【Dubbo系列】Dubbo控制并发数和限流

ExecuteLimitFilter

在Service注解上设置executes可以控制并发数

@Service(timeout = 10000,executes = 10)

ExecuteLimitFilter#invoke，核心的处理逻辑。

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

        invocation.setAttachment(EXECUTELIMIT_FILTER_START_TIME, String.valueOf(System.currentTimeMillis()));
        try {
            return invoker.invoke(invocation);
        } catch (Throwable t) {
            if (t instanceof RuntimeException) {
                throw (RuntimeException) t;
            } else {
                throw new RpcException("unexpected exception when ExecuteLimitFilter", t);
            }
        }
    }

RpcStatus#beginCount(URL, String, int)，根据url和方法获取RpcStatus

    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;
        }
        if (methodStatus.active.incrementAndGet() > max) {
            methodStatus.active.decrementAndGet();
            return false;
        } else {
            appStatus.active.incrementAndGet();
            return true;
        }
    }

DefaultTPSLimiter

DefaultTPSLimiter，获取StatItem，根据statItem.isAllowable()的处理结果来控制。

public class DefaultTPSLimiter implements TPSLimiter {

    private final ConcurrentMap<String, StatItem> stats = new ConcurrentHashMap<String, StatItem>();

    @Override
    public boolean isAllowable(URL url, Invocation invocation) {
        int rate = url.getParameter(TPS_LIMIT_RATE_KEY, -1);
        long interval = url.getParameter(TPS_LIMIT_INTERVAL_KEY, DEFAULT_TPS_LIMIT_INTERVAL);
        String serviceKey = url.getServiceKey();
        if (rate > 0) {
            StatItem statItem = stats.get(serviceKey);
            if (statItem == null) {
                stats.putIfAbsent(serviceKey, new StatItem(serviceKey, rate, interval));
                statItem = stats.get(serviceKey);
            } else {
                //rate or interval has changed, rebuild
                if (statItem.getRate() != rate || statItem.getInterval() != interval) {
                    stats.put(serviceKey, new StatItem(serviceKey, rate, interval));
                    statItem = stats.get(serviceKey);
                }
            }
            return statItem.isAllowable();
        } else {
            StatItem statItem = stats.get(serviceKey);
            if (statItem != null) {
                stats.remove(serviceKey);
            }
        }

        return true;
    }

}

StatItem#isAllowable，如果超过间隔，重置计数。

    public boolean isAllowable() {
        long now = System.currentTimeMillis();
        if (now > lastResetTime + interval) {
            token = buildLongAdder(rate);
            lastResetTime = now;
        }

        if (token.sum() < 0) {
            return false;
        }
        token.decrement();
        return true;
    }