/**
    *
    * 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;
  
  import java.text.SimpleDateFormat;
  import java.util.Date;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.conf.Configuration;
  import org.apache.hadoop.hbase.HConstants;
  import org.apache.hadoop.hbase.ScheduledChore;
  import org.apache.hadoop.hbase.Stoppable;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
  import org.apache.hadoop.hbase.util.NonceKey;
  
  import com.google.common.annotations.VisibleForTesting;
  
  /**
   * Implementation of nonce manager that stores nonces in a hash map and cleans them up after
   * some time; if nonce group/client ID is supplied, nonces are stored by client ID.
   */
  @InterfaceAudience.Private
  public class ServerNonceManager {
    public static final String HASH_NONCE_GRACE_PERIOD_KEY = "hbase.server.hashNonce.gracePeriod";
    private static final Log LOG = LogFactory.getLog(ServerNonceManager.class);
  
    /** The time to wait in an extremely unlikely case of a conflict with a running op.
     * Only here so that tests could override it and not wait. */
    private int conflictWaitIterationMs = 30000;
  
    private static final SimpleDateFormat tsFormat = new SimpleDateFormat("HH:mm:ss.SSS");
  
    // This object is used to synchronize on in case of collisions, and for cleanup.
    private static class OperationContext {
      static final int DONT_PROCEED = 0;
      static final int PROCEED = 1;
      static final int WAIT = 2;
  
      // 0..1 - state, 2..2 - whether anyone is waiting, 3.. - ts of last activity
      private long data = 0;
      private static final long STATE_BITS = 3;
      private static final long WAITING_BIT = 4;
      private static final long ALL_FLAG_BITS = WAITING_BIT | STATE_BITS;
  
      @Override
      public String toString() {
        return "[state " + getState() + ", hasWait " + hasWait() + ", activity "
            + tsFormat.format(new Date(getActivityTime())) + "]";
      }
  
      public OperationContext() {
        setState(WAIT);
        reportActivity();
      }
  
      public void setState(int state) {
        this.data = (this.data & ~STATE_BITS) | state;
      }
  
      public int getState() {
        return (int)(this.data & STATE_BITS);
      }
  
      public void setHasWait() {
        this.data = this.data | WAITING_BIT;
      }
  
      public boolean hasWait() {
        return (this.data & WAITING_BIT) == WAITING_BIT;
      }
  
      public void reportActivity() {
        long now = EnvironmentEdgeManager.currentTime();
        this.data = (this.data & ALL_FLAG_BITS) | (now << 3);
      }
  
      public boolean isExpired(long minRelevantTime) {
        return getActivityTime() < (minRelevantTime & (~0l >>> 3));
      }
 
     private long getActivityTime() {
       return this.data >>> 3;
     }
   }
 
   /**
    * Nonces.
    * Approximate overhead per nonce: 64 bytes from hashmap, 32 from two objects (k/v),
    * NK: 16 bytes (2 longs), OC: 8 bytes (1 long) - so, 120 bytes.
    * With 30min expiration time, 5k increments/appends per sec., we'd use approximately 1Gb,
    * which is a realistic worst case. If it's much worse, we could use some sort of memory
    * limit and cleanup.
    */
   private ConcurrentHashMap<NonceKey, OperationContext> nonces =
       new ConcurrentHashMap<NonceKey, OperationContext>();
 
   private int deleteNonceGracePeriod;
 
   public ServerNonceManager(Configuration conf) {
     // Default - 30 minutes.
     deleteNonceGracePeriod = conf.getInt(HASH_NONCE_GRACE_PERIOD_KEY, 30 * 60 * 1000);
     if (deleteNonceGracePeriod < 60 * 1000) {
       LOG.warn("Nonce grace period " + deleteNonceGracePeriod
           + " is less than a minute; might be too small to be useful");
     }
   }
 
   @VisibleForTesting
   public void setConflictWaitIterationMs(int conflictWaitIterationMs) {
     this.conflictWaitIterationMs = conflictWaitIterationMs;
   }
 
   /**
    * Starts the operation if operation with such nonce has not already succeeded. If the
    * operation is in progress, waits for it to end and checks whether it has succeeded.
    * @param group Nonce group.
    * @param nonce Nonce.
    * @param stoppable Stoppable that terminates waiting (if any) when the server is stopped.
    * @return true if the operation has not already succeeded and can proceed; false otherwise.
    */
   public boolean startOperation(long group, long nonce, Stoppable stoppable)
       throws InterruptedException {
     if (nonce == HConstants.NO_NONCE) return true;
     NonceKey nk = new NonceKey(group, nonce);
     OperationContext ctx = new OperationContext();
     while (true) {
       OperationContext oldResult = nonces.putIfAbsent(nk, ctx);
       if (oldResult == null) return true;
 
       // Collision with some operation - should be extremely rare.
       synchronized (oldResult) {
         int oldState = oldResult.getState();
         LOG.debug("Conflict detected by nonce: " + nk + ", " + oldResult);
         if (oldState != OperationContext.WAIT) {
           return oldState == OperationContext.PROCEED; // operation ended
         }
         oldResult.setHasWait();
         oldResult.wait(this.conflictWaitIterationMs); // operation is still active... wait and loop
         if (stoppable.isStopped()) {
           throw new InterruptedException("Server stopped");
         }
       }
     }
   }
 
   /**
    * Ends the operation started by startOperation.
    * @param group Nonce group.
    * @param nonce Nonce.
    * @param success Whether the operation has succeeded.
    */
   public void endOperation(long group, long nonce, boolean success) {
     if (nonce == HConstants.NO_NONCE) return;
     NonceKey nk = new NonceKey(group, nonce);
     OperationContext newResult = nonces.get(nk);
     assert newResult != null;
     synchronized (newResult) {
       assert newResult.getState() == OperationContext.WAIT;
       // If we failed, other retries can proceed.
       newResult.setState(success ? OperationContext.DONT_PROCEED : OperationContext.PROCEED);
       if (success) {
         newResult.reportActivity(); // Set time to use for cleanup.
       } else {
         OperationContext val = nonces.remove(nk);
         assert val == newResult;
       }
       if (newResult.hasWait()) {
         LOG.debug("Conflict with running op ended: " + nk + ", " + newResult);
         newResult.notifyAll();
       }
     }
   }
 
   /**
    * Reports the operation from WAL during replay.
    * @param group Nonce group.
    * @param nonce Nonce.
    * @param writeTime Entry write time, used to ignore entries that are too old.
    */
   public void reportOperationFromWal(long group, long nonce, long writeTime) {
     if (nonce == HConstants.NO_NONCE) return;
     // Give the write time some slack in case the clocks are not synchronized.
     long now = EnvironmentEdgeManager.currentTime();
     if (now > writeTime + (deleteNonceGracePeriod * 1.5)) return;
     OperationContext newResult = new OperationContext();
     newResult.setState(OperationContext.DONT_PROCEED);
     NonceKey nk = new NonceKey(group, nonce);
     OperationContext oldResult = nonces.putIfAbsent(nk, newResult);
     if (oldResult != null) {
       // Some schemes can have collisions (for example, expiring hashes), so just log it.
       // We have no idea about the semantics here, so this is the least of many evils.
       LOG.warn("Nonce collision during WAL recovery: " + nk
           + ", " + oldResult + " with " + newResult);
     }
   }
 
   /**
    * Creates a scheduled chore that is used to clean up old nonces.
    * @param stoppable Stoppable for the chore.
    * @return ScheduledChore; the scheduled chore is not started.
    */
   public ScheduledChore createCleanupScheduledChore(Stoppable stoppable) {
     // By default, it will run every 6 minutes (30 / 5).
     return new ScheduledChore("nonceCleaner", stoppable, deleteNonceGracePeriod / 5) {
       @Override
       protected void chore() {
         cleanUpOldNonces();
       }
     };
   }
 
   private void cleanUpOldNonces() {
     long cutoff = EnvironmentEdgeManager.currentTime() - deleteNonceGracePeriod;
     for (Map.Entry<NonceKey, OperationContext> entry : nonces.entrySet()) {
       OperationContext oc = entry.getValue();
       if (!oc.isExpired(cutoff)) continue;
       synchronized (oc) {
         if (oc.getState() == OperationContext.WAIT || !oc.isExpired(cutoff)) continue;
         nonces.remove(entry.getKey());
       }
     }
   }
 }