org.apache.hadoop.hdfs.server.namenode.bookkeeper.BookKeeperJournalOutputStream.java Source code

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Here is the source code for org.apache.hadoop.hdfs.server.namenode.bookkeeper.BookKeeperJournalOutputStream.java

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/**
 * 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.server.namenode.bookkeeper;

import org.apache.bookkeeper.client.BKException;
import org.apache.bookkeeper.client.LedgerHandle;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hdfs.server.namenode.EditsDoubleBuffer;

import java.io.IOException;
import java.io.OutputStream;

/**
 * Wrapper OutputStream for that {@link EditsDoubleBuffer} in
 * {@link BookKeeperEditLogOutputStream} will flush to. This is a
 * re-write of BookKeeper's own LedgerOutputStream which ensures that
 * any exception thrown (e.g., if we are unable to confirm that we've
 * written to a quorum of bookies) is propagated back to the caller.
 * <p>
 * A new entry is created whenever any of the write methods are called.
 * Note: it is the responsibility of the class that created the instance
 * to close the underlying ledger.
 *
 * @see org.apache.bookkeeper.streaming.LedgerOutputStream
 */
public class BookKeeperJournalOutputStream extends OutputStream {

    private static final Log LOG = LogFactory.getLog(BookKeeperJournalOutputStream.class);

    private final LedgerHandle ledger; // The underlying ledger

    /**
     * Creates an {@link OutputStream} wrapping a BookKeeper ledger
     * @param ledger The ledger that writes will go to. It is the caller's
     *               responsibility to close the ledger.
     */
    public BookKeeperJournalOutputStream(LedgerHandle ledger) {
        this.ledger = ledger;
    }

    /**
     * Write the buffer to a new entry in a BookKeeper ledger or throw
     * an IOException if we are unable to successfully write to a quorum
     * of bookies
     * @param buf Buffer to write from
     * @param off Offset in the buffer
     * @param len How many bytes to write, starting the offset
     * @throws IOException If we are interrupted while writing to BookKeeper or
     *                     if we are unable to successfully add the entry to
     *                     a quorum of bookies.
     */
    private synchronized void addBookKeeperEntry(byte[] buf, int off, int len) throws IOException {
        try {
            ledger.addEntry(buf, off, len);
            if (LOG.isDebugEnabled()) {
                LOG.debug("Last add pushed to ledger " + ledger.getId() + " is " + ledger.getLastAddPushed());
                LOG.debug("Last add confirmed to ledger " + ledger.getId() + " is " + ledger.getLastAddConfirmed());
            }
        } catch (InterruptedException e) {
            Thread.currentThread().interrupt();
            throw new IOException("Interrupted writing to BookKeeper", e);
        } catch (BKException e) {
            throw new IOException("Failed to write to BookKeeper", e);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void write(int i) throws IOException {
        byte oneByte[] = new byte[] { (byte) (i & 0xff) };
        addBookKeeperEntry(oneByte, 0, 1);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void write(byte[] buf) throws IOException {
        addBookKeeperEntry(buf, 0, buf.length);
    }

    /**
     * Write the buffer to a new entry in a BookKeeper ledger.
     * @see OutputStream#write(byte[], int, int)
     * @see #addBookKeeperEntry(byte[], int, int)
     * @throws IOException If there is an error adding the BookKeeper entry.
     */
    @Override
    public void write(byte[] buf, int off, int len) throws IOException {
        addBookKeeperEntry(buf, off, len);
    }
}