开篇

• 这篇文章的目的是讲解在Dubbo 2.6.5版本中TimeoutException的抛出时机，比较简单，抽空看一下能够更好理解抛出的异常信息。

DubboInvoker#doInvoke

public class DubboInvoker<T> extends AbstractInvoker<T> {

    protected Result doInvoke(final Invocation invocation) throws Throwable {
        RpcInvocation inv = (RpcInvocation) invocation;
        final String methodName = RpcUtils.getMethodName(invocation);
        inv.setAttachment(Constants.PATH_KEY, getUrl().getPath());
        inv.setAttachment(Constants.VERSION_KEY, version);

        ExchangeClient currentClient;
        if (clients.length == 1) {
            currentClient = clients[0];
        } else {
            currentClient = clients[index.getAndIncrement() % clients.length];
        }
        try {
            boolean isAsync = RpcUtils.isAsync(getUrl(), invocation);
            boolean isOneway = RpcUtils.isOneway(getUrl(), invocation);
            int timeout = getUrl().getMethodParameter(methodName, Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
            if (isOneway) {
                boolean isSent = getUrl().getMethodParameter(methodName, Constants.SENT_KEY, false);
                currentClient.send(inv, isSent);
                RpcContext.getContext().setFuture(null);
                return new RpcResult();
            } else if (isAsync) {
                ResponseFuture future = currentClient.request(inv, timeout);
                RpcContext.getContext().setFuture(new FutureAdapter<Object>(future));
                return new RpcResult();
            } else {
                RpcContext.getContext().setFuture(null);
                // 发送请求并同步等待结果
                return (Result) currentClient.request(inv, timeout).get();
            }
        } catch (TimeoutException e) {
            throw new RpcException(RpcException.TIMEOUT_EXCEPTION, "Invoke remote method timeout. method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
        } catch (RemotingException e) {
            throw new RpcException(RpcException.NETWORK_EXCEPTION, "Failed to invoke remote method: " + invocation.getMethodName() + ", provider: " + getUrl() + ", cause: " + e.getMessage(), e);
        }
    }
}

• DubboInvoker对象的invoke()方法在同步调用过程中会执行currentClient.request(inv, timeout).get()。
• currentClient.request(inv, timeout)负责发送请求，get()负责同步等待结果。

HeaderExchangeChannel#request

final class HeaderExchangeChannel implements ExchangeChannel {

    public ResponseFuture request(Object request, int timeout) throws RemotingException {
        if (closed) {
            throw new RemotingException(this.getLocalAddress(), null, "Failed to send request " + request + ", cause: The channel " + this + " is closed!");
        }
        // create request.
        Request req = new Request();
        req.setVersion(Version.getProtocolVersion());
        req.setTwoWay(true);
        req.setData(request);
        DefaultFuture future = new DefaultFuture(channel, req, timeout);
        try {
            channel.send(req);
        } catch (RemotingException e) {
            future.cancel();
            throw e;
        }
        return future;
    }
}

• HeaderExchangeChannel的request()方法内部创建DefaultFuture并返回。
• DubboInvoker的get()方法执行的就是DefaultFuture的get()方法。
  
  

DefaultFuture#get

public class DefaultFuture implements ResponseFuture {

    private final Lock lock = new ReentrantLock();
    private final Condition done = lock.newCondition();

    public Object get(int timeout) throws RemotingException {
        if (timeout <= 0) {
            timeout = Constants.DEFAULT_TIMEOUT;
        }
        if (!isDone()) {
            long start = System.currentTimeMillis();
            lock.lock();
            try {
                while (!isDone()) {
                    done.await(timeout, TimeUnit.MILLISECONDS);
                    if (isDone() || System.currentTimeMillis() - start > timeout) {
                        break;
                    }
                }
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            } finally {
                lock.unlock();
            }
            if (!isDone()) {
                throw new TimeoutException(sent > 0, channel, getTimeoutMessage(false));
            }
        }
        return returnFromResponse();
    }

    private void doReceived(Response res) {
        lock.lock();
        try {
            response = res;
            if (done != null) {
                done.signal();
            }
        } finally {
            lock.unlock();
        }
        if (callback != null) {
            invokeCallback(callback);
        }
    }

    public boolean isDone() {
        return response != null;
    }

    private String getTimeoutMessage(boolean scan) {
        long nowTimestamp = System.currentTimeMillis();
        return (sent > 0 ? "Waiting server-side response timeout" : "Sending request timeout in client-side")
                + (scan ? " by scan timer" : "") + ". start time: "
                + (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date(start))) + ", end time: "
                + (new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS").format(new Date())) + ","
                + (sent > 0 ? " client elapsed: " + (sent - start)
                + " ms, server elapsed: " + (nowTimestamp - sent)
                : " elapsed: " + (nowTimestamp - start)) + " ms, timeout: "
                + timeout + " ms, request: " + request + ", channel: " + channel.getLocalAddress()
                + " -> " + channel.getRemoteAddress();
    }
}

• DefaultFuture内部的get()方法通过Condition的await()方法实现超时等待。
• 如果await()返回但是没有收到响应，即isDone()为false，抛出异常TimeoutException。
• 如果provider端成功响应，doReceived()设置response的值，则isDone()为true。
• 在isDone()返回false的情况会抛出TimeoutException异常，具体的异常信息通过getTimeoutMessage方法拼接。