motan源码分析八：涉及到底层的客户端调用

之前我们分析了客户端调用服务端的源码，但是没有涉及到通讯层和序列化层，本文将之前讲过的内容做一次串联。

1.上层通过动态代理调用refer的call，每个refer又对应一个nettyclient，下面来看一下nettyclient的调用服务端操作

	private Response request(Request request, boolean async) throws TransportException {
		Channel channel = null;

		Response response = null;

		try {
			// return channel or throw exception(timeout or connection_fail)
			channel = borrowObject();//向连接池拿连接

			if (channel == null) {
				LoggerUtil.error("NettyClient borrowObject null: url=" + url.getUri() + " "
						+ MotanFrameworkUtil.toString(request));
				return null;
			}

			// async request
			response = channel.request(request);//调用channel的request
			// return channel to pool
			returnObject(channel);//归还连接
		} catch (Exception e) {
			LoggerUtil.error(
					"NettyClient request Error: url=" + url.getUri() + " " + MotanFrameworkUtil.toString(request), e);
			//TODO 对特定的异常回收channel
			invalidateObject(channel);//销毁坏的连接

			if (e instanceof MotanAbstractException) {
				throw (MotanAbstractException) e;
			} else {
				throw new MotanServiceException("NettyClient request Error: url=" + url.getUri() + " "
						+ MotanFrameworkUtil.toString(request), e);
			}
		}

		// aysnc or sync result
		response = asyncResponse(response, async);//处理response

		return response;
	}

2.nettychannel的request操作

	public Response request(Request request) throws TransportException {
	    int timeout = nettyClient.getUrl().getMethodParameter(request.getMethodName(), request.getParamtersDesc(),
	            URLParamType.requestTimeout.getName(), URLParamType.requestTimeout.getIntValue());
		if (timeout <= 0) {
               throw new MotanFrameworkException("NettyClient init Error: timeout(" + timeout + ") <= 0 is forbid.",
                       MotanErrorMsgConstant.FRAMEWORK_INIT_ERROR);
           }
		NettyResponseFuture response = new NettyResponseFuture(request, timeout, this.nettyClient);//创建异步response对象
		this.nettyClient.registerCallback(request.getRequestId(), response);//将此response存入到map，处理完后，会移出
		ChannelFuture writeFuture = this.channel.write(request);//向服务端传递request对象，写之前会进行序列化的操作

		boolean result = writeFuture.awaitUninterruptibly(timeout, TimeUnit.MILLISECONDS);//标识是否成功

		if (result && writeFuture.isSuccess()) {
			response.addListener(new FutureListener() {//增加response的监听器
				@Override
				public void operationComplete(Future future) throws Exception {
					if (future.isSuccess() || (future.isDone() && ExceptionUtil.isBizException(future.getException()))) {
						// 成功的调用
						nettyClient.resetErrorCount();//成功
					} else {
						// 失败的调用
						nettyClient.incrErrorCount();//对失败次数+1，如果同一个client连续失败达到所有的连接次数时，标识此client不可用，由心跳管理器负责恢复此client的可用状态
					}
				}
			});
			return response;//返回此response,此response为异步的response，由业务线程接手后续接收的过程
		}

		writeFuture.cancel();
		response = this.nettyClient.removeCallback(request.getRequestId());//在map中移出此response

		if (response != null) {
			response.cancel();
		}

		// 失败的调用
		nettyClient.incrErrorCount();

		if (writeFuture.getCause() != null) {
			throw new MotanServiceException("NettyChannel send request to server Error: url="
					+ nettyClient.getUrl().getUri() + " local=" + localAddress + " "
					+ MotanFrameworkUtil.toString(request), writeFuture.getCause());
		} else {
			throw new MotanServiceException("NettyChannel send request to server Timeout: url="
					+ nettyClient.getUrl().getUri() + " local=" + localAddress + " "
					+ MotanFrameworkUtil.toString(request));
		}
	}

3.异步的response NettyResponseFuture

	public Object getValue() {
		synchronized (lock) {
			if (!isDoing()) {
				return getValueOrThrowable();//返回成功值或失败
			}

			if (timeout <= 0) {
				try {
					lock.wait();//未接收完毕则一直等待
				} catch (Exception e) {
					cancel(new MotanServiceException("NettyResponseFuture getValue InterruptedException : "
							+ MotanFrameworkUtil.toString(request) + " cost="
							+ (System.currentTimeMillis() - createTime), e));
				}

				// don't need to notifylisteners, because onSuccess or
				// onFailure or cancel method already call notifylisteners
				return getValueOrThrowable();
			} else {
				long waitTime = timeout - (System.currentTimeMillis() - createTime);//等待的时间

				if (waitTime > 0) {
					for (;;) {
						try {
							lock.wait(waitTime);//要么被通知，要么超时
						} catch (InterruptedException e) {
						}

						if (!isDoing()) {
							break;
						} else {
							waitTime = timeout - (System.currentTimeMillis() - createTime);
							if (waitTime <= 0) {
								break;
							}
						}
					}
				}

				if (isDoing()) {
					timeoutSoCancel();
				}
			}
			return getValueOrThrowable();
		}
	}

本章知识点：

1.motan通过NettyResponseFuture来实现在框架层面异步处理同一笔业务，提升了框架的性能；

2.对于连续失败的client，进行下线操作。