1 类的继承关系

2 代码分析

package io.netty.channel;

import io.netty.channel.ChannelFlushPromiseNotifier.FlushCheckpoint;
import io.netty.util.concurrent.DefaultPromise;
import io.netty.util.concurrent.EventExecutor;
import io.netty.util.concurrent.Future;
import io.netty.util.concurrent.GenericFutureListener;

import static io.netty.util.internal.ObjectUtil.checkNotNull;

/**
 * The default {@link ChannelPromise} implementation.  It is recommended to use {@link Channel#newPromise()} to create
 * a new {@link ChannelPromise} rather than calling the constructor explicitly.
 */
public class DefaultChannelPromise extends DefaultPromise<Void> implements ChannelPromise, FlushCheckpoint {

    private final Channel channel;
    private long checkpoint;

    /**
     * Creates a new instance.
     *
     * @param channel
     *        the {@link Channel} associated with this future
     */
    public DefaultChannelPromise(Channel channel) {
        this.channel = checkNotNull(channel, "channel");
    }

    /**
     * Creates a new instance.
     *
     * @param channel
     *        the {@link Channel} associated with this future
     */
    public DefaultChannelPromise(Channel channel, EventExecutor executor) {
        super(executor);
        this.channel = checkNotNull(channel, "channel");
    }

    @Override
    protected EventExecutor executor() {
        EventExecutor e = super.executor();
        if (e == null) {
            return channel().eventLoop();
        } else {
            return e;
        }
    }

    @Override
    public Channel channel() {
        return channel;
    }

    @Override
    public ChannelPromise setSuccess() {
        return setSuccess(null);
    }

    @Override
    public ChannelPromise setSuccess(Void result) {
        super.setSuccess(result);
        return this;
    }

    @Override
    public boolean trySuccess() {
        return trySuccess(null);
    }

    @Override
    public ChannelPromise setFailure(Throwable cause) {
        super.setFailure(cause);
        return this;
    }

    @Override
    public ChannelPromise addListener(GenericFutureListener<? extends Future<? super Void>> listener) {
        super.addListener(listener);
        return this;
    }

    @Override
    public ChannelPromise addListeners(GenericFutureListener<? extends Future<? super Void>>... listeners) {
        super.addListeners(listeners);
        return this;
    }

    @Override
    public ChannelPromise removeListener(GenericFutureListener<? extends Future<? super Void>> listener) {
        super.removeListener(listener);
        return this;
    }

    @Override
    public ChannelPromise removeListeners(GenericFutureListener<? extends Future<? super Void>>... listeners) {
        super.removeListeners(listeners);
        return this;
    }

    @Override
    public ChannelPromise sync() throws InterruptedException {
        super.sync();
        return this;
    }

    @Override
    public ChannelPromise syncUninterruptibly() {
        super.syncUninterruptibly();
        return this;
    }

    @Override
    public ChannelPromise await() throws InterruptedException {
        super.await();
        return this;
    }

    @Override
    public ChannelPromise awaitUninterruptibly() {
        super.awaitUninterruptibly();
        return this;
    }

    @Override
    public long flushCheckpoint() {
        return checkpoint;
    }

    @Override
    public void flushCheckpoint(long checkpoint) {
        this.checkpoint = checkpoint;
    }

    @Override
    public ChannelPromise promise() {
        return this;
    }

    @Override
    protected void checkDeadLock() {
        if (channel().isRegistered()) {
            super.checkDeadLock();
        }
    }

    @Override
    public ChannelPromise unvoid() {
        return this;
    }

    @Override
    public boolean isVoid() {
        return false;
    }
}

2.1 isVoid

它的定义在父类中：

/**
 * Returns {@code true} if this {@link ChannelFuture} is a void future and so not allow to call any of the
 * following methods:
 * <ul>
 *     <li>{@link #addListener(GenericFutureListener)}</li>
 *     <li>{@link #addListeners(GenericFutureListener[])}</li>
 *     <li>{@link #await()}</li>
 *     <li>{@link #await(long, TimeUnit)} ()}</li>
 *     <li>{@link #await(long)} ()}</li>
 *     <li>{@link #awaitUninterruptibly()}</li>
 *     <li>{@link #sync()}</li>
 *     <li>{@link #syncUninterruptibly()}</li>
 * </ul>
 */
boolean isVoid();

如果return返回true表示这个ChannelFuture是一个void，且不能调用这个写方法。

然后DefaultChannelPromise覆写了这个方法，return false。

2.2 unvoid

它的定义在父类ChannelPromise#unvoid中：

/**
 * Returns a new {@link ChannelPromise} if {@link #isVoid()} returns {@code true} otherwise itself.
 */
ChannelPromise unvoid();

这个地方，DefaultChannelPromise按照它的语义return this。

3.3 checkDeadLock

它的定义在DefaultPromise#checkDeadLock中这个地方DefaultChannelPromise覆写了这个方法，如果channel是注册的，则调用父类的DefaultPromise#checkDeadLock。

其中private final Channel channel;是一个私有变量。

3.4 checkpoint

private long checkpoint;这个私有变量不知道干嘛的。

3.5 executor() 方法

它的覆盖了父类的DefaultPromise#executor的方法：

如果DefaultPromise的private final EventExecutor executor;为null，则会返回Channel里的eventLoop。