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Main functionality for HBase
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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.hbase.wal;

import java.io.IOException;
import java.util.List;
import java.util.Set;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicLong;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
// imports for things that haven't moved from regionserver.wal yet.
import org.apache.hadoop.hbase.regionserver.wal.WALActionsListener;
import org.apache.hadoop.hbase.regionserver.wal.WALCoprocessorHost;
import org.apache.hadoop.hbase.regionserver.wal.WALEdit;
import org.apache.hadoop.hbase.util.FSUtils;

/**
 * No-op implementation of {@link WALProvider} used when the WAL is disabled.
 *
 * Should only be used when severe data loss is acceptable.
 *
 */
@InterfaceAudience.Private
class DisabledWALProvider implements WALProvider {

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

  WAL disabled;

  @Override
  public void init(final WALFactory factory, final Configuration conf,
      final List listeners, String providerId) throws IOException {
    if (null != disabled) {
      throw new IllegalStateException("WALProvider.init should only be called once.");
    }
    if (null == providerId) {
      providerId = "defaultDisabled";
    }
    disabled = new DisabledWAL(new Path(FSUtils.getRootDir(conf), providerId), conf, null);
  }

  @Override
  public WAL getWAL(final byte[] identifier) throws IOException {
    return disabled;
  }

  @Override
  public void close() throws IOException {
    disabled.close();
  }

  @Override
  public void shutdown() throws IOException {
    disabled.shutdown();
  }

  private static class DisabledWAL implements WAL {
    protected final List listeners =
        new CopyOnWriteArrayList();
    protected final Path path;
    protected final WALCoprocessorHost coprocessorHost;
    protected final AtomicBoolean closed = new AtomicBoolean(false);

    public DisabledWAL(final Path path, final Configuration conf,
        final List listeners) {
      this.coprocessorHost = new WALCoprocessorHost(this, conf);
      this.path = path;
      if (null != listeners) {
        for(WALActionsListener listener : listeners) {
          registerWALActionsListener(listener);
        }
      }
    }

    @Override
    public void registerWALActionsListener(final WALActionsListener listener) {
      listeners.add(listener);
    }
    
    @Override
    public boolean unregisterWALActionsListener(final WALActionsListener listener) {
      return listeners.remove(listener);
    }

    @Override
    public byte[][] rollWriter() {
      if (!listeners.isEmpty()) {
        for (WALActionsListener listener : listeners) {
          listener.logRollRequested(false);
        }
        for (WALActionsListener listener : listeners) {
          try {
            listener.preLogRoll(path, path);
          } catch (IOException exception) {
            LOG.debug("Ignoring exception from listener.", exception);
          }
        }
        for (WALActionsListener listener : listeners) {
          try {
            listener.postLogRoll(path, path);
          } catch (IOException exception) {
            LOG.debug("Ignoring exception from listener.", exception);
          }
        }
      }
      return null;
    }

    @Override
    public byte[][] rollWriter(boolean force) {
      return rollWriter();
    }

    @Override
    public void shutdown() {
      if(closed.compareAndSet(false, true)) {
        if (!this.listeners.isEmpty()) {
          for (WALActionsListener listener : this.listeners) {
            listener.logCloseRequested();
          }
        }
      }
    }

    @Override
    public void close() {
      shutdown();
    }

    @Override
    public long append(HTableDescriptor htd, HRegionInfo info, WALKey key, WALEdit edits,
        AtomicLong sequenceId, boolean inMemstore, List memstoreKVs) {
      if (!this.listeners.isEmpty()) {
        final long start = System.nanoTime();
        long len = 0;
        for (Cell cell : edits.getCells()) {
          len += CellUtil.estimatedSerializedSizeOf(cell);
        }
        final long elapsed = (System.nanoTime() - start)/1000000l;
        for (WALActionsListener listener : this.listeners) {
          listener.postAppend(len, elapsed);
        }
      }
      return -1;
    }

    @Override
    public void sync() {
      if (!this.listeners.isEmpty()) {
        for (WALActionsListener listener : this.listeners) {
          listener.postSync(0l, 0);
        }
      }
    }

    @Override
    public void sync(long txid) {
      sync();
    }

    @Override
    public Long startCacheFlush(final byte[] encodedRegionName, Set flushedFamilyNames) {
      if (closed.get()) return null;
      return HConstants.NO_SEQNUM;
    }

    @Override
    public void completeCacheFlush(final byte[] encodedRegionName) {
    }

    @Override
    public void abortCacheFlush(byte[] encodedRegionName) {
    }

    @Override
    public WALCoprocessorHost getCoprocessorHost() {
      return coprocessorHost;
    }

    @Override
    public long getEarliestMemstoreSeqNum(byte[] encodedRegionName) {
      return HConstants.NO_SEQNUM;
    }

    @Override
    public long getEarliestMemstoreSeqNum(byte[] encodedRegionName, byte[] familyName) {
      return HConstants.NO_SEQNUM;
    }

    @Override
    public String toString() {
      return "WAL disabled.";
    }
  }
}