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本文主要研究一下dubbo的ExecuteLimitFilter

ExecuteLimitFilter

dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/filter/ExecuteLimitFilter.java

public class ExecuteLimitFilter extends ListenableFilter {

    private static final String EXECUTELIMIT_FILTER_START_TIME = "execugtelimit_filter_start_time";

    public ExecuteLimitFilter() {
        super.listener = new ExecuteLimitListener();
    }

    @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("Failed to invoke method " + invocation.getMethodName() + " in provider " +
                    url + ", cause: The service using threads greater than <dubbo:service executes=\"" + 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);
            }
        }
    }

    static class ExecuteLimitListener implements Listener {
        @Override
        public void onResponse(Result appResponse, Invoker<?> invoker, Invocation invocation) {
            RpcStatus.endCount(invoker.getUrl(), invocation.getMethodName(), getElapsed(invocation), true);
        }

        @Override
        public void onError(Throwable t, Invoker<?> invoker, Invocation invocation) {
            RpcStatus.endCount(invoker.getUrl(), invocation.getMethodName(), getElapsed(invocation), false);
        }

        private long getElapsed(Invocation invocation) {
            String beginTime = invocation.getAttachment(EXECUTELIMIT_FILTER_START_TIME);
            return StringUtils.isNotEmpty(beginTime) ? System.currentTimeMillis() - Long.parseLong(beginTime) : 0;
        }
    }
}

• ExecuteLimitFilter继承了ListenableFilter，其构造器初始化的listener为ExecuteLimitListener
• invoke方法先调用RpcStatus.beginCount方法来判断是否可以通过，不通过则抛出RpcException，通过则记录开始执行的时间，然后执行invoker.invoke方法，执行结束时会回调Listener的onResponse或onError方法
• ExecuteLimitListener的onResponse及onError方法均会调用RpcStatus.endCount；而该方法会通过getElapsed方法取出execugtelimit_filter_start_time值，计算执行耗时

RpcStatus

dubbo-2.7.2/dubbo-rpc/dubbo-rpc-api/src/main/java/org/apache/dubbo/rpc/RpcStatus.java

public class RpcStatus {

    private static final ConcurrentMap<String, RpcStatus> SERVICE_STATISTICS = new ConcurrentHashMap<String, RpcStatus>();

    private static final ConcurrentMap<String, ConcurrentMap<String, RpcStatus>> METHOD_STATISTICS = new ConcurrentHashMap<String, ConcurrentMap<String, RpcStatus>>();
    private final ConcurrentMap<String, Object> values = new ConcurrentHashMap<String, Object>();
    private final AtomicInteger active = new AtomicInteger();
    private final AtomicLong total = new AtomicLong();
    private final AtomicInteger failed = new AtomicInteger();
    private final AtomicLong totalElapsed = new AtomicLong();
    private final AtomicLong failedElapsed = new AtomicLong();
    private final AtomicLong maxElapsed = new AtomicLong();
    private final AtomicLong failedMaxElapsed = new AtomicLong();
    private final AtomicLong succeededMaxElapsed = new AtomicLong();

    //......

    public static void beginCount(URL url, String methodName) {
        beginCount(url, methodName, Integer.MAX_VALUE);
    }

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

    /**
     * @param url
     * @param elapsed
     * @param succeeded
     */
    public static void endCount(URL url, String methodName, long elapsed, boolean succeeded) {
        endCount(getStatus(url), elapsed, succeeded);
        endCount(getStatus(url, methodName), elapsed, succeeded);
    }

    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);
            }
        }
    }

    //......
}

• RpcStatus的beginCount方法会递增methodStatus.active，然后判断是否大于max值，超出则返回false并递减methodStatus.active；小于等于则递增appStatus.active；endCount方法会递减status.active，递增status.total，然后根据成功与否更新status.succeededMaxElapsed或status.failed、status.failedElapsed、status.failedMaxElapsed

小结

• ExecuteLimitFilter继承了ListenableFilter，其构造器初始化的listener为ExecuteLimitListener
• ExecuteLimitFilter的invoke方法先调用RpcStatus.beginCount方法来判断是否可以通过，不通过则抛出RpcException，通过则记录开始执行的时间，然后执行invoker.invoke方法，执行结束时会回调Listener的onResponse或onError方法
• ExecuteLimitListener的onResponse及onError方法均会调用RpcStatus.endCount；而该方法会通过getElapsed方法取出execugtelimit_filter_start_time值，计算执行耗时

doc

• ExecuteLimitFilter