001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    package org.apache.hadoop.hdfs.util;
019    
020    /** 
021     * a class to throttle the data transfers.
022     * This class is thread safe. It can be shared by multiple threads.
023     * The parameter bandwidthPerSec specifies the total bandwidth shared by
024     * threads.
025     */
026    public class DataTransferThrottler {
027      private long period;          // period over which bw is imposed
028      private long periodExtension; // Max period over which bw accumulates.
029      private long bytesPerPeriod; // total number of bytes can be sent in each period
030      private long curPeriodStart; // current period starting time
031      private long curReserve;     // remaining bytes can be sent in the period
032      private long bytesAlreadyUsed;
033    
034      /** Constructor 
035       * @param bandwidthPerSec bandwidth allowed in bytes per second. 
036       */
037      public DataTransferThrottler(long bandwidthPerSec) {
038        this(500, bandwidthPerSec);  // by default throttling period is 500ms 
039      }
040    
041      /**
042       * Constructor
043       * @param period in milliseconds. Bandwidth is enforced over this
044       *        period.
045       * @param bandwidthPerSec bandwidth allowed in bytes per second. 
046       */
047      public DataTransferThrottler(long period, long bandwidthPerSec) {
048        this.curPeriodStart = System.currentTimeMillis();
049        this.period = period;
050        this.curReserve = this.bytesPerPeriod = bandwidthPerSec*period/1000;
051        this.periodExtension = period*3;
052      }
053    
054      /**
055       * @return current throttle bandwidth in bytes per second.
056       */
057      public synchronized long getBandwidth() {
058        return bytesPerPeriod*1000/period;
059      }
060      
061      /**
062       * Sets throttle bandwidth. This takes affect latest by the end of current
063       * period.
064       * 
065       * @param bytesPerSecond 
066       */
067      public synchronized void setBandwidth(long bytesPerSecond) {
068        if ( bytesPerSecond <= 0 ) {
069          throw new IllegalArgumentException("" + bytesPerSecond);
070        }
071        bytesPerPeriod = bytesPerSecond*period/1000;
072      }
073      
074      /** Given the numOfBytes sent/received since last time throttle was called,
075       * make the current thread sleep if I/O rate is too fast
076       * compared to the given bandwidth.
077       *
078       * @param numOfBytes
079       *     number of bytes sent/received since last time throttle was called
080       */
081      public synchronized void throttle(long numOfBytes) {
082        if ( numOfBytes <= 0 ) {
083          return;
084        }
085    
086        curReserve -= numOfBytes;
087        bytesAlreadyUsed += numOfBytes;
088    
089        while (curReserve <= 0) {
090          long now = System.currentTimeMillis();
091          long curPeriodEnd = curPeriodStart + period;
092    
093          if ( now < curPeriodEnd ) {
094            // Wait for next period so that curReserve can be increased.
095            try {
096              wait( curPeriodEnd - now );
097            } catch (InterruptedException ignored) {}
098          } else if ( now <  (curPeriodStart + periodExtension)) {
099            curPeriodStart = curPeriodEnd;
100            curReserve += bytesPerPeriod;
101          } else {
102            // discard the prev period. Throttler might not have
103            // been used for a long time.
104            curPeriodStart = now;
105            curReserve = bytesPerPeriod - bytesAlreadyUsed;
106          }
107        }
108    
109        bytesAlreadyUsed -= numOfBytes;
110      }
111    }