Github user afine commented on a diff in the pull request:
https://github.com/apache/zookeeper/pull/205#discussion_r107973008
--- 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 --
nit: I think we generally prefer to explicitly state the access modifiers.
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