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From eribeiro <...@git.apache.org>
Subject [GitHub] zookeeper pull request #205: ZOOKEEPER-2736 Add a connection rate limiter
Date Fri, 24 Mar 2017 22:21:19 GMT
Github user eribeiro commented on a diff in the pull request:

    https://github.com/apache/zookeeper/pull/205#discussion_r108010303
  
    --- Diff: src/java/main/org/apache/zookeeper/common/TokenBucket.java ---
    @@ -0,0 +1,88 @@
    +/**
    +* Licensed to the Apache Software Foundation (ASF) under one
    +* or more contributor license agreements.  See the NOTICE file
    +* distributed with this work for additional information
    +* regarding copyright ownership.  The ASF licenses this file
    +* to you under the Apache License, Version 2.0 (the
    +* "License"); you may not use this file except in compliance
    +* with the License.  You may obtain a copy of the License at
    +*
    +*     http://www.apache.org/licenses/LICENSE-2.0
    +*
    +* Unless required by applicable law or agreed to in writing, software
    +* distributed under the License is distributed on an "AS IS" BASIS,
    +* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    +* See the License for the specific language governing permissions and
    +* limitations under the License.
    +*/
    +package org.apache.zookeeper.common;
    +
    +import java.util.concurrent.TimeUnit;
    +import java.util.concurrent.atomic.AtomicLong;
    +
    +/**
    + * Simple rate limiter based on a token bucket.
    +  */
    +public class TokenBucket implements RateLimiter {
    +
    +    // VisibleForTesting
    +    long refreshPeriodNanos = TimeUnit.SECONDS.toNanos(1L);
    +    // VisibleForTesting
    +    volatile long nextRefillTime;
    +    private AtomicLong tokens;
    +    private long capacity;
    +    private long tokensPerPeriod;
    +
    +    public TokenBucket() { }
    +
    +    // VisibleForTesting
    +    public TokenBucket(long capacity, long tokensPerSecond, long initialTokens) {
    +        this.tokens = new AtomicLong(initialTokens);
    +        this.capacity = Math.max(capacity, tokensPerSecond);
    +        this.tokensPerPeriod = tokensPerSecond;
    +        this.nextRefillTime = System.nanoTime() + refreshPeriodNanos;
    +    }
    +
    +    @Override
    +    public boolean tryAquire() {
    +        refill();
    +        long current = tokens.get();
    +        while (current > 0) {
    +            if (tokens.compareAndSet(current, current - 1)) {
    +                return true;
    +            }
    +            current = tokens.get();
    +        }
    +        return false;
    +    }
    +
    +    private void refill() {
    +        long currentTime = System.nanoTime();
    +        if (currentTime >= nextRefillTime) {
    +            synchronized (this) {
    +                if (currentTime >= nextRefillTime) {
    +                    long elapsedNanos = currentTime - nextRefillTime + refreshPeriodNanos;
    +                    long elapsedPeriods = elapsedNanos / refreshPeriodNanos;
    +                    long newTokens = elapsedPeriods * tokensPerPeriod;
    +                    tokens.set(Math.min(capacity, tokens.get() + newTokens));
    +                    nextRefillTime = currentTime + refreshPeriodNanos - (elapsedNanos
% refreshPeriodNanos);
    +                }
    +            }
    +        }
    +    }
    +
    +    // VisibleForTesting
    +    long getTokenCount() {
    --- End diff --
    
    +1.


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