dubbo的FailbackClusterInvoker有什么作用

这篇文章主要介绍"dubbo的FailbackClusterInvoker有什么作用"，在日常操作中，相信很多人在dubbo的FailbackClusterInvoker有什么作用问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"dubbo的FailbackClusterInvoker有什么作用"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

序

本文主要研究一下dubbo的FailbackClusterInvoker

FailbackClusterInvoker

dubbo-2.7.3/dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/support/FailbackClusterInvoker.java

public class FailbackClusterInvoker extends AbstractClusterInvoker {    private static final Logger logger = LoggerFactory.getLogger(FailbackClusterInvoker.class);    private static final long RETRY_FAILED_PERIOD = 5;    private final int retries;    private final int failbackTasks;    private volatile Timer failTimer;    public FailbackClusterInvoker(Directory directory) {        super(directory);        int retriesConfig = getUrl().getParameter(RETRIES_KEY, DEFAULT_FAILBACK_TIMES);        if (retriesConfig <= 0) {            retriesConfig = DEFAULT_FAILBACK_TIMES;        }        int failbackTasksConfig = getUrl().getParameter(FAIL_BACK_TASKS_KEY, DEFAULT_FAILBACK_TASKS);        if (failbackTasksConfig <= 0) {            failbackTasksConfig = DEFAULT_FAILBACK_TASKS;        }        retries = retriesConfig;        failbackTasks = failbackTasksConfig;    }    private void addFailed(LoadBalance loadbalance, Invocation invocation, List> invokers, Invoker lastInvoker) {        if (failTimer == null) {            synchronized (this) {                if (failTimer == null) {                    failTimer = new HashedWheelTimer(                            new NamedThreadFactory("failback-cluster-timer", true),                            1,                            TimeUnit.SECONDS, 32, failbackTasks);                }            }        }        RetryTimerTask retryTimerTask = new RetryTimerTask(loadbalance, invocation, invokers, lastInvoker, retries, RETRY_FAILED_PERIOD);        try {            failTimer.newTimeout(retryTimerTask, RETRY_FAILED_PERIOD, TimeUnit.SECONDS);        } catch (Throwable e) {            logger.error("Failback background works error,invocation->" + invocation + ", exception: " + e.getMessage());        }    }    @Override    protected Result doInvoke(Invocation invocation, List> invokers, LoadBalance loadbalance) throws RpcException {        Invoker invoker = null;        try {            checkInvokers(invokers, invocation);            invoker = select(loadbalance, invocation, invokers, null);            return invoker.invoke(invocation);        } catch (Throwable e) {            logger.error("Failback to invoke method " + invocation.getMethodName() + ", wait for retry in background. Ignored exception: "                    + e.getMessage() + ", ", e);            addFailed(loadbalance, invocation, invokers, invoker);            return AsyncRpcResult.newDefaultAsyncResult(null, null, invocation); // ignore        }    }    @Override    public void destroy() {        super.destroy();        if (failTimer != null) {            failTimer.stop();        }    }    /**     * RetryTimerTask     */    private class RetryTimerTask implements TimerTask {        private final Invocation invocation;        private final LoadBalance loadbalance;        private final List> invokers;        private final int retries;        private final long tick;        private Invoker lastInvoker;        private int retryTimes = 0;        RetryTimerTask(LoadBalance loadbalance, Invocation invocation, List> invokers, Invoker lastInvoker, int retries, long tick) {            this.loadbalance = loadbalance;            this.invocation = invocation;            this.invokers = invokers;            this.retries = retries;            this.tick = tick;            this.lastInvoker=lastInvoker;        }        @Override        public void run(Timeout timeout) {            try {                Invoker retryInvoker = select(loadbalance, invocation, invokers, Collections.singletonList(lastInvoker));                lastInvoker = retryInvoker;                retryInvoker.invoke(invocation);            } catch (Throwable e) {                logger.error("Failed retry to invoke method " + invocation.getMethodName() + ", waiting again.", e);                if ((++retryTimes) >= retries) {                    logger.error("Failed retry times exceed threshold (" + retries + "), We have to abandon, invocation->" + invocation);                } else {                    rePut(timeout);                }            }        }        private void rePut(Timeout timeout) {            if (timeout == null) {                return;            }            Timer timer = timeout.timer();            if (timer.isStop() || timeout.isCancelled()) {                return;            }            timer.newTimeout(timeout.task(), tick, TimeUnit.SECONDS);        }    }}

• FailbackClusterInvoker的构造器初始化了retriesConfig、failbackTasksConfig；doInvoke方法在catch到Throwable的时候，会执行addFailed方法，该方法会往HashedWheelTimer注册一个RetryTimerTask，delay为5秒；RetryTimerTask的run方法首先会通过select方法选择一个retryInvoker，然后进行重试，catch到Throwable时会递增retryTimes，不超出限制时执行rePut方法，重新注册RetryTimerTask

FailbackClusterInvokerTest

dubbo-2.7.3/dubbo-cluster/src/test/java/org/apache/dubbo/rpc/cluster/support/FailbackClusterInvokerTest.java

@TestMethodOrder(MethodOrderer.OrderAnnotation.class)public class FailbackClusterInvokerTest {    List> invokers = new ArrayList>();    URL url = URL.valueOf("test://test:11/test?retries=2&failbacktasks=2");    Invoker invoker = mock(Invoker.class);    RpcInvocation invocation = new RpcInvocation();    Directory dic;    Result result = new AppResponse();    /**     * @throws java.lang.Exception     */    @BeforeEach    public void setUp() throws Exception {        dic = mock(Directory.class);        given(dic.getUrl()).willReturn(url);        given(dic.list(invocation)).willReturn(invokers);        given(dic.getInterface()).willReturn(FailbackClusterInvokerTest.class);        invocation.setMethodName("method1");        invokers.add(invoker);    }    @AfterEach    public void tearDown() {        dic = null;        invocation = new RpcInvocation();        invokers.clear();    }    private void resetInvokerToException() {        given(invoker.invoke(invocation)).willThrow(new RuntimeException());        given(invoker.getUrl()).willReturn(url);        given(invoker.getInterface()).willReturn(FailbackClusterInvokerTest.class);    }    private void resetInvokerToNoException() {        given(invoker.invoke(invocation)).willReturn(result);        given(invoker.getUrl()).willReturn(url);        given(invoker.getInterface()).willReturn(FailbackClusterInvokerTest.class);    }    @Test    @Order(1)    public void testInvokeException() {        resetInvokerToException();        FailbackClusterInvoker invoker = new FailbackClusterInvoker(                dic);        invoker.invoke(invocation);        Assertions.assertNull(RpcContext.getContext().getInvoker());        DubboAppender.clear();    }    @Test    @Order(2)    public void testInvokeNoException() {        resetInvokerToNoException();        FailbackClusterInvoker invoker = new FailbackClusterInvoker(                dic);        Result ret = invoker.invoke(invocation);        Assertions.assertSame(result, ret);    }    @Test    @Order(3)    public void testNoInvoke() {        dic = mock(Directory.class);        given(dic.getUrl()).willReturn(url);        given(dic.list(invocation)).willReturn(null);        given(dic.getInterface()).willReturn(FailbackClusterInvokerTest.class);        invocation.setMethodName("method1");        invokers.add(invoker);        resetInvokerToNoException();        FailbackClusterInvoker invoker = new FailbackClusterInvoker(                dic);        LogUtil.start();        DubboAppender.clear();        invoker.invoke(invocation);        assertEquals(1, LogUtil.findMessage("Failback to invoke"));        LogUtil.stop();    }    @Disabled    @Test    @Order(4)    public void testARetryFailed() throws Exception {        //Test retries and        resetInvokerToException();        FailbackClusterInvoker invoker = new FailbackClusterInvoker(                dic);        LogUtil.start();        DubboAppender.clear();        invoker.invoke(invocation);        invoker.invoke(invocation);        invoker.invoke(invocation);        Assertions.assertNull(RpcContext.getContext().getInvoker());//        invoker.retryFailed();// when retry the invoker which get from failed map already is not the mocked invoker,so        //Ensure that the main thread is online        CountDownLatch countDown = new CountDownLatch(1);        countDown.await(15000L, TimeUnit.MILLISECONDS);        LogUtil.stop();        Assertions.assertEquals(4, LogUtil.findMessage(Level.ERROR, "Failed retry to invoke method"), "must have four error message ");        Assertions.assertEquals(2, LogUtil.findMessage(Level.ERROR, "Failed retry times exceed threshold"), "must have two error message ");        Assertions.assertEquals(1, LogUtil.findMessage(Level.ERROR, "Failback background works error"), "must have one error message ");        // it can be invoke successfully    }}

• 这里使用mockito来mock了resetInvokerToException、resetInvokerToNoException

小结

FailbackClusterInvoker的构造器初始化了retriesConfig、failbackTasksConfig；doInvoke方法在catch到Throwable的时候，会执行addFailed方法，该方法会往HashedWheelTimer注册一个RetryTimerTask，delay为5秒；RetryTimerTask的run方法首先会通过select方法选择一个retryInvoker，然后进行重试，catch到Throwable时会递增retryTimes，不超出限制时执行rePut方法，重新注册RetryTimerTask

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