Dubbo ActiveLimitFilter限流

public class ActiveLimitFilter implements Filter, Filter.Listener {

    private static final String ACTIVE_LIMIT_FILTER_START_TIME = "active_limit_filter_start_time";

    @Override
    public Result invoke(Invoker<?> invoker, Invocation invocation) throws RpcException {
        URL url = invoker.getUrl();
        String methodName = invocation.getMethodName();
        // 最大并发量
        int max = invoker.getUrl().getMethodParameter(methodName, ACTIVES_KEY, 0);
        final RpcStatus rpcStatus = RpcStatus.getStatus(invoker.getUrl(), invocation.getMethodName());
        // 尝试给计数加一
        if (!RpcStatus.beginCount(url, methodName, max)) {
            // 获取计数失败
            long timeout = invoker.getUrl().getMethodParameter(invocation.getMethodName(), TIMEOUT_KEY, 0);
            long start = System.currentTimeMillis();
            long remain = timeout;
            synchronized (rpcStatus) {
                while (!RpcStatus.beginCount(url, methodName, max)) {
                    try {
                        rpcStatus.wait(remain);
                    } catch (InterruptedException e) {
                        // ignore
                    }
                    long elapsed = System.currentTimeMillis() - start;
                    // 等待剩余时间
                    remain = timeout - elapsed;
                    if (remain <= 0) {
                        // 等待超时
                        throw new RpcException(RpcException.LIMIT_EXCEEDED_EXCEPTION,
                                "Waiting concurrent invoke timeout in client-side for service:  " +
                                        invoker.getInterface().getName() + ", method: " + invocation.getMethodName() +
                                        ", elapsed: " + elapsed + ", timeout: " + timeout + ". concurrent invokes: " +
                                        rpcStatus.getActive() + ". max concurrent invoke limit: " + max);
                    }
                }
            }
        }

        invocation.put(ACTIVE_LIMIT_FILTER_START_TIME, System.currentTimeMillis());

        return invoker.invoke(invocation);
    }

    @Override
    public void onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation) {
        String methodName = invocation.getMethodName();
        URL url = invoker.getUrl();
        int max = invoker.getUrl().getMethodParameter(methodName, ACTIVES_KEY, 0);
        // 这里需要先计数减一再唤醒其他线程
        RpcStatus.endCount(url, methodName, getElapsed(invocation), true);
        notifyFinish(RpcStatus.getStatus(url, methodName), max);
    }

    @Override
    public void onError(Throwable t, Invoker<?> invoker, Invocation invocation) {
        String methodName = invocation.getMethodName();
        URL url = invoker.getUrl();
        int max = invoker.getUrl().getMethodParameter(methodName, ACTIVES_KEY, 0);

        if (t instanceof RpcException) {
            RpcException rpcException = (RpcException) t;
            if (rpcException.isLimitExceed()) {
                return;
            }
        }
        RpcStatus.endCount(url, methodName, getElapsed(invocation), false);
        notifyFinish(RpcStatus.getStatus(url, methodName), max);
    }

    private long getElapsed(Invocation invocation) {
        Object beginTime = invocation.get(ACTIVE_LIMIT_FILTER_START_TIME);
        return beginTime != null ? System.currentTimeMillis() - (Long) beginTime : 0;
    }

    private void notifyFinish(final RpcStatus rpcStatus, int max) {
        if (max > 0) {
            synchronized (rpcStatus) {
                rpcStatus.notifyAll();
            }
        }
    }
}

public class RpcStatus {

    /**
     * @param url
     */
    public static boolean beginCount(URL url, String methodName, int max) {
        max = (max <= 0) ? Integer.MAX_VALUE : max;
        RpcStatus appStatus = getStatus(url);
        RpcStatus methodStatus = getStatus(url, methodName);
        if (methodStatus.active.get() == Integer.MAX_VALUE) {
            return false;
        }
        // 这里的CAS写法值得学习
        for (int i; ; ) {
            i = methodStatus.active.get();

            if (i == Integer.MAX_VALUE || i + 1 > max) {
                return false;
            }

            if (methodStatus.active.compareAndSet(i, i + 1)) {
                break;
            }
        }

        appStatus.active.incrementAndGet();

        return true;
    }


    private static void endCount(RpcStatus status, long elapsed, boolean succeeded) {
        status.active.decrementAndGet();
        status.total.incrementAndGet();
        status.totalElapsed.addAndGet(elapsed);

        if (status.maxElapsed.get() < elapsed) {
            status.maxElapsed.set(elapsed);
        }

        if (succeeded) {
            if (status.succeededMaxElapsed.get() < elapsed) {
                status.succeededMaxElapsed.set(elapsed);
            }

        } else {
            status.failed.incrementAndGet();
            status.failedElapsed.addAndGet(elapsed);
            if (status.failedMaxElapsed.get() < elapsed) {
                status.failedMaxElapsed.set(elapsed);
            }
        }
    }


}