content: /*
   * Copyright 1999-2018 Alibaba Group Holding Ltd.
   *
   * Licensed 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 com.alibaba.csp.sentinel.eagleeye;
  
  import java.util.concurrent.atomic.AtomicLong;
  
  class TokenBucket {
  
      private final long maxTokens;
  
      private final long intervalMillis;
  
      private volatile long nextUpdate;
  
      private AtomicLong tokens;
  
      public TokenBucket(long maxTokens, long intervalMillis) {
          if (maxTokens <= 0) {
              throw new IllegalArgumentException("maxTokens should > 0, but given: " + maxTokens);
          }
          if (intervalMillis < 1000) {
              throw new IllegalArgumentException("intervalMillis should be at least 1000, but given: " + intervalMillis);
          }
          this.maxTokens = maxTokens;
          this.intervalMillis = intervalMillis;
          this.nextUpdate = System.currentTimeMillis() / 1000 * 1000 + intervalMillis;
          this.tokens = new AtomicLong(maxTokens);
      }
  
      public boolean accept(long now) {
          long currTokens;
          if (now > nextUpdate) {
              currTokens = tokens.get();
              if (tokens.compareAndSet(currTokens, maxTokens)) {
                  nextUpdate = System.currentTimeMillis() / 1000 * 1000 + intervalMillis;
              }
          }
  
          do {
              currTokens = tokens.get();
          } while (currTokens > 0 && !tokens.compareAndSet(currTokens, currTokens - 1));
  
          return currTokens > 0;
      }
  }
  