branch-2.0.4-alpha/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/SafeMode.java

/**
 * 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;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.hdfs.protocol.Block;

/** SafeMode related operations. */
@InterfaceAudience.Private
public interface SafeMode {
  /**
   * Check safe mode conditions.
   * If the corresponding conditions are satisfied,
   * trigger the system to enter/leave safe mode.
   */
  public void checkSafeMode();

  /** Is the system in safe mode? */
  public boolean isInSafeMode();

  /**
   * Is the system in startup safe mode, i.e. the system is starting up with
   * safe mode turned on automatically?
   */
  public boolean isInStartupSafeMode();

  /** Check whether replication queues are being populated. */
  public boolean isPopulatingReplQueues();
    
  /**
   * Increment number of blocks that reached minimal replication.
   * @param replication current replication 
   */
  public void incrementSafeBlockCount(int replication);

  /** Decrement number of blocks that reached minimal replication. */
  public void decrementSafeBlockCount(Block b);
}