25.Dubbo并发控制

消费端控制并发个数

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此设置针对GreetingService接口中的所有方法，每个方法最多同时并发请求10个。

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针对于特定的方法设置

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在服务消费端，具体进行并发控制的是ProtocolFilterWrapper类创建的Filter链中的ActivieLimitFilter()方法

public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        URL url = invoker.getUrl();
        String methodName = invocation.getMethodName();
        int max = invoker.getUrl().getMethodParameter(methodName, Constants.ACTIVES_KEY, 0);
        RpcStatus count = RpcStatus.getStatus(invoker.getUrl(), invocation.getMethodName());
        if (!count.beginCount(url, methodName, max)) {
            long timeout = invoker.getUrl().getMethodParameter(invocation.getMethodName(), Constants.TIMEOUT_KEY, 0);
            long start = System.currentTimeMillis();
            long remain = timeout;
            synchronized (count) {
                while (!count.beginCount(url, methodName, max)) {
                    try {
                        count.wait(remain);
                    } catch (InterruptedException e) {
                        // ignore
                    }
                    long elapsed = System.currentTimeMillis() - start;
                    remain = timeout - elapsed;
                    if (remain <= 0) {
                        throw new RpcException("Waiting concurrent invoke timeout in client-side for service:  "
                                + invoker.getInterface().getName() + ", method: "
                                + invocation.getMethodName() + ", elapsed: " + elapsed
                                + ", timeout: " + timeout + ". concurrent invokes: " + count.getActive()
                                + ". max concurrent invoke limit: " + max);
                    }
                }
            }
        }

        boolean isSuccess = true;
        long begin = System.currentTimeMillis();
        try {
            return invoker.invoke(invocation);
        } catch (RuntimeException t) {
            isSuccess = false;
            throw t;
        } finally {
            count.endCount(url, methodName, System.currentTimeMillis() - begin, isSuccess);
            if (max > 0) {
                synchronized (count) {
                    count.notifyAll();
                }
            }
        }
    }

超出的请求将会在超时后抛出异常并被丢弃。

服务端控制并发个数

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具体进行并发控制的是ProtocolFilterWrapper类创建的Filter链中的ExecuteLimitFilter()

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 public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        URL url = invoker.getUrl();
        String methodName = invocation.getMethodName();
        int max = url.getMethodParameter(methodName, Constants.EXECUTES_KEY, 0);
        if (!RpcStatus.beginCount(url, methodName, max)) {
            throw new RpcException("Failed to invoke method " + invocation.getMethodName() + " in provider " +
                    url + ", cause: The service using threads greater than <dubbo:service executes=\"" + max +
                    "\" /> limited.");
        }

        long begin = System.currentTimeMillis();
        boolean isSuccess = true;
        try {
            return invoker.invoke(invocation);
        } catch (Throwable t) {
            isSuccess = false;
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new RpcException("unexpected exception when ExecuteLimitFilter", t);
            }
        } finally {
            RpcStatus.endCount(url, methodName, System.currentTimeMillis() - begin, isSuccess);
        }
    }

与消费端类似，通过RpcStatus来统计接口请求次数并作出判断。