/**
 * 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.regionserver.snapshot;

import java.util.List;
import java.util.concurrent.Callable;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.hbase.errorhandling.ForeignException;
import org.apache.hadoop.hbase.errorhandling.ForeignExceptionDispatcher;
import org.apache.hadoop.hbase.procedure.ProcedureMember;
import org.apache.hadoop.hbase.procedure.Subprocedure;
import org.apache.hadoop.hbase.protobuf.generated.HBaseProtos.SnapshotDescription;
import org.apache.hadoop.hbase.regionserver.HRegion;
import org.apache.hadoop.hbase.regionserver.snapshot.RegionServerSnapshotManager.SnapshotSubprocedurePool;
import org.apache.hadoop.hbase.snapshot.SnapshotDescriptionUtils;

/**
 * This online snapshot implementation uses the distributed procedure framework to force a
 * store flush and then records the hfiles.  Its enter stage does nothing.  Its leave stage then
 * flushes the memstore, builds the region server's snapshot manifest from its hfiles list, and
 * copies .regioninfos into the snapshot working directory.  At the master side, there is an atomic
 * rename of the working dir into the proper snapshot directory.
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class FlushSnapshotSubprocedure extends Subprocedure {
  private static final Log LOG = LogFactory.getLog(FlushSnapshotSubprocedure.class);

  private final List<HRegion> regions;
  private final SnapshotDescription snapshot;
  private final SnapshotSubprocedurePool taskManager;

  public FlushSnapshotSubprocedure(ProcedureMember member,
      ForeignExceptionDispatcher errorListener, long wakeFrequency, long timeout,
      List<HRegion> regions, SnapshotDescription snapshot,
      SnapshotSubprocedurePool taskManager) {
    super(member, snapshot.getName(), errorListener, wakeFrequency, timeout);
    this.snapshot = snapshot;
    this.regions = regions;
    this.taskManager = taskManager;
  }

  /**
   * Callable for adding files to snapshot manifest working dir.  Ready for multithreading.
   */
  private class RegionSnapshotTask implements Callable<Void> {
    HRegion region;
    RegionSnapshotTask(HRegion region) {
      this.region = region;
    }

    @Override
    public Void call() throws Exception {
      // Taking the region read lock prevents the individual region from being closed while a
      // snapshot is in progress.  This is helpful but not sufficient for preventing races with
      // snapshots that involve multiple regions and regionservers.  It is still possible to have
      // an interleaving such that globally regions are missing, so we still need the verification
      // step.
      LOG.debug("Starting region operation on " + region);
      region.startRegionOperation();
      try {
        LOG.debug("Flush Snapshotting region " + region.toString() + " started...");
        region.flushcache();
        region.addRegionToSnapshot(snapshot, monitor);
        LOG.debug("... Flush Snapshotting region " + region.toString() + " completed.");
      } finally {
        LOG.debug("Closing region operation on " + region);
        region.closeRegionOperation();
      }
      return null;
    }
  }

  private void flushSnapshot() throws ForeignException {
    if (regions.isEmpty()) {
      // No regions on this RS, we are basically done.
      return;
    }

    monitor.rethrowException();

    // assert that the taskManager is empty.
    if (taskManager.hasTasks()) {
      throw new IllegalStateException("Attempting to take snapshot "
          + SnapshotDescriptionUtils.toString(snapshot)
          + " but we currently have outstanding tasks");
    }
    
    // Add all hfiles already existing in region.
    for (HRegion region : regions) {
      // submit one task per region for parallelize by region.
      taskManager.submitTask(new RegionSnapshotTask(region));
      monitor.rethrowException();
    }

    // wait for everything to complete.
    LOG.debug("Flush Snapshot Tasks submitted for " + regions.size() + " regions");
    try {
      taskManager.waitForOutstandingTasks();
    } catch (InterruptedException e) {
      throw new ForeignException(getMemberName(), e);
    }
  }

  /**
   * do nothing, core of snapshot is executed in {@link #insideBarrier} step.
   */
  @Override
  public void acquireBarrier() throws ForeignException {
    // NO OP
  }

  /**
   * do a flush snapshot of every region on this rs from the target table.
   */
  @Override
  public void insideBarrier() throws ForeignException {
    flushSnapshot();
  }

  /**
   * Cancel threads if they haven't finished.
   */
  @Override
  public void cleanup(Exception e) {
    LOG.info("Aborting all online FLUSH snapshot subprocedure task threads for '"
        + snapshot.getName() + "' due to error", e);
    try {
      taskManager.cancelTasks();
    } catch (InterruptedException e1) {
      Thread.currentThread().interrupt();
    }
  }

  /**
   * Hooray!
   */
  public void releaseBarrier() {
    // NO OP
  }

}