18 ChannelFuture awaitUninterruptibly();19 20 boolean isVoid();21 }
继承自Netty的Future：
1 public interface Futureextends java.util.concurrent.Future { 2 boolean isSuccess(); 3 4 boolean isCancellable(); 5 6 Throwable cause(); 7 8 Future addListener(GenericFutureListener > var1); 9 10 Future addListeners(GenericFutureListener... var1);11 12 Future removeListener(GenericFutureListener > var1);13 14 Future removeListeners(GenericFutureListener... var1);15 16 Future sync() throws InterruptedException;17 18 Future syncUninterruptibly();19 20 Future await() throws InterruptedException;21 22 Future awaitUninterruptibly();23 24 boolean await(long var1, TimeUnit var3) throws InterruptedException;25 26 boolean await(long var1) throws InterruptedException;27 28 boolean awaitUninterruptibly(long var1, TimeUnit var3);29 30 boolean awaitUninterruptibly(long var1);31 32 V getNow();33 34 boolean cancel(boolean var1);35 }
Netty的Future又继承自JDK的Future：
1 public interface Future{ 2 3 boolean cancel(boolean mayInterruptIfRunning); 4 5 boolean isCancelled(); 6 7 boolean isDone(); 8 9 V get() throws InterruptedException, ExecutionException;10 11 V get(long timeout, TimeUnit unit)12 throws InterruptedException, ExecutionException, TimeoutException;13 }
1 public interface ChannelPromise extends ChannelFuture, Promise{ 2 Channel channel(); 3 4 ChannelPromise setSuccess(Void var1); 5 6 ChannelPromise setSuccess(); 7 8 boolean trySuccess(); 9 10 ChannelPromise setFailure(Throwable var1);11 12 ChannelPromise addListener(GenericFutureListener > var1);13 14 ChannelPromise addListeners(GenericFutureListener... var1);15 16 ChannelPromise removeListener(GenericFutureListener > var1);17 18 ChannelPromise removeListeners(GenericFutureListener... var1);19 20 ChannelPromise sync() throws InterruptedException;21 22 ChannelPromise syncUninterruptibly();23 24 ChannelPromise await() throws InterruptedException;25 26 ChannelPromise awaitUninterruptibly();27 28 ChannelPromise unvoid();29 }
其中Promise接口定义如下：
1 public interface Promiseextends Future { 2 Promise setSuccess(V var1); 3 4 boolean trySuccess(V var1); 5 6 Promise setFailure(Throwable var1); 7 8 boolean tryFailure(Throwable var1); 9 10 boolean setUncancellable();11 12 Promise addListener(GenericFutureListener > var1);13 14 Promise addListeners(GenericFutureListener... var1);15 16 Promise removeListener(GenericFutureListener > var1);17 18 Promise removeListeners(GenericFutureListener... var1);19 20 Promise await() throws InterruptedException;21 22 Promise awaitUninterruptibly();23 24 Promise sync() throws InterruptedException;25 26 Promise syncUninterruptibly();27 }
DefaultChannelPromise定义如下：
1 public class DefaultChannelPromise extends DefaultPromiseimplements ChannelPromise, FlushCheckpoint { 2 3 private final Channel channel; 4 private long checkpoint; 5 6 public DefaultChannelPromise(Channel channel) { 7 this.channel = checkNotNull(channel, "channel"); 8 } 9 10 public DefaultChannelPromise(Channel channel, EventExecutor executor) { 11 super(executor); 12 this.channel = checkNotNull(channel, "channel"); 13 } 14 15 @Override 16 protected EventExecutor executor() { 17 EventExecutor e = super.executor(); 18 if (e == null) { 19 return channel().eventLoop(); 20 } else { 21 return e; 22 } 23 } 24 25 @Override 26 public Channel channel() { 27 return channel; 28 } 29 30 @Override 31 public ChannelPromise setSuccess() { 32 return setSuccess(null); 33 } 34 35 @Override 36 public ChannelPromise setSuccess(Void result) { 37 super.setSuccess(result); 38 return this; 39 } 40 41 @Override 42 public boolean trySuccess() { 43 return trySuccess(null); 44 } 45 46 @Override 47 public ChannelPromise setFailure(Throwable cause) { 48 super.setFailure(cause); 49 return this; 50 } 51 52 @Override 53 public ChannelPromise addListener(GenericFutureListener > listener) { 54 super.addListener(listener); 55 return this; 56 } 57 58 @Override 59 public ChannelPromise addListeners(GenericFutureListener >... listeners) { 60 super.addListeners(listeners); 61 return this; 62 } 63 64 @Override 65 public ChannelPromise removeListener(GenericFutureListener > listener) { 66 super.removeListener(listener); 67 return this; 68 } 69 70 @Override 71 public ChannelPromise removeListeners(GenericFutureListener >... listeners) { 72 super.removeListeners(listeners); 73 return this; 74 } 75 76 @Override 77 public ChannelPromise sync() throws InterruptedException { 78 super.sync(); 79 return this; 80 } 81 82 @Override 83 public ChannelPromise syncUninterruptibly() { 84 super.syncUninterruptibly(); 85 return this; 86 } 87 88 @Override 89 public ChannelPromise await() throws InterruptedException { 90 super.await(); 91 return this; 92 } 93 94 @Override 95 public ChannelPromise awaitUninterruptibly() { 96 super.awaitUninterruptibly(); 97 return this; 98 } 99 100 @Override101 public long flushCheckpoint() {102 return checkpoint;103 }104 105 @Override106 public void flushCheckpoint(long checkpoint) {107 this.checkpoint = checkpoint;108 }109 110 @Override111 public ChannelPromise promise() {112 return this;113 }114 115 @Override116 protected void checkDeadLock() {117 if (channel().isRegistered()) {118 super.checkDeadLock();119 }120 }121 122 @Override123 public ChannelPromise unvoid() {124 return this;125 }126 127 @Override128 public boolean isVoid() {129 return false;130 }131 }
可以看到这个DefaultChannelPromise仅仅是将Channel封装了，而且其基本上所有方法的实现都依赖于父类DefaultPromise
DefaultPromise中的实现是整个ChannelFuture和ChannelPromise的核心所在：
DefaultPromise中有如下几个状态量：
1 private static final int MAX_LISTENER_STACK_DEPTH = Math.min(8,2 SystemPropertyUtil.getInt("io.netty.defaultPromise.maxListenerStackDepth", 8));3 private static final Object SUCCESS = new Object();4 private static final Object UNCANCELLABLE = new Object();5 private static final CauseHolder CANCELLATION_CAUSE_HOLDER = new CauseHolder(ThrowableUtil.unknownStackTrace(6 new CancellationException(), DefaultPromise.class, "cancel(...)"));7 private static final AtomicReferenceFieldUpdater RESULT_UPDATER =8 AtomicReferenceFieldUpdater.newUpdater(DefaultPromise.class, Object.class, "result"); MAX_LISTENER_STACK_DEPTH： 表示最多可执行listeners的数量，默认是8
SUCCESS ：表示异步操作正常完成UNCANCELLABLE：表示异步操作不可取消，并且尚未完成CANCELLATION_CAUSE_HOLDER：表示异步操作取消监听，用于cancel操作，而CauseHolder 的实例对象是用来表示异步操作异常结束，同时保存异常信息：1 private static final class CauseHolder {2 final Throwable cause;3 CauseHolder(Throwable cause) {4 this.cause = cause;5 }6 } DefaultPromise的成员及构造方法定义：
1 public class DefaultPromiseextends AbstractFuture implements Promise { 2 private volatile Object result; 3 private final EventExecutor executor; 4 private Object listeners; 5 private short waiters; 6 private boolean notifyingListeners; 7 8 public DefaultPromise(EventExecutor executor) { 9 this.executor = checkNotNull(executor, "executor");10 }11 }
result：就是前面说的，判断异步操作状态的关键
result的取值有：SUCCESS 、UNCANCELLABLE、CauseHolder以及null (其实还可以是泛型V类型的任意对象，这里暂不考虑)executor：就是Channel绑定的NioEventLoop，在我之前的博客说过，Channel的异步操作都是在NioEventLoop的线程中完成的（[Netty中NioEventLoopGroup的创建源码分析](https://blog.csdn.net/Z_ChenChen/article/details/90567863)）listeners：通过一个Object保存所有对异步操作的监听，用于异步操作的回调waiters：记录阻塞中的listeners的数量notifyingListeners：是否需要唤醒的标志首先来看isDone方法，通过之前的图可以知道，
isDone为false对应了Uncompleted状态，即异步操作尚未完成；isDone为true则代表了异步操作完成，但是还是有三种完成情况，需要结合别的判断方法才能具体知道是哪种情况；isDone方法：
1 @Override2 public boolean isDone() {3 return isDone0(result);4 } 调用isDone0：
1 private static boolean isDone0(Object result) {2 return result != null && result != UNCANCELLABLE;3 } 有如下几种情况：
result等于null，result没有赋值，表示异步操作尚未完成（从这里就能想到异步操作完成，需要调用某个set方法来改变result的状态）result是UNCANCELLABLE状态，表示执行中的异步操作不可取消，当然也就是异步操作尚未完成result不等于null，且不等于UNCANCELLABLE，就表示异步操作完成（包括正常完成，以及异常结束，需要由cause方法进一步判断）isSuccess方法：
1 @Override2 public boolean isSuccess() {3 Object result = this.result;4 return result != null && result != UNCANCELLABLE && !(result instanceof CauseHolder);5 } 由这里可以知道当且仅当result 为SUCCESS状态时，才返回true（其余除UNCANCELLABLE和null的值其实也可以，这里暂不考虑）
isCancelled方法：
1 @Override2 public boolean isCancelled() {3 return isCancelled0(result);4 } 调用isCancelled0方法：
1 private static boolean isCancelled0(Object result) {2 return result instanceof CauseHolder && ((CauseHolder) result).cause instanceof CancellationException;3 } 只有当result是CancellationException的实例时，表示取消异步操作
接着来看cause方法：
1 @Override2 public Throwable cause() {3 Object result = this.result;4 return (result instanceof CauseHolder) ? ((CauseHolder) result).cause : null;5 } 和上面同理，通过判别resul是否是CauseHolder的实现类，若是，将CauseHolder保存的异常返回。
几种状态的判别说完了，下面看一下如何设置这几种状态的：
setSuccess方法：1 @Override2 public PromisesetSuccess(V result) {3 if (setSuccess0(result)) {4 notifyListeners();5 return this;6 }7 throw new IllegalStateException("complete already: " + this);8 }
首先调用setSuccess0方法，其中result的泛型通过DefaultChannelPromise可知是Void，在DefaultChannelPromise中所有的set和try操作参数都是null，这里的result也就不去考虑：
1 private boolean setSuccess0(V result) {2 return setValue0(result == null ? SUCCESS : result);3 } 继续调用setValue0方法：
1 private boolean setValue0(Object objResult) {2 if (RESULT_UPDATER.compareAndSet(this, null, objResult) ||3 RESULT_UPDATER.compareAndSet(this, UNCANCELLABLE, objResult)) {4 checkNotifyWaiters();5 return true;6 }7 return false;8 } 通过CAS操作，将result状态变为SUCCESS
其中checkNotifyWaiters方法：
1 private synchronized void checkNotifyWaiters() {2 if (waiters > 0) {3 notifyAll();4 }5 } 检查waiters的个数，唤醒所有阻塞中的this，sync方法会引起阻塞
回到setSuccess方法中，setSuccess0通过CAS操作，将result状态更新为SUCCESS成功后，调用
notifyListeners方法，唤醒所有listener完成对异步操作的回调listeners是通过addListener方法添加的，用来对异步操作进行侦听：
看到addListener方法：1 @Override 2 public PromiseaddListener(GenericFutureListener > listener) { 3 checkNotNull(listener, "listener"); 4 5 synchronized (this) { 6 addListener0(listener); 7 } 8 9 if (isDone()) {10 notifyListeners();11 }12 13 return this;14 }15 16 @Override17 public Promise addListeners(GenericFutureListener >... listeners) {18 checkNotNull(listeners, "listeners");19 20 synchronized (this) {21 for (GenericFutureListener > listener : listeners) {22 if (listener == null) {23 break;24 }25 addListener0(listener);26 }27 }28 29 if (isDone()) {30 notifyListeners();31 }32 33 return this;34 }
其中GenericFutureListener接口定义如下：
1 public interface GenericFutureListener> extends EventListener {2 /**3 * Invoked when the operation associated with the { @link Future} has been completed.4 *5 * @param future the source { @link Future} which called this callback6 */7 void operationComplete(F future) throws Exception;8 }
可以看到listener其实就是通过operationComplete方法，来完成回调，对Future对象进行处理，由注释可知operationComplete方法是在future操作完成时调用
addListeners方法的实现比较简单，实现核心是在addListener0中：
1 private void addListener0(GenericFutureListener > listener) {2 if (listeners == null) {3 listeners = listener;4 } else if (listeners instanceof DefaultFutureListeners) {5 ((DefaultFutureListeners) listeners).add(listener);6 } else {7 listeners = new DefaultFutureListeners((GenericFutureListener ) listeners, listener);8 }9 } 其中DefaultFutureListeners是将GenericFutureListener对象封装的一个数组：
1 final class DefaultFutureListeners { 2 3 private GenericFutureListener >[] listeners; 4 private int size; 5 private int progressiveSize; 6 7 @SuppressWarnings("unchecked") 8 DefaultFutureListeners( 9 GenericFutureListener > first, GenericFutureListener > second) {10 listeners = new GenericFutureListener[2];11 listeners[0] = first;12 listeners[1] = second;13 size = 2;14 if (first instanceof GenericProgressiveFutureListener) {15 progressiveSize ++;16 }17 if (second instanceof GenericProgressiveFutureListener) {18 progressiveSize ++;19 }20 }21 22 public void add(GenericFutureListener > l) {23 GenericFutureListener >[] listeners = this.listeners;24 final int size = this.size;25 if (size == listeners.length) {26 this.listeners = listeners = Arrays.copyOf(listeners, size << 1);27 }28 listeners[size] = l;29 this.size = size + 1;30 31 if (l instanceof GenericProgressiveFutureListener) {32 progressiveSize ++;33 }34 }35 36 public void remove(GenericFutureListener > l) {37 final GenericFutureListener >[] listeners = this.listeners;38 int size = this.size;39 for (int i = 0; i < size; i ++) {40 if (listeners[i] == l) {41 int listenersToMove = size - i - 1;42 if (listenersToMove > 0) {43 System.arraycopy(listeners, i + 1, listeners, i, listenersToMove);44 }45 listeners[-- size] = null;46 this.size = size;47 48 if (l instanceof GenericProgressiveFutureListener) {49 progressiveSize --;50 }51 return;52 }53 }54 }55 56 public GenericFutureListener >[] listeners() {57 return listeners;58 }59 60 public int size() {61 return size;62 }63 64 public int progressiveSize() {65 return progressiveSize;66 }67 } size：记录listeners的个数
progressiveSize：记录GenericProgressiveFutureListener类型的listeners的个数DefaultFutureListeners 中对数组的操作比较简单，add方法，当size达到数组长度时，进行二倍扩容，其中GenericProgressiveFutureListener继承自GenericFutureListener：
1 public interface GenericProgressiveFutureListener> extends GenericFutureListener { 2 /** 3 * Invoked when the operation has progressed. 4 * 5 * @param progress the progress of the operation so far (cumulative) 6 * @param total the number that signifies the end of the operation when { @code progress} reaches at it. 7 * { @code -1} if the end of operation is unknown. 8 */ 9 void operationProgressed(F future, long progress, long total) throws Exception;10 }
由注释可知operationProgressed是在future操作进行时调用，这里不对GenericProgressiveFutureListener过多讨论
回到addListener0方法，由DefaultFutureListeners就可以知道，实际上通过DefaultFutureListeners管理的一维数组来保存listeners
在addListener方法完成对listener的添加后，还会调用isDone方法检查当前异步操作是否完成，若是完成需要调用notifyListeners，直接唤醒所有listeners完后对异步操作的回调
有add就有remove，removeListener方法：
1 @Override 2 public PromiseremoveListener(final GenericFutureListener > listener) { 3 checkNotNull(listener, "listener"); 4 5 synchronized (this) { 6 removeListener0(listener); 7 } 8 9 return this;10 }11 12 @Override13 public Promise removeListeners(final GenericFutureListener >... listeners) {14 checkNotNull(listeners, "listeners");15 16 synchronized (this) {17 for (GenericFutureListener > listener : listeners) {18 if (listener == null) {19 break;20 }21 removeListener0(listener);22 }23 }24 25 return this;26 }
还是由removeListener0来实现：
1 private void removeListener0(GenericFutureListener > listener) {2 if (listeners instanceof DefaultFutureListeners) {3 ((DefaultFutureListeners) listeners).remove(listener);4 } else if (listeners == listener) {5 listeners = null;6 }7 } 看过之前的内容在看这里就比较简单了，通过DefaultFutureListeners去删除
notifyListeners方法：
1 private void notifyListeners() { 2 EventExecutor executor = executor(); 3 if (executor.inEventLoop()) { 4 final InternalThreadLocalMap threadLocals = InternalThreadLocalMap.get(); 5 final int stackDepth = threadLocals.futureListenerStackDepth(); 6 if (stackDepth < MAX_LISTENER_STACK_DEPTH) { 7 threadLocals.setFutureListenerStackDepth(stackDepth + 1); 8 try { 9 notifyListenersNow();10 } finally {11 threadLocals.setFutureListenerStackDepth(stackDepth);12 }13 return;14 }15 }16 17 safeExecute(executor, new Runnable() {18 @Override19 public void run() {20 notifyListenersNow();21 }22 });23 } 其中executor方法：
1 protected EventExecutor executor() {2 return executor;3 } 用来获取executor轮询线程对象
判断executor是否处于轮询，否则需要通过safeExecute方法处理listeners的侦听，
safeExecute方法：1 private static void safeExecute(EventExecutor executor, Runnable task) {2 try {3 executor.execute(task);4 } catch (Throwable t) {5 rejectedExecutionLogger.error("Failed to submit a listener notification task. Event loop shut down?", t);6 }7 } 这里保证了listeners的侦听回调是异步执行
InternalThreadLocalMap在我之前的博客中说过，是Netty使用的ThreadLocal （）
去线程本地变量中找futureListenerStackDepth（默认为0），判断stackDepth是否小于MAX_LISTENER_STACK_DEPTH，否则也要通过safeExecute方法处理listeners的侦听
核心都是调用notifyListenersNow方法：1 private void notifyListenersNow() { 2 Object listeners; 3 synchronized (this) { 4 // Only proceed if there are listeners to notify and we are not already notifying listeners. 5 if (notifyingListeners || this.listeners == null) { 6 return; 7 } 8 notifyingListeners = true; 9 listeners = this.listeners;10 this.listeners = null;11 }12 for (;;) {13 if (listeners instanceof DefaultFutureListeners) {14 notifyListeners0((DefaultFutureListeners) listeners);15 } else {16 notifyListener0(this, (GenericFutureListener ) listeners);17 }18 synchronized (this) {19 if (this.listeners == null) {20 // Nothing can throw from within this method, so setting notifyingListeners back to false does not21 // need to be in a finally block.22 notifyingListeners = false;23 return;24 }25 listeners = this.listeners;26 this.listeners = null;27 }28 }29 } 先检查是否需要监听，满足条件后，判断listeners是否是DefaultFutureListeners，即包装后的数组
notifyListeners0方法：1 private void notifyListeners0(DefaultFutureListeners listeners) {2 GenericFutureListener [] a = listeners.listeners();3 int size = listeners.size();4 for (int i = 0; i < size; i ++) {5 notifyListener0(this, a[i]);6 }7 } 遍历这个数组，实则调用notifyListener0方法：
1 private static void notifyListener0(Future future, GenericFutureListener l) {2 try {3 l.operationComplete(future);4 } catch (Throwable t) {5 if (logger.isWarnEnabled()) {6 logger.warn("An exception was thrown by " + l.getClass().getName() + ".operationComplete()", t);7 }8 }9 } 这里就可以看到，完成了对operationComplete的回调，处理future
setSuccess结束，再来看trySuccess方法：
1 @Override2 public boolean trySuccess(V result) {3 if (setSuccess0(result)) {4 notifyListeners();5 return true;6 }7 return false;8 } 对比setSuccess来看，只有返回值不一样
setFailure方法：
1 @Override 2 public PromisesetFailure(Throwable cause) { 3 if (setFailure0(cause)) { 4 notifyListeners(); 5 return this; 6 } 7 throw new IllegalStateException("complete already: " + this, cause); 8 } 9 10 private boolean setFailure0(Throwable cause) {11 return setValue0(new CauseHolder(checkNotNull(cause, "cause")));12 }13 14 private boolean setValue0(Object objResult) {15 if (RESULT_UPDATER.compareAndSet(this, null, objResult) ||16 RESULT_UPDATER.compareAndSet(this, UNCANCELLABLE, objResult)) {17 checkNotifyWaiters();18 return true;19 }20 return false;21 }
和setSuccess逻辑一样，只不过CAS操作将状态变为了CauseHolder对象，成功后唤醒listeners对异步操作的回调
tryFailure方法：
1 @Override2 public boolean tryFailure(Throwable cause) {3 if (setFailure0(cause)) {4 notifyListeners();5 return true;6 }7 return false;8 } 也都是一个逻辑
还有一个setUncancellable方法：
1 @Override2 public boolean setUncancellable() {3 if (RESULT_UPDATER.compareAndSet(this, null, UNCANCELLABLE)) {4 return true;5 }6 Object result = this.result;7 return !isDone0(result) || !isCancelled0(result);8 } 若是result状态为null，异步操作尚未结束，直接通过CAS操作将状态变为UNCANCELLABLE
否则若是根据状态来判断 下来看到cancel方法：1 /** 2 * { @inheritDoc} 3 * 4 * @param mayInterruptIfRunning this value has no effect in this implementation. 5 */ 6 @Override 7 public boolean cancel(boolean mayInterruptIfRunning) { 8 if (RESULT_UPDATER.compareAndSet(this, null, CANCELLATION_CAUSE_HOLDER)) { 9 checkNotifyWaiters();10 notifyListeners();11 return true;12 }13 return false;14 } mayInterruptIfRunning正如注释中所说，在这里没有什么作用
还是通过CAS操作，将状态变为CANCELLATION_CAUSE_HOLDER，调用checkNotifyWaiters唤醒因sync阻塞的线程，notifyListeners方法回调listeners的侦听 最后看到sync方法：1 @Override2 public Promisesync() throws InterruptedException {3 await();4 rethrowIfFailed();5 return this;6 }
先调用await方法：
1 @Override 2 public Promiseawait() throws InterruptedException { 3 if (isDone()) { 4 return this; 5 } 6 7 if (Thread.interrupted()) { 8 throw new InterruptedException(toString()); 9 }10 11 checkDeadLock();12 13 synchronized (this) {14 while (!isDone()) {15 incWaiters();16 try {17 wait();18 } finally {19 decWaiters();20 }21 }22 }23 return this;24 }
先判断能否执行（异步操作尚未结束，当前线程没有被中断），然后调用checkDeadLock方法：
1 protected void checkDeadLock() {2 EventExecutor e = executor();3 if (e != null && e.inEventLoop()) {4 throw new BlockingOperationException(toString());5 }6 } 检查轮询线程是否在工作
在synchronized块中以自身为锁，自旋等待异步操作的完成，若是没完成，调用incWaiters方法：
1 private void incWaiters() {2 if (waiters == Short.MAX_VALUE) {3 throw new IllegalStateException("too many waiters: " + this);4 }5 ++waiters;6 } 在小于Short.MAX_VALUE的情况下，对waiters自增，
然后使用wait将自身阻塞，等待被唤醒所以在之前setValue0时，checkNotifyWaiters操作会notifyAll，由此可以知道sync方法的作用：在某一线程中调用sync方法会使得当前线程被阻塞，只有当异步操作执完毕，通过上面的set方法改变状态后，才会调用checkNotifyWaiters方法唤醒当前线程。当从阻塞中被唤醒后调用decWaiters方法：
1 private void decWaiters() {2 --waiters;3 } 使得waiters自减
通过这样一种自旋方式，一直等到isDone成立，结束自旋，进而结束await方法，然后调用rethrowIfFailed方法：1 private void rethrowIfFailed() {2 Throwable cause = cause();3 if (cause == null) {4 return;5 }6 7 PlatformDependent.throwException(cause);8 } 根据异步操作是否有异常，进而使用PlatformDependent抛出异常。
至此Netty中的ChannelFuture和ChannelPromise分析到此全部结束。