hadoop 2.6.0 org.apache.hadoop.hdfs.server.blockmanagement。HeartbeatManager源代码分析

先分析HeartbeatManager的成员变量：

 datanodes存储的活着的datanodes;

 stats存储系统全局的一些统计信息。

/**
   * Stores a subset of the datanodeMap in DatanodeManager,
   * containing nodes that are considered alive.
   * The HeartbeatMonitor periodically checks for out-dated entries,
   * and removes them from the list.
   * It is synchronized by the heartbeat manager lock.
   */
  private final List datanodes = new ArrayList();

  /** Statistics, which are synchronized by the heartbeat manager lock. */
  private final Stats stats = new Stats();

  /** The time period to check for expired datanodes */
  private final long heartbeatRecheckInterval;
  /** Heartbeat monitor thread */
  private final Daemon heartbeatThread = new Daemon(new Monitor());

    
  final Namesystem namesystem;
  final BlockManager blockManager;

Stat内部类，存储Datanode的一些统计信息，对于decommissioning或者decommissioned的结点，只计算其used capacity.

/** Datanode statistics.
   * For decommissioning/decommissioned nodes, only used capacity is counted.
   */
  private static class Stats {
    private long capacityTotal = 0L;
    private long capacityUsed = 0L;
    private long capacityRemaining = 0L;
    private long blockPoolUsed = 0L;
    private int xceiverCount = 0;
    private long cacheCapacity = 0L;
    private long cacheUsed = 0L;

    private int nodesInService = 0;
    private int nodesInServiceXceiverCount = 0;

    private int expiredHeartbeats = 0;

    private void add(final DatanodeDescriptor node) {
      capacityUsed += node.getDfsUsed();
      blockPoolUsed += node.getBlockPoolUsed();
      xceiverCount += node.getXceiverCount();
      if (!(node.isDecommissionInProgress() || node.isDecommissioned())) {
        nodesInService++;
        nodesInServiceXceiverCount += node.getXceiverCount();
        capacityTotal += node.getCapacity();
        capacityRemaining += node.getRemaining();
      } else {
        capacityTotal += node.getDfsUsed();
      }
      cacheCapacity += node.getCacheCapacity();
      cacheUsed += node.getCacheUsed();
    }

    private void subtract(final DatanodeDescriptor node) {
      capacityUsed -= node.getDfsUsed();
      blockPoolUsed -= node.getBlockPoolUsed();
      xceiverCount -= node.getXceiverCount();
      if (!(node.isDecommissionInProgress() || node.isDecommissioned())) {
        nodesInService--;
        nodesInServiceXceiverCount -= node.getXceiverCount();
        capacityTotal -= node.getCapacity();
        capacityRemaining -= node.getRemaining();
      } else {
        capacityTotal -= node.getDfsUsed();
      }
      cacheCapacity -= node.getCacheCapacity();
      cacheUsed -= node.getCacheUsed();
    }
    
    /** Increment expired heartbeat counter. */
    private void incrExpiredHeartbeats() {
      expiredHeartbeats++;
    }
  }

heartbeatThread线程类的实现类是Monitor,代码如下：

/** Periodically check heartbeat and update block key */
  private class Monitor implements Runnable {
    private long lastHeartbeatCheck;
    private long lastBlockKeyUpdate;

    @Override
    public void run() {
      while(namesystem.isRunning()) {
        try {
          final long now = Time.now();
          if (lastHeartbeatCheck + heartbeatRecheckInterval < now) {
            heartbeatCheck();
            lastHeartbeatCheck = now;
          }
          if (blockManager.shouldUpdateBlockKey(now - lastBlockKeyUpdate)) {
            synchronized(HeartbeatManager.this) {
              for(DatanodeDescriptor d : datanodes) {
                d.needKeyUpdate = true;
              }
            }
            lastBlockKeyUpdate = now;
          }
        } catch (Exception e) {
          LOG.error("Exception while checking heartbeat", e);
        }
        try {
          Thread.sleep(5000);  // 5 seconds
        } catch (InterruptedException ie) {
        }
      }
    }
  }

在些线程中，周期性的调用heartbeatCheck方法,代码如下：

/**
   * Check if there are any expired heartbeats, and if so,
   * whether any blocks have to be re-replicated.
   * While removing dead datanodes, make sure that only one datanode is marked
   * dead at a time within the synchronized section. Otherwise, a cascading
   * effect causes more datanodes to be declared dead.
   * Check if there are any failed storage and if so,
   * Remove all the blocks on the storage. It also covers the following less
   * common scenarios. After DatanodeStorage is marked FAILED, it is still
   * possible to receive IBR for this storage.
   * 1) DN could deliver IBR for failed storage due to its implementation.
   *    a) DN queues a pending IBR request.
   *    b) The storage of the block fails.
   *    c) DN first sends HB, NN will mark the storage FAILED.
   *    d) DN then sends the pending IBR request.
   * 2) SBN processes block request from pendingDNMessages.
   *    It is possible to have messages in pendingDNMessages that refer
   *    to some failed storage.
   *    a) SBN receives a IBR and put it in pendingDNMessages.
   *    b) The storage of the block fails.
   *    c) Edit log replay get the IBR from pendingDNMessages.
   * Alternatively, we can resolve these scenarios with the following approaches.
   * A. Make sure DN don't deliver IBR for failed storage.
   * B. Remove all blocks in PendingDataNodeMessages for the failed storage
   *    when we remove all blocks from BlocksMap for that storage.
   */
  void heartbeatCheck() {
    final DatanodeManager dm = blockManager.getDatanodeManager();
    // It's OK to check safe mode w/o taking the lock here, we re-check
    // for safe mode after taking the lock before removing a datanode.
    if (namesystem.isInStartupSafeMode()) {
      return;
    }
    boolean allAlive = false;
    while (!allAlive) {
      // locate the first dead node.
      DatanodeID dead = null;

      // locate the first failed storage that isn't on a dead node.
      DatanodeStorageInfo failedStorage = null;

      // check the number of stale nodes
      int numOfStaleNodes = 0;
      int numOfStaleStorages = 0;
      synchronized(this) {
        for (DatanodeDescriptor d : datanodes) {
          if (dead == null && dm.isDatanodeDead(d)) {
            stats.incrExpiredHeartbeats();
            dead = d;
          }
          if (d.isStale(dm.getStaleInterval())) {
            numOfStaleNodes++;
          }
          DatanodeStorageInfo[] storageInfos = d.getStorageInfos();
          for(DatanodeStorageInfo storageInfo : storageInfos) {
            if (storageInfo.areBlockContentsStale()) {
              numOfStaleStorages++;
            }

            if (failedStorage == null &&
                storageInfo.areBlocksOnFailedStorage() &&
                d != dead) {
              failedStorage = storageInfo;
            }
          }

        }
        
        // Set the number of stale nodes in the DatanodeManager
        dm.setNumStaleNodes(numOfStaleNodes);
        dm.setNumStaleStorages(numOfStaleStorages);
      }

      allAlive = dead == null && failedStorage == null;
      if (dead != null) {
        // acquire the fsnamesystem lock, and then remove the dead node.
        namesystem.writeLock();
        try {
          if (namesystem.isInStartupSafeMode()) {
            return;
          }
          synchronized(this) {
            dm.removeDeadDatanode(dead);
          }
        } finally {
          namesystem.writeUnlock();
        }
      }
      if (failedStorage != null) {
        // acquire the fsnamesystem lock, and remove blocks on the storage.
        namesystem.writeLock();
        try {
          if (namesystem.isInStartupSafeMode()) {
            return;
          }
          synchronized(this) {
            blockManager.removeBlocksAssociatedTo(failedStorage);
          }
        } finally {
          namesystem.writeUnlock();
        }
      }
    }
  }