目錄

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概述

JDK.Future

Netty.Future

ChannelFuture

Promise

繼承關系

源碼分析

AbstractFuture

CompleteFuture

DefaultPromise

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概述

Future代表了異步操作的結果，Netty的Future對JDK的Future進行了擴展。

JDK.Future

僅定義了是否完成以及是否取消的狀態判斷以及get方法。

public interface Future<V> {boolean cancel(boolean mayInterruptIfRunning);boolean isCancelled();boolean isDone();V get() throws InterruptedException, ExecutionException;V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; }

Netty.Future

增加了：

• 結果狀態
• 監聽器管理
• sync
• await

public interface Future<V> extends java.util.concurrent.Future<V> {//statusboolean isSuccess();boolean isCancellable();Throwable cause();//listenerFuture<V> addListener(GenericFutureListener<? extends Future<? super V>> listener);Future<V> addListeners(GenericFutureListener<? extends Future<? super V>>... listeners);Future<V> removeListener(GenericFutureListener<? extends Future<? super V>> listener);Future<V> removeListeners(GenericFutureListener<? extends Future<? super V>>... listeners);//syncFuture<V> sync() throws InterruptedException;Future<V> syncUninterruptibly();//awaitFuture<V> await() throws InterruptedException;Future<V> awaitUninterruptibly();boolean await(long timeout, TimeUnit unit) throws InterruptedException;boolean await(long timeoutMillis) throws InterruptedException;boolean awaitUninterruptibly(long timeout, TimeUnit unit);boolean awaitUninterruptibly(long timeoutMillis);V getNow();@Overrideboolean cancel(boolean mayInterruptIfRunning); }

ChannelFuture

增加了相關channel信息。

狀態信息：

public interface ChannelFuture extends Future<Void> {Channel channel();boolean isVoid(); }

Promise

Promise相對Future增加了設置狀態的方法。

public interface Promise<V> extends Future<V> {//設置操作狀態方法Promise<V> setSuccess(V result);boolean trySuccess(V result);Promise<V> setFailure(Throwable cause);boolean tryFailure(Throwable cause);boolean setUncancellable();@OverridePromise<V> addListener(GenericFutureListener<? extends Future<? super V>> listener);@OverridePromise<V> addListeners(GenericFutureListener<? extends Future<? super V>>... listeners);@OverridePromise<V> removeListener(GenericFutureListener<? extends Future<? super V>> listener);@OverridePromise<V> removeListeners(GenericFutureListener<? extends Future<? super V>>... listeners);@OverridePromise<V> await() throws InterruptedException;@OverridePromise<V> awaitUninterruptibly();@OverridePromise<V> sync() throws InterruptedException;@OverridePromise<V> syncUninterruptibly(); }

繼承關系

源碼分析

AbstractFuture<V>

get()方法調用await()方法。

public abstract class AbstractFuture<V> implements Future<V> {@Overridepublic V get() throws InterruptedException, ExecutionException {await();Throwable cause = cause();if (cause == null) {return getNow();}if (cause instanceof CancellationException) {throw (CancellationException) cause;}throw new ExecutionException(cause);}@Overridepublic V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException {if (await(timeout, unit)) {Throwable cause = cause();if (cause == null) {return getNow();}if (cause instanceof CancellationException) {throw (CancellationException) cause;}throw new ExecutionException(cause);}throw new TimeoutException();} }

CompleteFuture<V>

代表一個Future已經完成。

內部包含一個EventExecutor，用于注冊事件監聽器

public abstract class CompleteFuture<V> extends AbstractFuture<V> {private final EventExecutor executor;protected CompleteFuture(EventExecutor executor) {this.executor = executor;}@Overridepublic Future<V> addListener(GenericFutureListener<? extends Future<? super V>> listener) {if (listener == null) {throw new NullPointerException("listener");}DefaultPromise.notifyListener(executor(), this, listener);return this;}@Overridepublic Future<V> addListeners(GenericFutureListener<? extends Future<? super V>>... listeners) {if (listeners == null) {throw new NullPointerException("listeners");}for (GenericFutureListener<? extends Future<? super V>> l: listeners) {if (l == null) {break;}DefaultPromise.notifyListener(executor(), this, l);}return this;} }

DefaultPromise<V>

設置狀態內部使用了一個AtomicReferenceFieldUpdater

??? private static final AtomicReferenceFieldUpdater<DefaultPromise, Object> RESULT_UPDATER =
??????????? AtomicReferenceFieldUpdater.newUpdater(DefaultPromise.class, Object.class, "result");

??

? private boolean setValue0(Object objResult) {
??????? if (RESULT_UPDATER.compareAndSet(this, null, objResult) ||
??????????? RESULT_UPDATER.compareAndSet(this, UNCANCELLABLE, objResult)) {
??????????? if (checkNotifyWaiters()) {
??????????????? notifyListeners();
??????????? }
??????????? return true;
??????? }
??????? return false;
??? }

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