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    import static org.apache.hadoop.util.Time.monotonicNow;
021    
022    /** 
023     * a class to throttle the data transfers.
024     * This class is thread safe. It can be shared by multiple threads.
025     * The parameter bandwidthPerSec specifies the total bandwidth shared by
026     * threads.
027     */
028    public class DataTransferThrottler {
029      private long period;          // period over which bw is imposed
030      private long periodExtension; // Max period over which bw accumulates.
031      private long bytesPerPeriod;  // total number of bytes can be sent in each period
032      private long curPeriodStart;  // current period starting time
033      private long curReserve;      // remaining bytes can be sent in the period
034      private long bytesAlreadyUsed;
035    
036      /** Constructor 
037       * @param bandwidthPerSec bandwidth allowed in bytes per second. 
038       */
039      public DataTransferThrottler(long bandwidthPerSec) {
040        this(500, bandwidthPerSec);  // by default throttling period is 500ms 
041      }
042    
043      /**
044       * Constructor
045       * @param period in milliseconds. Bandwidth is enforced over this
046       *        period.
047       * @param bandwidthPerSec bandwidth allowed in bytes per second. 
048       */
049      public DataTransferThrottler(long period, long bandwidthPerSec) {
050        this.curPeriodStart = monotonicNow();
051        this.period = period;
052        this.curReserve = this.bytesPerPeriod = bandwidthPerSec*period/1000;
053        this.periodExtension = period*3;
054      }
055    
056      /**
057       * @return current throttle bandwidth in bytes per second.
058       */
059      public synchronized long getBandwidth() {
060        return bytesPerPeriod*1000/period;
061      }
062      
063      /**
064       * Sets throttle bandwidth. This takes affect latest by the end of current
065       * period.
066       * 
067       * @param bytesPerSecond 
068       */
069      public synchronized void setBandwidth(long bytesPerSecond) {
070        if ( bytesPerSecond <= 0 ) {
071          throw new IllegalArgumentException("" + bytesPerSecond);
072        }
073        bytesPerPeriod = bytesPerSecond*period/1000;
074      }
075      
076      /** Given the numOfBytes sent/received since last time throttle was called,
077       * make the current thread sleep if I/O rate is too fast
078       * compared to the given bandwidth.
079       *
080       * @param numOfBytes
081       *     number of bytes sent/received since last time throttle was called
082       */
083      public synchronized void throttle(long numOfBytes) {
084        if ( numOfBytes <= 0 ) {
085          return;
086        }
087    
088        curReserve -= numOfBytes;
089        bytesAlreadyUsed += numOfBytes;
090    
091        while (curReserve <= 0) {
092          long now = monotonicNow();
093          long curPeriodEnd = curPeriodStart + period;
094    
095          if ( now < curPeriodEnd ) {
096            // Wait for next period so that curReserve can be increased.
097            try {
098              wait( curPeriodEnd - now );
099            } catch (InterruptedException e) {
100              // Abort throttle and reset interrupted status to make sure other
101              // interrupt handling higher in the call stack executes.
102              Thread.currentThread().interrupt();
103              break;
104            }
105          } else if ( now <  (curPeriodStart + periodExtension)) {
106            curPeriodStart = curPeriodEnd;
107            curReserve += bytesPerPeriod;
108          } else {
109            // discard the prev period. Throttler might not have
110            // been used for a long time.
111            curPeriodStart = now;
112            curReserve = bytesPerPeriod - bytesAlreadyUsed;
113          }
114        }
115    
116        bytesAlreadyUsed -= numOfBytes;
117      }
118    }