org.apache.hadoop.hbase.io.FSDataInputStreamWrapper.java Source code

Java tutorial

Introduction

Here is the source code for org.apache.hadoop.hbase.io.FSDataInputStreamWrapper.java

Source

/**
 * 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.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.commons.io.IOUtils;
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.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;

/**
 * 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 Boolean instanceOfCanUnbuffer = null;
    // Using reflection to get org.apache.hadoop.fs.CanUnbuffer#unbuffer method to avoid compilation
    // errors against Hadoop pre 2.6.4 and 2.7.1 versions.
    private Method 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. */
    @VisibleForTesting
    public FSDataInputStreamWrapper(FSDataInputStream fsdis) {
        this(fsdis, fsdis);
    }

    /** For use in tests. */
    @VisibleForTesting
    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;
        }
    }

    /** Close stream(s) if necessary. */
    @Override
    public void close() {
        if (!doCloseStreams) {
            return;
        }
        // we do not care about the close exception as it is for reading, no data loss issue.
        IOUtils.closeQuietly(streamNoFsChecksum);
        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;
                Class<?>[] streamInterfaces = streamClass.getInterfaces();
                for (Class c : streamInterfaces) {
                    if (c.getCanonicalName().toString().equals("org.apache.hadoop.fs.CanUnbuffer")) {
                        try {
                            this.unbuffer = streamClass.getDeclaredMethod("unbuffer");
                        } catch (NoSuchMethodException | SecurityException e) {
                            if (isLogTraceEnabled) {
                                LOG.trace("Failed to find 'unbuffer' method in class " + streamClass
                                        + " . So there may be a TCP socket connection "
                                        + "left open in CLOSE_WAIT state.", e);
                            }
                            return;
                        }
                        this.instanceOfCanUnbuffer = true;
                        break;
                    }
                }
            }
            if (this.instanceOfCanUnbuffer) {
                try {
                    this.unbuffer.invoke(wrappedStream);
                } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
                    if (isLogTraceEnabled) {
                        LOG.trace("Failed to invoke 'unbuffer' method in class " + streamClass
                                + " . So there may be a TCP socket connection left open in CLOSE_WAIT state.", e);
                    }
                }
            } else {
                if (isLogTraceEnabled) {
                    LOG.trace("Failed to find 'unbuffer' method in class " + streamClass
                            + " . So there may be a TCP socket connection "
                            + "left open in CLOSE_WAIT state. For more details check "
                            + "https://issues.apache.org/jira/browse/HBASE-9393");
                }
            }
        }
    }
}