ALIBABA DUBBO框架同步调用原理分析

com.taobao.remoting.impl.DefaultClient.java

//同步调用远程接口

public Object invokeWithSync(Object appRequest, RequestControl control) throws RemotingException, InterruptedException {

        byte protocol = getProtocol(control);

        if (!TRConstants.isValidProtocol(protocol)) {

            throw new RemotingException("Invalid serialization protocol [" + protocol + "] on invokeWithSync.");

        }

        ResponseFuture future = invokeWithFuture(appRequest, control);

        return future.get();  //获取结果时让当前线程等待，ResponseFuture其实就是前面说的callback

}

public ResponseFuture invokeWithFuture(Object appRequest, RequestControl control) {

         byte protocol = getProtocol(control);

         long timeout = getTimeout(control);

         ConnectionRequest request = new ConnectionRequest(appRequest);

         request.setSerializeProtocol(protocol);

         Callback2FutureAdapter adapter = new Callback2FutureAdapter(request);

         connection.sendRequestWithCallback(request, adapter, timeout);

         return adapter;

}

Callback2FutureAdapter implements ResponseFuture

public Object get() throws RemotingException, InterruptedException {

synchronized (this) {  // 旋锁

   while (!isDone) {  // 是否有结果了

wait(); //没结果是释放锁，让当前线程处于等待状态

   }

}

if (errorCode == TRConstants.RESULT_TIMEOUT) {

   throw new TimeoutException("Wait response timeout, request["

   + connectionRequest.getAppRequest() + "].");

}

else if (errorCode > 0) {

   throw new RemotingException(errorMsg);

}

else {

   return appResp;

}

}

客户端收到服务端结果后，回调时相关方法，即设置isDone = true并notifyAll()

public void handleResponse(Object _appResponse) {

         appResp = _appResponse; //将远程调用结果设置到callback中来

         setDone();

}

public void onRemotingException(int _errorType, String _errorMsg) {

         errorCode = _errorType;

         errorMsg = _errorMsg;

         setDone();

}

private void setDone() {

         isDone = true;

         synchronized (this) { //获取锁，因为前面wait()已经释放了callback的锁了

             notifyAll(); // 唤醒处于等待的线程

         }

}

com.taobao.remoting.impl.DefaultConnection.java

// 用来存放请求和回调的MAP

private final ConcurrentHashMap<Long, Object[]> requestResidents;

//发送消息出去

void sendRequestWithCallback(ConnectionRequest connRequest, ResponseCallback callback, long timeoutMs) {

         long requestId = connRequest.getId();

         long waitBegin = System.currentTimeMillis();

         long waitEnd = waitBegin + timeoutMs;

         Object[] queue = new Object[4];

         int idx = 0;

         queue[idx++] = waitEnd;

         queue[idx++] = waitBegin;   //用于记录日志

         queue[idx++] = connRequest; //用于记录日志

         queue[idx++] = callback;

         requestResidents.put(requestId, queue); // 记录响应队列

         write(connRequest);

         // 埋点记录等待响应的Map的大小

         StatLog.addStat("TBRemoting-ResponseQueues", "size", requestResidents.size(),

                   1L);

}

public void write(final Object connectionMsg) {

//mina里的IoSession.write()发送消息

         WriteFuture writeFuture = ioSession.write(connectionMsg);

         // 注册FutureListener，当请求发送失败后，能够立即做出响应

         writeFuture.addListener(new MsgWrittenListener(this, connectionMsg));

}

/**

* 在得到响应后，删除对应的请求队列，并执行回调

* 调用者：MINA线程

*/

public void putResponse(final ConnectionResponse connResp) {

         final long requestId = connResp.getRequestId();

         Object[] queue = requestResidents.remove(requestId);

         if (null == queue) {

             Object appResp = connResp.getAppResponse();

             String appRespClazz = (null == appResp) ? "null" : appResp.getClass().getName();

             StringBuilder sb = new StringBuilder();

             sb.append("Not found response receiver for requestId=[").append(requestId).append("],");

             sb.append("from [").append(connResp.getHost()).append("],");

             sb.append("response type [").append(appRespClazz).append("].");

             LOGGER.warn(sb.toString());

             return;

         }

         int idx = 0;

         idx++;

         long waitBegin = (Long) queue[idx++];

         ConnectionRequest connRequest = (ConnectionRequest) queue[idx++];

         ResponseCallback callback = (ResponseCallback) queue[idx++];

         // ** 把回调任务交给业务提供的线程池执行 **

         Executor callbackExecutor = callback.getExecutor();

         callbackExecutor.execute(new CallbackExecutorTask(connResp, callback));

         long duration = System.currentTimeMillis() - waitBegin; // 实际读响应时间

         logIfResponseError(connResp, duration, connRequest.getAppRequest());

}

CallbackExecutorTask

static private class CallbackExecutorTask implements Runnable {

         final ConnectionResponse resp;

         final ResponseCallback callback;

         final Thread createThread;

         CallbackExecutorTask(ConnectionResponse _resp, ResponseCallback _cb) {

             resp = _resp;

             callback = _cb;

             createThread = Thread.currentThread();

         }

         public void run() {

             // 预防这种情况：业务提供的Executor，让调用者线程来执行任务

             if (createThread == Thread.currentThread()

                       && callback.getExecutor() != DIYExecutor.getInstance()) {

                   StringBuilder sb = new StringBuilder();

                   sb.append("The network callback task [" + resp.getRequestId() + "] cancelled, cause:");

                   sb.append("Can not callback task on the network io thhread.");

                   LOGGER.warn(sb.toString());

                   return;

             }

             if (TRConstants.RESULT_SUCCESS == resp.getResult()) {

                   callback.handleResponse(resp.getAppResponse()); //设置调用结果

             }

             else {

                   callback.onRemotingException(resp.getResult(), resp

                            .getErrorMsg());  //处理调用异常

             }

         }

}