hbase-server/src/main/java/org/apache/hadoop/hbase/io/FSDataInputStreamWrapper.java - hbase - Git at Google

 /**
  * 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.hadoop.hbase.io;

 import java.io.Closeable;
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.concurrent.atomic.AtomicInteger;

 import org.apache.commons.io.IOUtils;
 import org.apache.hadoop.fs.CanUnbuffer;
 import org.apache.hadoop.fs.FSDataInputStream;
 import org.apache.hadoop.fs.FileSystem;
 import org.apache.hadoop.fs.Path;
 import org.apache.hadoop.hbase.fs.HFileSystem;
 import org.apache.hadoop.hdfs.client.HdfsDataInputStream;
 import org.apache.yetus.audience.InterfaceAudience;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;

 /**
  * Wrapper for input stream(s) that takes care of the interaction of FS and HBase checksums,
  * as well as closing streams. Initialization is not thread-safe, but normal operation is;
  * see method comments.
  */
 @InterfaceAudience.Private
 public class FSDataInputStreamWrapper implements Closeable {
   private static final Logger LOG = LoggerFactory.getLogger(FSDataInputStreamWrapper.class);
   private static final boolean isLogTraceEnabled = LOG.isTraceEnabled();

   private final HFileSystem hfs;
   private final Path path;
   private final FileLink link;
   private final boolean doCloseStreams;
   private final boolean dropBehind;
   private final long readahead;

   /** Two stream handles, one with and one without FS-level checksum.
    * HDFS checksum setting is on FS level, not single read level, so you have to keep two
    * FS objects and two handles open to interleave different reads freely, which is very sad.
    * This is what we do:
    * 1) First, we need to read the trailer of HFile to determine checksum parameters.
    *  We always use FS checksum to do that, so ctor opens {@link #stream}.
    * 2.1) After that, if HBase checksum is not used, we'd just always use {@link #stream};
    * 2.2) If HBase checksum can be used, we'll open {@link #streamNoFsChecksum},
    *  and close {@link #stream}. User MUST call prepareForBlockReader for that to happen;
    *  if they don't, (2.1) will be the default.
    * 3) The users can call {@link #shouldUseHBaseChecksum()}, and pass its result to
    *  {@link #getStream(boolean)} to get stream (if Java had out/pointer params we could
    *  return both in one call). This stream is guaranteed to be set.
    * 4) The first time HBase checksum fails, one would call {@link #fallbackToFsChecksum(int)}.
    * That will take lock, and open {@link #stream}. While this is going on, others will
    * continue to use the old stream; if they also want to fall back, they'll also call
    * {@link #fallbackToFsChecksum(int)}, and block until {@link #stream} is set.
    * 5) After some number of checksumOk() calls, we will go back to using HBase checksum.
    * We will have 2 handles; however we presume checksums fail so rarely that we don't care.
    */
   private volatile FSDataInputStream stream = null;
   private volatile FSDataInputStream streamNoFsChecksum = null;
   private final Object streamNoFsChecksumFirstCreateLock = new Object();

   // The configuration states that we should validate hbase checksums
   private boolean useHBaseChecksumConfigured;

   // Record the current state of this reader with respect to
   // validating checkums in HBase. This is originally set the same
   // value as useHBaseChecksumConfigured, but can change state as and when
   // we encounter checksum verification failures.
   private volatile boolean useHBaseChecksum;

   // In the case of a checksum failure, do these many succeeding
   // reads without hbase checksum verification.
   private AtomicInteger hbaseChecksumOffCount = new AtomicInteger(-1);

   private final static ReadStatistics readStatistics = new ReadStatistics();

   private static class ReadStatistics {
     long totalBytesRead;
     long totalLocalBytesRead;
     long totalShortCircuitBytesRead;
     long totalZeroCopyBytesRead;
   }

   private Boolean instanceOfCanUnbuffer = null;
   private CanUnbuffer unbuffer = null;

   public FSDataInputStreamWrapper(FileSystem fs, Path path) throws IOException {
     this(fs, path, false, -1L);
   }

   public FSDataInputStreamWrapper(FileSystem fs, Path path, boolean dropBehind, long readahead) throws IOException {
     this(fs, null, path, dropBehind, readahead);
   }

   public FSDataInputStreamWrapper(FileSystem fs, FileLink link,
                                   boolean dropBehind, long readahead) throws IOException {
     this(fs, link, null, dropBehind, readahead);
   }

   private FSDataInputStreamWrapper(FileSystem fs, FileLink link, Path path, boolean dropBehind,
       long readahead) throws IOException {
     assert (path == null) != (link == null);
     this.path = path;
     this.link = link;
     this.doCloseStreams = true;
     this.dropBehind = dropBehind;
     this.readahead = readahead;
     // If the fs is not an instance of HFileSystem, then create an instance of HFileSystem
     // that wraps over the specified fs. In this case, we will not be able to avoid
     // checksumming inside the filesystem.
     this.hfs = (fs instanceof HFileSystem) ? (HFileSystem) fs : new HFileSystem(fs);

     // Initially we are going to read the tail block. Open the reader w/FS checksum.
     this.useHBaseChecksumConfigured = this.useHBaseChecksum = false;
     this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
     setStreamOptions(stream);
   }

   private void setStreamOptions(FSDataInputStream in) {
     try {
       in.setDropBehind(dropBehind);
     } catch (Exception e) {
       // Skipped.
     }
     if (readahead >= 0) {
       try {
         in.setReadahead(readahead);
       } catch (Exception e) {
         // Skipped.
       }
     }
   }

   /**
    * Prepares the streams for block reader. NOT THREAD SAFE. Must be called once, after any
    * reads finish and before any other reads start (what happens in reality is we read the
    * tail, then call this based on what's in the tail, then read blocks).
    * @param forceNoHBaseChecksum Force not using HBase checksum.
    */
   public void prepareForBlockReader(boolean forceNoHBaseChecksum) throws IOException {
     if (hfs == null) return;
     assert this.stream != null && !this.useHBaseChecksumConfigured;
     boolean useHBaseChecksum =
         !forceNoHBaseChecksum && hfs.useHBaseChecksum() && (hfs.getNoChecksumFs() != hfs);

     if (useHBaseChecksum) {
       FileSystem fsNc = hfs.getNoChecksumFs();
       this.streamNoFsChecksum = (link != null) ? link.open(fsNc) : fsNc.open(path);
       setStreamOptions(streamNoFsChecksum);
       this.useHBaseChecksumConfigured = this.useHBaseChecksum = useHBaseChecksum;
       // Close the checksum stream; we will reopen it if we get an HBase checksum failure.
       this.stream.close();
       this.stream = null;
     }
   }

   /** For use in tests. */
   public FSDataInputStreamWrapper(FSDataInputStream fsdis) {
     this(fsdis, fsdis);
   }

   /** For use in tests. */
   public FSDataInputStreamWrapper(FSDataInputStream fsdis, FSDataInputStream noChecksum) {
     doCloseStreams = false;
     stream = fsdis;
     streamNoFsChecksum = noChecksum;
     path = null;
     link = null;
     hfs = null;
     useHBaseChecksumConfigured = useHBaseChecksum = false;
     dropBehind = false;
     readahead = 0;
   }

   /**
    * @return Whether we are presently using HBase checksum.
    */
   public boolean shouldUseHBaseChecksum() {
     return this.useHBaseChecksum;
   }

   /**
    * Get the stream to use. Thread-safe.
    * @param useHBaseChecksum must be the value that shouldUseHBaseChecksum has returned
    *  at some point in the past, otherwise the result is undefined.
    */
   public FSDataInputStream getStream(boolean useHBaseChecksum) {
     return useHBaseChecksum ? this.streamNoFsChecksum : this.stream;
   }

   /**
    * Read from non-checksum stream failed, fall back to FS checksum. Thread-safe.
    * @param offCount For how many checksumOk calls to turn off the HBase checksum.
    */
   public FSDataInputStream fallbackToFsChecksum(int offCount) throws IOException {
     // checksumOffCount is speculative, but let's try to reset it less.
     boolean partOfConvoy = false;
     if (this.stream == null) {
       synchronized (streamNoFsChecksumFirstCreateLock) {
         partOfConvoy = (this.stream != null);
         if (!partOfConvoy) {
           this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
         }
       }
     }
     if (!partOfConvoy) {
       this.useHBaseChecksum = false;
       this.hbaseChecksumOffCount.set(offCount);
     }
     return this.stream;
   }

   /** Report that checksum was ok, so we may ponder going back to HBase checksum. */
   public void checksumOk() {
     if (this.useHBaseChecksumConfigured && !this.useHBaseChecksum
         && (this.hbaseChecksumOffCount.getAndDecrement() < 0)) {
       // The stream we need is already open (because we were using HBase checksum in the past).
       assert this.streamNoFsChecksum != null;
       this.useHBaseChecksum = true;
     }
   }

   private void updateInputStreamStatistics(FSDataInputStream stream) {
     // If the underlying file system is HDFS, update read statistics upon close.
     if (stream instanceof HdfsDataInputStream) {
       /**
        * Because HDFS ReadStatistics is calculated per input stream, it is not
        * feasible to update the aggregated number in real time. Instead, the
        * metrics are updated when an input stream is closed.
        */
       HdfsDataInputStream hdfsDataInputStream = (HdfsDataInputStream)stream;
       synchronized (readStatistics) {
         readStatistics.totalBytesRead += hdfsDataInputStream.getReadStatistics().
           getTotalBytesRead();
         readStatistics.totalLocalBytesRead += hdfsDataInputStream.getReadStatistics().
           getTotalLocalBytesRead();
         readStatistics.totalShortCircuitBytesRead += hdfsDataInputStream.getReadStatistics().
           getTotalShortCircuitBytesRead();
         readStatistics.totalZeroCopyBytesRead += hdfsDataInputStream.getReadStatistics().
           getTotalZeroCopyBytesRead();
       }
     }
   }

   public static long getTotalBytesRead() {
     synchronized (readStatistics) {
       return readStatistics.totalBytesRead;
     }
   }

   public static long getLocalBytesRead() {
     synchronized (readStatistics) {
       return readStatistics.totalLocalBytesRead;
     }
   }

   public static long getShortCircuitBytesRead() {
     synchronized (readStatistics) {
       return readStatistics.totalShortCircuitBytesRead;
     }
   }

   public static long getZeroCopyBytesRead() {
     synchronized (readStatistics) {
       return readStatistics.totalZeroCopyBytesRead;
     }
   }

   /** CloseClose stream(s) if necessary. */
   @Override
   public void close() {
     if (!doCloseStreams) {
       return;
     }
     updateInputStreamStatistics(this.streamNoFsChecksum);
     // we do not care about the close exception as it is for reading, no data loss issue.
     IOUtils.closeQuietly(streamNoFsChecksum);


     updateInputStreamStatistics(stream);
     IOUtils.closeQuietly(stream);
   }

   public HFileSystem getHfs() {
     return this.hfs;
   }

   /**
    * This will free sockets and file descriptors held by the stream only when the stream implements
    * org.apache.hadoop.fs.CanUnbuffer. NOT THREAD SAFE. Must be called only when all the clients
    * using this stream to read the blocks have finished reading. If by chance the stream is
    * unbuffered and there are clients still holding this stream for read then on next client read
    * request a new socket will be opened by Datanode without client knowing about it and will serve
    * its read request. Note: If this socket is idle for some time then the DataNode will close the
    * socket and the socket will move into CLOSE_WAIT state and on the next client request on this
    * stream, the current socket will be closed and a new socket will be opened to serve the
    * requests.
    */
   @SuppressWarnings({ "rawtypes" })
   public void unbuffer() {
     FSDataInputStream stream = this.getStream(this.shouldUseHBaseChecksum());
     if (stream != null) {
       InputStream wrappedStream = stream.getWrappedStream();
       // CanUnbuffer interface was added as part of HDFS-7694 and the fix is available in Hadoop
       // 2.6.4+ and 2.7.1+ versions only so check whether the stream object implements the
       // CanUnbuffer interface or not and based on that call the unbuffer api.
       final Class<? extends InputStream> streamClass = wrappedStream.getClass();
       if (this.instanceOfCanUnbuffer == null) {
         // To ensure we compute whether the stream is instance of CanUnbuffer only once.
         this.instanceOfCanUnbuffer = false;
         if (wrappedStream instanceof CanUnbuffer) {
           this.unbuffer = (CanUnbuffer) wrappedStream;
           this.instanceOfCanUnbuffer = true;
         }
       }
       if (this.instanceOfCanUnbuffer) {
         try {
           this.unbuffer.unbuffer();
         } catch (UnsupportedOperationException e){
           if (isLogTraceEnabled) {
             LOG.trace("Failed to invoke 'unbuffer' method in class " + streamClass
                 + " . So there may be the stream does not support unbuffering.", e);
           }
         }
       } else {
         if (isLogTraceEnabled) {
           LOG.trace("Failed to find 'unbuffer' method in class " + streamClass);
         }
       }
     }
   }
 }
	/**
	* 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.hadoop.hbase.io;

	import java.io.Closeable;
	import java.io.IOException;
	import java.io.InputStream;
	import java.util.concurrent.atomic.AtomicInteger;

	import org.apache.commons.io.IOUtils;
	import org.apache.hadoop.fs.CanUnbuffer;
	import org.apache.hadoop.fs.FSDataInputStream;
	import org.apache.hadoop.fs.FileSystem;
	import org.apache.hadoop.fs.Path;
	import org.apache.hadoop.hbase.fs.HFileSystem;
	import org.apache.hadoop.hdfs.client.HdfsDataInputStream;
	import org.apache.yetus.audience.InterfaceAudience;
	import org.slf4j.Logger;
	import org.slf4j.LoggerFactory;

	/**
	* Wrapper for input stream(s) that takes care of the interaction of FS and HBase checksums,
	* as well as closing streams. Initialization is not thread-safe, but normal operation is;
	* see method comments.
	*/
	@InterfaceAudience.Private
	public class FSDataInputStreamWrapper implements Closeable {
	private static final Logger LOG = LoggerFactory.getLogger(FSDataInputStreamWrapper.class);
	private static final boolean isLogTraceEnabled = LOG.isTraceEnabled();

	private final HFileSystem hfs;
	private final Path path;
	private final FileLink link;
	private final boolean doCloseStreams;
	private final boolean dropBehind;
	private final long readahead;

	/** Two stream handles, one with and one without FS-level checksum.
	* HDFS checksum setting is on FS level, not single read level, so you have to keep two
	* FS objects and two handles open to interleave different reads freely, which is very sad.
	* This is what we do:
	* 1) First, we need to read the trailer of HFile to determine checksum parameters.
	* We always use FS checksum to do that, so ctor opens {@link #stream}.
	* 2.1) After that, if HBase checksum is not used, we'd just always use {@link #stream};
	* 2.2) If HBase checksum can be used, we'll open {@link #streamNoFsChecksum},
	* and close {@link #stream}. User MUST call prepareForBlockReader for that to happen;
	* if they don't, (2.1) will be the default.
	* 3) The users can call {@link #shouldUseHBaseChecksum()}, and pass its result to
	* {@link #getStream(boolean)} to get stream (if Java had out/pointer params we could
	* return both in one call). This stream is guaranteed to be set.
	* 4) The first time HBase checksum fails, one would call {@link #fallbackToFsChecksum(int)}.
	* That will take lock, and open {@link #stream}. While this is going on, others will
	* continue to use the old stream; if they also want to fall back, they'll also call
	* {@link #fallbackToFsChecksum(int)}, and block until {@link #stream} is set.
	* 5) After some number of checksumOk() calls, we will go back to using HBase checksum.
	* We will have 2 handles; however we presume checksums fail so rarely that we don't care.
	*/
	private volatile FSDataInputStream stream = null;
	private volatile FSDataInputStream streamNoFsChecksum = null;
	private final Object streamNoFsChecksumFirstCreateLock = new Object();

	// The configuration states that we should validate hbase checksums
	private boolean useHBaseChecksumConfigured;

	// Record the current state of this reader with respect to
	// validating checkums in HBase. This is originally set the same
	// value as useHBaseChecksumConfigured, but can change state as and when
	// we encounter checksum verification failures.
	private volatile boolean useHBaseChecksum;

	// In the case of a checksum failure, do these many succeeding
	// reads without hbase checksum verification.
	private AtomicInteger hbaseChecksumOffCount = new AtomicInteger(-1);

	private final static ReadStatistics readStatistics = new ReadStatistics();

	private static class ReadStatistics {
	long totalBytesRead;
	long totalLocalBytesRead;
	long totalShortCircuitBytesRead;
	long totalZeroCopyBytesRead;
	}

	private Boolean instanceOfCanUnbuffer = null;
	private CanUnbuffer unbuffer = null;

	public FSDataInputStreamWrapper(FileSystem fs, Path path) throws IOException {
	this(fs, path, false, -1L);
	}

	public FSDataInputStreamWrapper(FileSystem fs, Path path, boolean dropBehind, long readahead) throws IOException {
	this(fs, null, path, dropBehind, readahead);
	}

	public FSDataInputStreamWrapper(FileSystem fs, FileLink link,
	boolean dropBehind, long readahead) throws IOException {
	this(fs, link, null, dropBehind, readahead);
	}

	private FSDataInputStreamWrapper(FileSystem fs, FileLink link, Path path, boolean dropBehind,
	long readahead) throws IOException {
	assert (path == null) != (link == null);
	this.path = path;
	this.link = link;
	this.doCloseStreams = true;
	this.dropBehind = dropBehind;
	this.readahead = readahead;
	// If the fs is not an instance of HFileSystem, then create an instance of HFileSystem
	// that wraps over the specified fs. In this case, we will not be able to avoid
	// checksumming inside the filesystem.
	this.hfs = (fs instanceof HFileSystem) ? (HFileSystem) fs : new HFileSystem(fs);

	// Initially we are going to read the tail block. Open the reader w/FS checksum.
	this.useHBaseChecksumConfigured = this.useHBaseChecksum = false;
	this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
	setStreamOptions(stream);
	}

	private void setStreamOptions(FSDataInputStream in) {
	try {
	in.setDropBehind(dropBehind);
	} catch (Exception e) {
	// Skipped.
	}
	if (readahead >= 0) {
	try {
	in.setReadahead(readahead);
	} catch (Exception e) {
	// Skipped.
	}
	}
	}

	/**
	* Prepares the streams for block reader. NOT THREAD SAFE. Must be called once, after any
	* reads finish and before any other reads start (what happens in reality is we read the
	* tail, then call this based on what's in the tail, then read blocks).
	* @param forceNoHBaseChecksum Force not using HBase checksum.
	*/
	public void prepareForBlockReader(boolean forceNoHBaseChecksum) throws IOException {
	if (hfs == null) return;
	assert this.stream != null && !this.useHBaseChecksumConfigured;
	boolean useHBaseChecksum =
	!forceNoHBaseChecksum && hfs.useHBaseChecksum() && (hfs.getNoChecksumFs() != hfs);

	if (useHBaseChecksum) {
	FileSystem fsNc = hfs.getNoChecksumFs();
	this.streamNoFsChecksum = (link != null) ? link.open(fsNc) : fsNc.open(path);
	setStreamOptions(streamNoFsChecksum);
	this.useHBaseChecksumConfigured = this.useHBaseChecksum = useHBaseChecksum;
	// Close the checksum stream; we will reopen it if we get an HBase checksum failure.
	this.stream.close();
	this.stream = null;
	}
	}

	/** For use in tests. */
	public FSDataInputStreamWrapper(FSDataInputStream fsdis) {
	this(fsdis, fsdis);
	}

	/** For use in tests. */
	public FSDataInputStreamWrapper(FSDataInputStream fsdis, FSDataInputStream noChecksum) {
	doCloseStreams = false;
	stream = fsdis;
	streamNoFsChecksum = noChecksum;
	path = null;
	link = null;
	hfs = null;
	useHBaseChecksumConfigured = useHBaseChecksum = false;
	dropBehind = false;
	readahead = 0;
	}

	/**
	* @return Whether we are presently using HBase checksum.
	*/
	public boolean shouldUseHBaseChecksum() {
	return this.useHBaseChecksum;
	}

	/**
	* Get the stream to use. Thread-safe.
	* @param useHBaseChecksum must be the value that shouldUseHBaseChecksum has returned
	* at some point in the past, otherwise the result is undefined.
	*/
	public FSDataInputStream getStream(boolean useHBaseChecksum) {
	return useHBaseChecksum ? this.streamNoFsChecksum : this.stream;
	}

	/**
	* Read from non-checksum stream failed, fall back to FS checksum. Thread-safe.
	* @param offCount For how many checksumOk calls to turn off the HBase checksum.
	*/
	public FSDataInputStream fallbackToFsChecksum(int offCount) throws IOException {
	// checksumOffCount is speculative, but let's try to reset it less.
	boolean partOfConvoy = false;
	if (this.stream == null) {
	synchronized (streamNoFsChecksumFirstCreateLock) {
	partOfConvoy = (this.stream != null);
	if (!partOfConvoy) {
	this.stream = (link != null) ? link.open(hfs) : hfs.open(path);
	}
	}
	}
	if (!partOfConvoy) {
	this.useHBaseChecksum = false;
	this.hbaseChecksumOffCount.set(offCount);
	}
	return this.stream;
	}

	/** Report that checksum was ok, so we may ponder going back to HBase checksum. */
	public void checksumOk() {
	if (this.useHBaseChecksumConfigured && !this.useHBaseChecksum
	&& (this.hbaseChecksumOffCount.getAndDecrement() < 0)) {
	// The stream we need is already open (because we were using HBase checksum in the past).
	assert this.streamNoFsChecksum != null;
	this.useHBaseChecksum = true;
	}
	}

	private void updateInputStreamStatistics(FSDataInputStream stream) {
	// If the underlying file system is HDFS, update read statistics upon close.
	if (stream instanceof HdfsDataInputStream) {
	/**
	* Because HDFS ReadStatistics is calculated per input stream, it is not
	* feasible to update the aggregated number in real time. Instead, the
	* metrics are updated when an input stream is closed.
	*/
	HdfsDataInputStream hdfsDataInputStream = (HdfsDataInputStream)stream;
	synchronized (readStatistics) {
	readStatistics.totalBytesRead += hdfsDataInputStream.getReadStatistics().
	getTotalBytesRead();
	readStatistics.totalLocalBytesRead += hdfsDataInputStream.getReadStatistics().
	getTotalLocalBytesRead();
	readStatistics.totalShortCircuitBytesRead += hdfsDataInputStream.getReadStatistics().
	getTotalShortCircuitBytesRead();
	readStatistics.totalZeroCopyBytesRead += hdfsDataInputStream.getReadStatistics().
	getTotalZeroCopyBytesRead();
	}
	}
	}

	public static long getTotalBytesRead() {
	synchronized (readStatistics) {
	return readStatistics.totalBytesRead;
	}
	}

	public static long getLocalBytesRead() {
	synchronized (readStatistics) {
	return readStatistics.totalLocalBytesRead;
	}
	}

	public static long getShortCircuitBytesRead() {
	synchronized (readStatistics) {
	return readStatistics.totalShortCircuitBytesRead;
	}
	}

	public static long getZeroCopyBytesRead() {
	synchronized (readStatistics) {
	return readStatistics.totalZeroCopyBytesRead;
	}
	}

	/** CloseClose stream(s) if necessary. */
	@Override
	public void close() {
	if (!doCloseStreams) {
	return;
	}
	updateInputStreamStatistics(this.streamNoFsChecksum);
	// we do not care about the close exception as it is for reading, no data loss issue.
	IOUtils.closeQuietly(streamNoFsChecksum);


	updateInputStreamStatistics(stream);
	IOUtils.closeQuietly(stream);
	}

	public HFileSystem getHfs() {
	return this.hfs;
	}

	/**
	* This will free sockets and file descriptors held by the stream only when the stream implements
	* org.apache.hadoop.fs.CanUnbuffer. NOT THREAD SAFE. Must be called only when all the clients
	* using this stream to read the blocks have finished reading. If by chance the stream is
	* unbuffered and there are clients still holding this stream for read then on next client read
	* request a new socket will be opened by Datanode without client knowing about it and will serve
	* its read request. Note: If this socket is idle for some time then the DataNode will close the
	* socket and the socket will move into CLOSE_WAIT state and on the next client request on this
	* stream, the current socket will be closed and a new socket will be opened to serve the
	* requests.
	*/
	@SuppressWarnings({ "rawtypes" })
	public void unbuffer() {
	FSDataInputStream stream = this.getStream(this.shouldUseHBaseChecksum());
	if (stream != null) {
	InputStream wrappedStream = stream.getWrappedStream();
	// CanUnbuffer interface was added as part of HDFS-7694 and the fix is available in Hadoop
	// 2.6.4+ and 2.7.1+ versions only so check whether the stream object implements the
	// CanUnbuffer interface or not and based on that call the unbuffer api.
	final Class<? extends InputStream> streamClass = wrappedStream.getClass();
	if (this.instanceOfCanUnbuffer == null) {
	// To ensure we compute whether the stream is instance of CanUnbuffer only once.
	this.instanceOfCanUnbuffer = false;
	if (wrappedStream instanceof CanUnbuffer) {
	this.unbuffer = (CanUnbuffer) wrappedStream;
	this.instanceOfCanUnbuffer = true;
	}
	}
	if (this.instanceOfCanUnbuffer) {
	try {
	this.unbuffer.unbuffer();
	} catch (UnsupportedOperationException e){
	if (isLogTraceEnabled) {
	LOG.trace("Failed to invoke 'unbuffer' method in class " + streamClass
	+ " . So there may be the stream does not support unbuffering.", e);
	}
	}
	} else {
	if (isLogTraceEnabled) {
	LOG.trace("Failed to find 'unbuffer' method in class " + streamClass);
	}
	}
	}
	}
	}