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.server.datanode.fsdataset;
019    
020    import java.io.IOException;
021    import java.util.List;
022    
023    import org.apache.commons.logging.Log;
024    import org.apache.commons.logging.LogFactory;
025    import org.apache.hadoop.hdfs.StorageType;
026    import org.apache.hadoop.util.DiskChecker.DiskOutOfSpaceException;
027    
028    /**
029     * Choose volumes in round-robin order.
030     */
031    public class RoundRobinVolumeChoosingPolicy<V extends FsVolumeSpi>
032        implements VolumeChoosingPolicy<V> {
033      public static final Log LOG = LogFactory.getLog(RoundRobinVolumeChoosingPolicy.class);
034    
035      private int curVolume = 0;
036    
037      @Override
038      public synchronized V chooseVolume(final List<V> volumes, long blockSize)
039          throws IOException {
040    
041        if(volumes.size() < 1) {
042          throw new DiskOutOfSpaceException("No more available volumes");
043        }
044        
045        // since volumes could've been removed because of the failure
046        // make sure we are not out of bounds
047        if(curVolume >= volumes.size()) {
048          curVolume = 0;
049        }
050        
051        int startVolume = curVolume;
052        long maxAvailable = 0;
053        
054        while (true) {
055          final V volume = volumes.get(curVolume);
056          curVolume = (curVolume + 1) % volumes.size();
057          long availableVolumeSize = volume.getAvailable();
058          if (availableVolumeSize > blockSize) {
059            return volume;
060          }
061          
062          if (availableVolumeSize > maxAvailable) {
063            maxAvailable = availableVolumeSize;
064          }
065          
066          if (curVolume == startVolume) {
067            throw new DiskOutOfSpaceException("Out of space: "
068                + "The volume with the most available space (=" + maxAvailable
069                + " B) is less than the block size (=" + blockSize + " B).");
070          }
071        }
072      }
073    }