code: /**
  Copyright (c) 2007-2013 Alysson Bessani, Eduardo Alchieri, Paulo Sousa, and the authors indicated in the @author tags
  
  Licensed 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 bftsmart.consensus;
  
  import java.util.Arrays;
  import java.util.HashMap;
  import java.util.HashSet;
  import java.util.Set;
  import java.util.concurrent.locks.ReentrantLock;
  
  import bftsmart.tom.core.ExecutionManager;
  import bftsmart.reconfiguration.ServerViewController;
  import bftsmart.tom.util.Logger;
  
  
  
  /**
   * This class stands for a das instance that implements the algorithm
   * for the Byzantine fault model described in Cachin's 'Yet Another Visit to Paxos' (April 2011)
   */
  public class Consensus {
      private final static org.apache.log4j.Logger logger = org.apache.log4j.Logger.getLogger(Consensus.class);
      private ExecutionManager manager; // Execution manager for this replica's das instances
  
      private Decision decision; // Decision instance to which this das works for
      private HashMap<Integer,Epoch> epochs = new HashMap<Integer,Epoch>(2);
      private ReentrantLock epochsLock = new ReentrantLock(); // Lock for concurrency control
      private ReentrantLock writeSetLock = new ReentrantLock(); //lock for this das write set
  
      private boolean decided; // Is this das decided?
      private int decisionEpoch = -1; // epoch at which a decision was made
  
      //NEW ATTRIBUTES FOR THE LEADER CHANGE
      private int ets = 0;
      private TimestampValuePair quorumWrites = null;
      private HashSet<TimestampValuePair> writeSet = new HashSet<TimestampValuePair>();
  
      public ReentrantLock lock = new ReentrantLock(); //this das lock (called by other classes)
      
      /**
       * Creates a new instance of Consensus
       * 
       * Important: At this point, the 'decision' parameter is only a placeholder
       * for the future decision, and should not be delivered to the delivery thread.
       * 
       * Use 'isDecided()' to check if the das already decided a value.
       * 
       * @param manager Execution manager for this replica's das instances
       * @param decision Decision instance to which this das works for.
       */
      public Consensus(ExecutionManager manager, Decision decision) {
          this.manager = manager;
          this.decision = decision;
      }
  
      /**
       * This is the das ID
       * @return Consensus ID
       */
      public int getId() {
          return decision.getConsensusId();
      }
  
      /**
       * This is the execution manager for this replica's das instances
       * @return Execution manager for this replica
       */
      public ExecutionManager getManager() {
          return manager;
      }
  
      /**
       * This is the decision instance to which this das works for
       * 
       * Important: The returned object should only be sent to the delivery thread
       * after this das instance decides a value. Use 'isDecided()' to check if
       * the das already decided a value.
       * 
       * @return Decision instance to which this das works for
       */
      public Decision getDecision() {
          return decision;
      }
  
      /**
       * Gets a epoch associated with this das
       * @param timestamp The timestamp of the epoch
       * @param controller The view controller for the replicas
       * @return The epoch
       */
      public Epoch getEpoch(int timestamp, ServerViewController controller) {
          return getEpoch(timestamp,true, controller);
      }
  
      /**
       * Gets a epoch associated with this das
       * @param timestamp The number of the epoch
       * @param create if the epoch is to be created if not existent
       * @param controller The view controller for the replicas
       * @return The epoch
       */
      public Epoch getEpoch(int timestamp, boolean create, ServerViewController controller) {
          epochsLock.lock();
  
          Epoch epoch = epochs.get(timestamp);
          if(epoch == null && create){
              epoch = new Epoch(controller, this, timestamp);
              epochs.put(timestamp, epoch);
          }
  
          epochsLock.unlock();
  
          return epoch;
      }
      
      /**
       * Increments the ETS of this das, thus advancing
       * to the next epoch
       */
      public void incEts() {
          ets++;
      }
      
      /**
       * Increments the ETS of this das, thus advancing
       * to the next epoch
       * 
       * @param ets New ETS for this das, to advance
       * to the next epoch. It must be greater than the current ETS
       */
      public void setETS(int ets) {
          
          if (ets > this.ets) this.ets = ets;
      }
      
      /**
       * Returns the timestamp for the current epoch
       * @return the timestamp for the current epoch
       */
      public int getEts() {
          return ets;
      }
      
      /**
       * Store the value read from a Byzantine quorum of WRITES
       * @param value
       */
      public void setQuorumWrites(byte[] value) {
  
          quorumWrites = new TimestampValuePair(ets, value);
      }
  
      /**
       * Return the value read from a Byzantine quorum of WRITES that has
       * previously been stored
       * @return the value read from a Byzantine quorum of WRITES, if such
       * value has been obtained already
       */
      public TimestampValuePair getQuorumWrites() {
          return quorumWrites;
      }
  
      /**
       * Add a value that shall be written to the writeSet
       * @param value Value to write to the writeSet
       */
      public void addWritten(byte[] value) {
  
          writeSetLock.lock();
          writeSet.add(new TimestampValuePair(ets, value));
          writeSetLock.unlock();
      }
  
      /**
       * Remove an already writte value from  writeSet
       * @param value valor a remover do writeSet
       */
      public void removeWritten(byte[] value) {
  
          writeSetLock.lock();
          
          Set<TimestampValuePair> temp = (HashSet<TimestampValuePair>) writeSet.clone();
          
          for (TimestampValuePair rv : temp) {
  
              if (Arrays.equals(rv.getValue(), value)) writeSet.remove(rv);
          }
          writeSetLock.unlock();
  
      }
      public HashSet<TimestampValuePair> getWriteSet() {
          return (HashSet<TimestampValuePair>) writeSet.clone(); 
      }
      /**
       * Creates an epoch associated with this das, with the specified timestamp
       * @param timestamp The timestamp to associated to this epoch
       * @param recManager The replica's ServerViewController
       * @return The epoch
       */
      public Epoch createEpoch(int timestamp, ServerViewController recManager) {
          epochsLock.lock();
  
          Epoch epoch = new Epoch(recManager, this, timestamp);
          epochs.put(timestamp, epoch);
  
          epochsLock.unlock();
  
          return epoch;
      }
      /**
       * Creates a epoch associated with this das, supposedly the next
       * @param recManager The replica's ServerViewController
       * @return The epoch
       */
      public Epoch createEpoch(ServerViewController recManager) {
          epochsLock.lock();
  
          Set<Integer> keys = epochs.keySet();
  
          int max = -1;
          for (int k : keys) {
              if (k > max) max = k;
          }
  
          max++;
          Epoch epoch = new Epoch(recManager, this, max);
          epochs.put(max, epoch);
  
          epochsLock.unlock();
  
          return epoch;
      }
  
      /**
       * Removes epochs greater than 'limit' from this das instance
       *
       * @param limit Epochs that should be kept (from 0 to 'limit')
       */
      public void removeEpochs(int limit) {
          epochsLock.lock();
  
          for(Integer key : (Integer[])epochs.keySet().toArray(new Integer[0])) {
              if(key > limit) {
                  Epoch epoch = epochs.remove(key);
                  epoch.setRemoved();
                  //epoch.getTimeoutTask().cancel();
              }
          }
  
          epochsLock.unlock();
      }
  
      /**
       * The epoch at which a decision was possible to make
       * @return Epoch at which a decision was possible to make
       */
      public Epoch getDecisionEpoch() {
          epochsLock.lock();
          Epoch e = epochs.get(decisionEpoch);
          epochsLock.unlock();
          return e;
      }
  
      /**
       * The last epoch of this das instance
       *
       * @return Last epoch of this das instance
       */
      public Epoch getLastEpoch() {
          epochsLock.lock();
          if (epochs.isEmpty()) {
              epochsLock.unlock();
              return null;
          }
          //Epoch epoch = epochs.get(epochs.size() - 1);
          Epoch epoch = epochs.get(ets); // the last epoch corresponds to the current ETS
          epochsLock.unlock();
          return epoch;
      }
  
      /**
       * Informs whether or not the das instance has decided a value
       *
       * @return True if it is decided, false otherwise
       */
      public boolean isDecided() {
          return decided;
      }
  
      /**
       * Called by the Acceptor object, to set the decided value
       *
       * @param epoch The epoch at which a decision was made
       * @param deliver Set to true to deliver decision to TOMLayer/DeliveryThread
       */
      public void decided(Epoch epoch, boolean deliver) {
          if (!decided) {
              decided = true;
              decisionEpoch = epoch.getTimestamp();
              decision.setDecisionEpoch(epoch);
              if (deliver) {
                  logger.info("(Consensus.decided) Delivering decision from das " + getId() + " to the TOMLayer/DeliveryThread");
                  manager.getTOMLayer().decided(decision);
              }
          }
      }
  }
  