SpringCloud Alibaba系列——11Dubbo的负载均衡原理

@Overrideprotected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation                                  invocation) {    // Number of invokers    int length = invokers.size();    //判断是否需要权重随机    if (!needWeightLoadBalance(invokers,invocation)){        return invokers.get(ThreadLocalRandom.current().nextInt(length));    }    // Every invoker has the same weight?    boolean sameWeight = true;    // the maxWeight of every invokers, the minWeight = 0 or the maxWeight of the last invoker    int[] weights = new int[length];    // The sum of weights    int totalWeight = 0;    for (int i = 0; i < length; i++) {        //获取每一个invoker的权重        int weight = getWeight(invokers.get(i), invocation);        // Sum        totalWeight += weight;        // save for later use        weights[i] = totalWeight;        //如果各节点权重是不相同的        if (sameWeight && totalWeight != weight * (i + 1)) {            sameWeight = false;        }    }    if (totalWeight > 0 && !sameWeight) {        // If (not every invoker has the same weight & at least one invoker's weight>0),select randomly based on totalWeight.        int offset = ThreadLocalRandom.current().nextInt(totalWeight);        // Return a invoker based on the random value.        for (int i = 0; i < length; i++) {            //判断offset落在哪一个权重区间            if (offset < weights[i]) {                return invokers.get(i);            }        }    }    //如果权重相同，则是真随机    // If all invokers have the same weight value or totalWeight=0, return evenly.    return invokers.get(ThreadLocalRandom.current().nextInt(length));}
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@Overrideprotected <T> Invoker<T> doSelect(List<Invoker<T>> invokers, URL url, Invocation                                  invocation) {    String key = invokers.get(0).getUrl().getServiceKey() + "." +        invocation.getMethodName();    ConcurrentMap<String, WeightedRoundRobin> map = methodWeightMap.computeIfAbsent(key, k                                                                                    -> new ConcurrentHashMap<>());    int totalWeight = 0;    long maxCurrent = Long.MIN_VALUE;    long now = System.currentTimeMillis();    Invoker<T> selectedInvoker = null;    WeightedRoundRobin selectedWRR = null;    for (Invoker<T> invoker : invokers) {        String identifyString = invoker.getUrl().toIdentityString();        int weight = getWeight(invoker, invocation);        WeightedRoundRobin weightedRoundRobin = map.computeIfAbsent(identifyString, k -> {            WeightedRoundRobin wrr = new WeightedRoundRobin();            wrr.setWeight(weight);            return wrr;        });        if (weight != weightedRoundRobin.getWeight()) {            //weight changed            weightedRoundRobin.setWeight(weight);        }        long cur = weightedRoundRobin.increaseCurrent();        weightedRoundRobin.setLastUpdate(now);        if (cur > maxCurrent) {            maxCurrent = cur;            selectedInvoker = invoker;            selectedWRR = weightedRoundRobin;        }        totalWeight += weight;    }    if (invokers.size() != map.size()) {        map.entrySet().removeIf(item -> now - item.getValue().getLastUpdate() >                                RECYCLE_PERIOD);    }    if (selectedInvoker != null) {        selectedWRR.sel(totalWeight);        return selectedInvoker;    }    // should not happen here    return invokers.get(0);}
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result = doMockInvoke(invocation, null);
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private Result doMockInvoke(Invocation invocation, RpcException e) {    Result result = null;    Invoker<T> minvoker;    //选择一个MockInvoker的实例，这里是选不到的    List<Invoker<T>> mockInvokers = selectMockInvoker(invocation);    if (CollectionUtils.isEmpty(mockInvokers)) {        //所以代码会走这里，创建一个MockInvoker对象        minvoker = (Invoker<T>) new MockInvoker(getUrl(), directory.getInterface());    } else {        minvoker = mockInvokers.get(0);    }    try {        //调用mock的实现类方法        result = minvoker.invoke(invocation);    } catch (RpcException me) {        if (me.isBiz()) {            result = AsyncRpcResult.newDefaultAsyncResult(me.getCause(), invocation);        } else {            throw new RpcException(me.getCode(), getMockExceptionMessage(e, me),                                   me.getCause());        }    } catch (Throwable me) {        throw new RpcException(getMockExceptionMessage(e, me), me.getCause());    }    return result;}
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@Overridepublic Result invoke(Invocation invocation) throws RpcException {    if (invocation instanceof RpcInvocation) {        ((RpcInvocation) invocation).setInvoker(this);    }    String mock = null;    if (getUrl().hasMethodParameter(invocation.getMethodName())) {        mock = getUrl().getParameter(invocation.getMethodName() + "." + MOCK_KEY);    }    if (StringUtils.isBlank(mock)) {        //获取配置的mock的属性值        mock = getUrl().getParameter(MOCK_KEY);    }    if (StringUtils.isBlank(mock)) {        throw new RpcException(new IllegalAccessException("mock can not be null. url :" +url));    }    //把force:前缀去掉，获取后面的值    mock = normalizeMock(URL.decode(mock));    //如果是return开头    if (mock.startsWith(RETURN_PREFIX)) {        //获取return后面的值        mock = mock.substring(RETURN_PREFIX.length()).trim();        try {            //获取返回值类型            Type[] returnTypes = RpcUtils.getReturnTypes(invocation);            //把return后面的值包装成返回值类型            Object value = parseMockValue(mock, returnTypes);            //注解把结果返回没走后端rpc调用            return AsyncRpcResult.newDefaultAsyncResult(value, invocation);        } catch (Exception ew) {            throw new RpcException("mock return invoke error. method :" +                                   invocation.getMethodName()                                   + ", mock:" + mock + ", url: " + url, ew);        }        //如果是throw    } else if (mock.startsWith(THROW_PREFIX)) {        mock = mock.substring(THROW_PREFIX.length()).trim();        if (StringUtils.isBlank(mock)) {            throw new RpcException("mocked exception for service degradation.");        } else { // user customized class            //获取异常实例            Throwable t = getThrowable(mock);            //直接往上抛异常            throw new RpcException(RpcException.BIZ_EXCEPTION, t);        }    } else { //impl mock        //mock实现类的方式        try {            Invoker<T> invoker = getInvoker(mock);            //调用mock实例            return invoker.invoke(invocation);        } catch (Throwable t) {            throw new RpcException("Failed to create mock implementation class " + mock,t);        }    }}
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public static String normalizeMock(String mock) {    if (mock == null) {        return mock;    }    mock = mock.trim();    if (mock.length() == 0) {        return mock;    }    //如果是只有一个return 则加上一个return null    if (RETURN_KEY.equalsIgnoreCase(mock)) {        return RETURN_PREFIX + "null";    }    if (ConfigUtils.isDefault(mock) || "fail".equalsIgnoreCase(mock) ||        "force".equalsIgnoreCase(mock)) {        return "default";    }    if (mock.startsWith(FAIL_PREFIX)) {        mock = mock.substring(FAIL_PREFIX.length()).trim();    }    //把force:去掉    if (mock.startsWith(FORCE_PREFIX)) {        mock = mock.substring(FORCE_PREFIX.length()).trim();    }    if (mock.startsWith(RETURN_PREFIX) || mock.startsWith(THROW_PREFIX)) {        mock = mock.replace('`', '"');    }    return mock;}
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public static Object parseMockValue(String mock, Type[] returnTypes) throws Exception {    Object value = null;    if ("empty".equals(mock)) {        value = ReflectUtils.getEmptyObject(returnTypes != null && returnTypes.length > 0 ?                                            (Class<?>) returnTypes[0] : null);    } else if ("null".equals(mock)) {        value = null;    } else if ("true".equals(mock)) {        value = true;    } else if ("false".equals(mock)) {        value = false;    } else if (mock.length() >= 2 && (mock.startsWith("\"") && mock.endsWith("\"")                                      || mock.startsWith("\'") && mock.endsWith("\'"))) {        value = mock.subSequence(1, mock.length() - 1);    } else if (returnTypes != null && returnTypes.length > 0 && returnTypes[0] ==               String.class) {        value = mock;    } else if (StringUtils.isNumeric(mock, false)) {        value = JSON.parse(mock);    } else if (mock.startsWith("{")) {        value = JSON.parseObject(mock, Map.class);    } else if (mock.startsWith("[")) {        value = JSON.parseObject(mock, List.class);    } else {        value = mock;    }    if (ArrayUtils.isNotEmpty(returnTypes)) {        value = PojoUtils.realize(value, (Class<?>) returnTypes[0], returnTypes.length > 1                                  ? returnTypes[1] : null);    }    return value;}
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