dubbo超时异常 荐

dubbo超时异常

在调用dubbo服务时经常看到如下错误：
Caused by: com.alibaba.dubbo.remoting.TimeoutException: Waiting server-side response timeout by scan timer.

源码分析

客户端调用远程服务时，本地会生成一个DefaultFuture，调用DefaultFuture.get()获取远程服务返回的结构,此方法获取锁，调用await方法，此时当前线程进入等待队列，此线程会有两种结果过：要么超时，抛出TimeOutException；如果被唤醒，则返回rpc的结果。
而这里的报错很明显是由于等待服务端返回结果时客户端超时异常，查看源码如下：

public class DefaultFuture implements ResponseFuture {

    private static final Logger                   logger = LoggerFactory.getLogger(DefaultFuture.class);

    private static final Map<Long, Channel>       CHANNELS   = new ConcurrentHashMap<Long, Channel>();

    private static final Map<Long, DefaultFuture> FUTURES   = new ConcurrentHashMap<Long, DefaultFuture>();

    // invoke id.
    private final long                            id;

    private final Channel                         channel;

    private final Request                         request;

    private final int                             timeout;

    private final Lock                            lock = new ReentrantLock();

    private final Condition                       done = lock.newCondition();

    private final long                            start = System.currentTimeMillis();

    private volatile long                         sent;

    private volatile Response                     response;

    private volatile ResponseCallback             callback;

    public DefaultFuture(Channel channel, Request request, int timeout){
        this.channel = channel;
        this.request = request;
        this.id = request.getId();
        this.timeout = timeout > 0 ? timeout : channel.getUrl().getPositiveParameter(Constants.TIMEOUT_KEY, Constants.DEFAULT_TIMEOUT);
        // put into waiting map.
        FUTURES.put(id, this);
        CHANNELS.put(id, channel);
    }

    public Object get() throws RemotingException {
        return get(timeout);
    }
    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();
    }
}

这里的超时时间设置的是1s

public static final int     DEFAULT_TIMEOUT                    = 1000;

解决方案

检查消费者配置查看是否配置总的超时时长，这里建议配置一个总的，我由于没配置导致使用的是默认配置使得超过1s就报错。

<dubbo:consumer timeout="5000" />

也可以在消费者端对每个服务自定义配置

<dubbo:reference interface="com.foo.BarService" timeout="2000"/>

这里也需要注意服务端也有一个超时时间

• 全局配置

<dubbo:provider  timeout="5000"/>

• 服务配置

<dubbo:provider interface="com.foo.BarService" timeout="5000">

当客户端timeout值>服务端timeout值，会出现超时日志，但是仍然可以获取到结果。客户端timeout超时抛出异常时，有一个线程RemotingInvocationTimeoutScan会自动清理对应超时的Future。