1.异步发送API接口

 public void send(final Message message, final AsyncSendCallback callback)

2.实现类分析

public void send(final Message message, final AsyncSendCallback callback) {
        checkState();
        send(message, transportConfig.getSendTimeout(), callback);
    }
	
	
@Override
public void send(final Message message, final int timeout, final AsyncSendCallback callback)  {
	checkState();
	if (message == null) {
		return;
	}
	List<Message> messages = new ArrayList<Message>();
	messages.add(message);
	send(messages, timeout, callback);
}	
	
@Override
public void send(final List<Message> messages, final int timeout, final AsyncSendCallback callback) throws JMQException {
	checkState();
	send(messages, timeout, true, callback);
}	

3.调用核心send方法

private void send(final List<Message> messages, final int timeout, final boolean isAsync, final AsyncSendCallback callback)  {
       ......
        // 发送，出错重试
       transport.async(putMessage, (int) sendTimeout, callback);
    }

transport.async接口

void async(Command command, int timeout, CommandCallback callback)

@Override
    public void async(final Command command, final int timeout, final CommandCallback callback) throws JMQException {
        checkState();
        client.async(channel, command, timeout, callback); // 传递了channel，此处的channel是netty包中的channel
    }

看看具体怎么用netty中的channel与后端异步通信

@Override
    public void async(final Channel channel, final Command command, final int timeout, CommandCallback callback)  {
        if (channel == null) {
            throw new IllegalArgumentException("The argument channel must not be null");
        }

        if (command == null) {
            throw new IllegalArgumentException("The argument command must not be null");
        }

        if (callback == null) {
            throw new IllegalArgumentException("The argument callback must not be null");
        }

        int sendTimeout = timeout <= 0 ? config.getSendTimeout() : timeout;
        // 获取信号量
        acquireSemaphore(asyncSemaphore, command, sendTimeout);

        // 发送请求
        final ResponseFuture responseFuture =
                new ResponseFuture(channel, command, sendTimeout, callback, asyncSemaphore, null);
        futures.put(command.getRequestId(), responseFuture);
        // 应答回来的时候或超时会自动释放command
		// channel写数据往后端的同时，返回个future对象，future对象会自动用到注册的listener
        channel.writeAndFlush(command).addListener(new ResponseListener(responseFuture, futures));
    }