org.apache.hadoop.hdfs.client.ClientMmap.java Source code

Introduction

Here is the source code for org.apache.hadoop.hdfs.client.ClientMmap.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.hdfs.client;

import java.io.FileInputStream;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.hdfs.protocol.DatanodeID;
import org.apache.hadoop.hdfs.protocol.ExtendedBlock;
import org.apache.hadoop.io.nativeio.NativeIO;

import java.io.IOException;
import java.lang.ref.WeakReference;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel.MapMode;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.google.common.annotations.VisibleForTesting;

/**
 * A memory-mapped region used by an HDFS client.
 * 
 * This class includes a reference count and some other information used by
 * ClientMmapManager to track and cache mmaps.
 */
@InterfaceAudience.Private
public class ClientMmap {
    static final Log LOG = LogFactory.getLog(ClientMmap.class);

    /**
     * A reference to the manager of this mmap.
     * 
     * This is only a weak reference to help minimize the damange done by
     * code which leaks references accidentally.
     */
    private final WeakReference<ClientMmapManager> manager;

    /**
     * The actual mapped memory region.
     */
    private final MappedByteBuffer map;

    /**
     * A reference count tracking how many threads are using this object.
     */
    private final AtomicInteger refCount = new AtomicInteger(1);

    /**
     * Block pertaining to this mmap
     */
    private final ExtendedBlock block;

    /**
     * The DataNode where this mmap came from.
     */
    private final DatanodeID datanodeID;

    /**
     * The monotonic time when this mmap was last evictable.
     */
    private long lastEvictableTimeNs;

    public static ClientMmap load(ClientMmapManager manager, FileInputStream in, ExtendedBlock block,
            DatanodeID datanodeID) throws IOException {
        MappedByteBuffer map = in.getChannel().map(MapMode.READ_ONLY, 0, in.getChannel().size());
        return new ClientMmap(manager, map, block, datanodeID);
    }

    private ClientMmap(ClientMmapManager manager, MappedByteBuffer map, ExtendedBlock block, DatanodeID datanodeID)
            throws IOException {
        this.manager = new WeakReference<ClientMmapManager>(manager);
        this.map = map;
        this.block = block;
        this.datanodeID = datanodeID;
        this.lastEvictableTimeNs = 0;
    }

    /**
     * Decrement the reference count on this object.
     * Should be called with the ClientMmapManager lock held.
     */
    public void unref() {
        int count = refCount.decrementAndGet();
        if (count < 0) {
            throw new IllegalArgumentException(
                    "can't decrement the " + "reference count on this ClientMmap lower than 0.");
        } else if (count == 0) {
            ClientMmapManager man = manager.get();
            if (man == null) {
                unmap();
            } else {
                man.makeEvictable(this);
            }
        }
    }

    /**
     * Increment the reference count on this object.
     *
     * @return     The new reference count.
     */
    public int ref() {
        return refCount.getAndIncrement();
    }

    @VisibleForTesting
    public ExtendedBlock getBlock() {
        return block;
    }

    DatanodeID getDatanodeID() {
        return datanodeID;
    }

    public MappedByteBuffer getMappedByteBuffer() {
        return map;
    }

    public void setLastEvictableTimeNs(long lastEvictableTimeNs) {
        this.lastEvictableTimeNs = lastEvictableTimeNs;
    }

    public long getLastEvictableTimeNs() {
        return this.lastEvictableTimeNs;
    }

    /**
     * Unmap the memory region.
     */
    void unmap() {
        assert (refCount.get() == 0);
        NativeIO.POSIX.munmap(map);
    }
}