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/*
 * Copyright (c) 2010-2015 Pivotal Software, Inc. All rights reserved.
 *
 * 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. See accompanying
 * LICENSE file.
 */
/**
 * 
 */
package com.gemstone.gemfire.internal.cache;

import java.util.ConcurrentModificationException;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicLong;

import com.gemstone.gemfire.CancelException;
import com.gemstone.gemfire.SystemFailure;
import com.gemstone.gemfire.cache.util.ObjectSizer;
import com.gemstone.gemfire.i18n.LogWriterI18n;
import com.gemstone.gemfire.internal.GemFireVersion;
import com.gemstone.gemfire.internal.LogWriterImpl;
import com.gemstone.gemfire.internal.cache.control.MemoryEvent;
import com.gemstone.gemfire.internal.cache.control.ResourceListener;
import com.gemstone.gemfire.internal.cache.versions.CompactVersionHolder;
import com.gemstone.gemfire.internal.cache.versions.VersionSource;
import com.gemstone.gemfire.internal.cache.versions.VersionTag;
import com.gemstone.gemfire.internal.i18n.LocalizedStrings;
import com.gemstone.gemfire.internal.size.ReflectionSingleObjectSizer;
import com.gemstone.gemfire.internal.util.concurrent.StoppableReentrantLock;

/**
 * Tombstones are region entries that have been destroyed but are held
 * for future concurrency checks.  They are timed out after a reasonable
 * period of time when there is no longer the possibility of concurrent
 * modification conflicts.
 * 

 * The cache holds a tombstone service that is responsible for tracking
 * and timing out tombstones.
 * 
 * @author bruce
 */
public class TombstoneService  implements ResourceListener {
  /**
   * The default tombstone expiration period, in milliseconds for replicated
   * regions.
  This is the period over which the destroy operation may
   * conflict with another operation.  After this timeout elapses the tombstone
   * is put into a GC set for removal.  Removal is typically triggered by
   * the size of the GC set, but could be influenced by resource managers.
   * 
   * The default is 600,000 milliseconds (10 minutes).
   */
  public static long REPLICATED_TOMBSTONE_TIMEOUT = Long.getLong(
      "gemfire.tombstone-timeout", 600000L).longValue();
  
  /**
   * The default tombstone expiration period in millis for non-replicated
   * regions.  This tombstone timeout should be shorter than the one for
   * replicated regions and need not be excessively long.  Making it longer
   * than the replicated timeout can cause non-replicated regions to issue
   * revisions based on the tombstone that could overwrite modifications made
   * by others that no longer have the tombstone.

   * The default is 480,000 milliseconds (8 minutes)
   */
  public static long CLIENT_TOMBSTONE_TIMEOUT = Long.getLong(
      "gemfire.non-replicated-tombstone-timeout", 480000);
  
  /**
   * The max number of tombstones in an expired batch.  This covers
   * all replicated regions, including PR buckets.  The default is
   * 100,000 expired tombstones.
   */
  public static long EXPIRED_TOMBSTONE_LIMIT = Long.getLong("gemfire.tombstone-gc-threshold", 100000);
  
  /**
   * The interval to scan for expired tombstones in the queues
   */
  public static long DEFUNCT_TOMBSTONE_SCAN_INTERVAL = Long.getLong("gemfire.tombstone-scan-interval", 60000);
  
  /**
   * The threshold percentage of free max memory that will trigger tombstone GCs.
   * The default percentage is somewhat less than the LRU Heap evictor so that
   * we evict tombstones before we start evicting cache data.
   */
  public static double GC_MEMORY_THRESHOLD = Integer.getInteger("gemfire.tombstone-gc-memory-threshold",
      30 /*100-HeapLRUCapacityController.DEFAULT_HEAP_PERCENTAGE*/) * 0.01;
  
  /** this is a test hook for causing the tombstone service to act as though free memory is low */
  public static boolean FORCE_GC_MEMORY_EVENTS = false;
  
  /** verbose tombstone logging for diagnosing tombstone problems */
  public static boolean VERBOSE = Boolean.getBoolean("gemfire.TombstoneService.VERBOSE");

  public final static Object debugSync = new Object();
  public final static boolean DEBUG_TOMBSTONE_COUNT = Boolean.getBoolean("gemfire.TombstoneService.DEBUG_TOMBSTONE_COUNT");

  public static boolean IDLE_EXPIRATION = false; // dunit test hook for forced batch expiration
  
  /**
   * tasks for cleaning up tombstones
   */
  private TombstoneSweeper replicatedTombstoneSweeper;
  private TombstoneSweeper nonReplicatedTombstoneSweeper;

  /** a tombstone service is tied to a cache */
  private GemFireCacheImpl cache;

  /**
   * two queues, one for replicated regions (including PR buckets) and one for
   * other regions.  They have different timeout intervals.
   */
  private Queue replicatedTombstones = new ConcurrentLinkedQueue();
  private Queue nonReplicatedTombstones = new ConcurrentLinkedQueue();

  private AtomicLong replicatedTombstoneQueueSize = new AtomicLong();
  private AtomicLong nonReplicatedTombstoneQueueSize = new AtomicLong();
  
  public Object blockGCLock = new Object();
  private int progressingDeltaGIICount; 
  
  public static TombstoneService initialize(GemFireCacheImpl cache) {
    TombstoneService instance = new TombstoneService(cache);
//    cache.getResourceManager().addResourceListener(instance);  experimental
    return instance;
  }
  
  private TombstoneService(GemFireCacheImpl cache) {
    this.cache = cache;
    this.replicatedTombstoneSweeper = new TombstoneSweeper(cache, this.replicatedTombstones,
        REPLICATED_TOMBSTONE_TIMEOUT, true, this.replicatedTombstoneQueueSize);
    this.nonReplicatedTombstoneSweeper = new TombstoneSweeper(cache, this.nonReplicatedTombstones,
        CLIENT_TOMBSTONE_TIMEOUT, false, this.nonReplicatedTombstoneQueueSize);
    startSweeper(this.replicatedTombstoneSweeper);
    startSweeper(this.nonReplicatedTombstoneSweeper);
  }

  private void startSweeper(TombstoneSweeper tombstoneSweeper) {
    synchronized(tombstoneSweeper) {
      if (tombstoneSweeper.sweeperThread == null) {
        tombstoneSweeper.sweeperThread = new Thread(LogWriterImpl.createThreadGroup("Destroyed Entries Processors",
            cache.getLoggerI18n()), tombstoneSweeper);
        tombstoneSweeper.sweeperThread.setDaemon(true);
        String product = GemFireVersion.getProductName();
        if (tombstoneSweeper == this.replicatedTombstoneSweeper) {
          tombstoneSweeper.sweeperThread.setName(product + " Garbage Collection Thread 1");
        } else {
          tombstoneSweeper.sweeperThread.setName(product + " Garbage Collection Thread 2");
        }
        tombstoneSweeper.sweeperThread.start();
      }
    }
  }
  
  /**
   * this ensures that the background sweeper thread is stopped
   */
  public void stop() {
    stopSweeper(this.replicatedTombstoneSweeper);
    stopSweeper(this.nonReplicatedTombstoneSweeper);
  }
  
  private void stopSweeper(TombstoneSweeper t) {
    Thread sweeperThread;
    synchronized(t) {
      sweeperThread = t.sweeperThread;
      t.isStopped = true;
      if (sweeperThread != null) {
        t.notifyAll();
      }
    }
    try {
      sweeperThread.join(100);
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
    }
    t.tombstones.clear();
  }
  
  /**
   * Tombstones are markers placed in destroyed entries in order to keep the
   * entry around for a while so that it's available for concurrent modification
   * detection.
   * 
   * @param r  the region holding the entry
   * @param entry the region entry that holds the tombstone
   * @param destroyedVersion the version that was destroyed
   */
  public void scheduleTombstone(LocalRegion r, RegionEntry entry, VersionTag destroyedVersion) {
    boolean useReplicated = useReplicatedQueue(r);
    Tombstone ts = new Tombstone(entry, r, destroyedVersion);
    if (useReplicated) {
      this.replicatedTombstones.add(ts);
      this.replicatedTombstoneQueueSize.addAndGet(ts.getSize());
    } else {
      this.nonReplicatedTombstones.add(ts);
      this.nonReplicatedTombstoneQueueSize.addAndGet(ts.getSize());
    }
  }
  
  
  private boolean useReplicatedQueue(LocalRegion r) {
    return (r.getServerProxy() == null) && r.dataPolicy.withReplication();
  }
  
  
  /**
   * remove all tombstones for the given region.  Do this when the region is
   * cleared or destroyed.
   * @param r
   */
  public void unscheduleTombstones(LocalRegion r) {
//    long start = 0;
//    if (cache.getLoggerI18n().fineEnabled()) {
//      start = System.currentTimeMillis();
//    }
    Queue queue =
      r.getAttributes().getDataPolicy().withReplication() ? replicatedTombstones : nonReplicatedTombstones;
    long removalSize = 0;
    for (Iterator it=queue.iterator(); it.hasNext(); ) {
      Tombstone t = it.next();
      if (t.region == r) {
        it.remove();
        removalSize += t.getSize();
      }
    }
    if (queue == replicatedTombstones) {
      replicatedTombstoneQueueSize.addAndGet(-removalSize);
    } else {
      nonReplicatedTombstoneQueueSize.addAndGet(-removalSize);
    }
//    if (cache.getLoggerI18n().fineEnabled()) {
//      long end = System.currentTimeMillis();
//      if ( (end-start) > 10000 ) {
//        cache.getLoggerI18n().fine("Tombstone removal for " + r.getName() + " took " + (end-start) + " ms");
//      }
//    }
  }
  
  public int getGCBlockCount() {
    synchronized(this.blockGCLock) {
      return this.progressingDeltaGIICount;
    }
  }
   
  public int incrementGCBlockCount() {
    synchronized(this.blockGCLock) {
      return ++this.progressingDeltaGIICount;
    }
  }
  
  public int decrementGCBlockCount() {
    synchronized(this.blockGCLock) {
      return --this.progressingDeltaGIICount;
    }
  }
  
  /**
   * remove tombstones from the given region that have region-versions <= those in the given removal map
   * @return a collection of keys removed (only if the region is a bucket - empty otherwise)
   */
  public Set gcTombstones(LocalRegion r, Map regionGCVersions) {
    synchronized(this.blockGCLock) {
      int count = getGCBlockCount(); 
      if (count > 0) {
        // if any delta GII is on going as provider at this member, not to do tombstone GC
        LogWriterI18n log = cache.getLoggerI18n();
        if (log.fineEnabled()) {
          log.fine("gcTombstones skipped due to " + count + " Delta GII on going");
        }
        return null;
      }
    Queue queue;
    boolean replicated = false;
    long removalSize = 0;
    Tombstone currentTombstone;
    StoppableReentrantLock lock = null;
    boolean locked = false;
    if (r.getLogWriterI18n().fineEnabled()) {
      r.getLogWriterI18n().fine("gcTombstones invoked for region " + r + " and version map " + regionGCVersions);
    }
    Set removals = new HashSet();
    VersionSource myId = r.getVersionMember();
    boolean isBucket = r.isUsedForPartitionedRegionBucket();
    try {
      locked = false;
      if (r.getServerProxy() != null) {
        queue = this.nonReplicatedTombstones;
        lock = this.nonReplicatedTombstoneSweeper.currentTombstoneLock;
        lock.lock();
        locked = true;
        currentTombstone = this.nonReplicatedTombstoneSweeper.currentTombstone;
      } else {
        queue = this.replicatedTombstones;
        replicated = true;
        lock = this.replicatedTombstoneSweeper.currentTombstoneLock;
        lock.lock();
        locked = true;
        currentTombstone = this.replicatedTombstoneSweeper.currentTombstone;
      }
      if (currentTombstone != null && currentTombstone.region == r) {
        VersionSource destroyingMember = currentTombstone.getMemberID();
        if (destroyingMember == null) {
          destroyingMember = myId;
        }
        Long maxReclaimedRV = regionGCVersions.get(destroyingMember);
        if (maxReclaimedRV != null && currentTombstone.getRegionVersion() <= maxReclaimedRV.longValue()) {
          removals.add(currentTombstone);
        }
      }
      for (Tombstone t: queue) {
        if (t.region == r) {
          VersionSource destroyingMember = t.getMemberID();
          if (destroyingMember == null) {
            destroyingMember = myId;
          }
          Long maxReclaimedRV = regionGCVersions.get(destroyingMember);
          if (maxReclaimedRV != null && t.getRegionVersion() <= maxReclaimedRV.longValue()) {
            removals.add(t);
            removalSize += t.getSize();
          }
        }
      }
      
      queue.removeAll(removals);
      if (replicated) {
        this.replicatedTombstoneQueueSize.addAndGet(-removalSize);
      } else {
        this.nonReplicatedTombstoneQueueSize.addAndGet(-removalSize);
      }
    } finally {
      if (locked) {
        lock.unlock();
      }
    }
    
    //Record the GC versions now, so that we can persist them
    for(Map.Entry entry : regionGCVersions.entrySet()) {
      r.getVersionVector().recordGCVersion(entry.getKey(), entry.getValue());
    }
    
    //Remove any exceptions from the RVV that are older than the GC version
    r.getVersionVector().pruneOldExceptions();

    //Persist the GC RVV to disk. This needs to happen BEFORE we remove
    //the entries from map, to prevent us from removing a tombstone
    //from disk that has a version greater than the persisted
    //GV RVV.
    if(r.getDataPolicy().withPersistence()) {
      //Update the version vector which reflects what has been persisted on disk.
      r.getDiskRegion().writeRVVGC(r);
    }
    
    Set removedKeys = new HashSet();
    for (Tombstone t: removals) {
      if (t.region.getRegionMap().removeTombstone(t.entry, t, false, true) && isBucket) {
        removedKeys.add(t.entry.getKeyCopy());
      }
    }
    return removedKeys;
    } // sync on deltaGIILock
  }
  
  /**
   * client tombstone removal is key-based if the server is a PR.  This is due to the
   * server having separate version vectors for each bucket.  In the client this causes
   * the version vector to make no sense, so we have to send it a collection of the
   * keys removed on the server and then we brute-force remove any of them that
   * are tombstones on the client
   *  
   * @param r the region affected
   * @param tombstoneKeys the keys removed on the server
   */
  public void gcTombstoneKeys(LocalRegion r, Set tombstoneKeys) {
    Queue queue = this.nonReplicatedTombstones;
    Set removals = new HashSet();
    this.nonReplicatedTombstoneSweeper.currentTombstoneLock.lock();
    try {
      Tombstone currentTombstone = this.nonReplicatedTombstoneSweeper.currentTombstone;
      long removalSize = 0;
      VersionSource myId = r.getVersionMember();
      if (r.getLogWriterI18n().fineEnabled()) {
        r.getLogWriterI18n().fine("gcTombstones invoked for region " + r + " and keys " + tombstoneKeys);
      }
      if (currentTombstone != null && currentTombstone.region == r) {
        VersionSource destroyingMember = currentTombstone.getMemberID();
        if (destroyingMember == null) {
          destroyingMember = myId;
        }
        if (tombstoneKeys.contains(currentTombstone.entry.getKey())) {
          removals.add(currentTombstone);
        }
      }
      for (Tombstone t: queue) {
        if (t.region == r) {
          VersionSource destroyingMember = t.getMemberID();
          if (destroyingMember == null) {
            destroyingMember = myId;
          }
          if (tombstoneKeys.contains(t.entry.getKey())) {
            removals.add(t);
            removalSize += t.getSize();
          }
        }
      }
      
      queue.removeAll(removals);
      nonReplicatedTombstoneQueueSize.addAndGet(removalSize);
      
    } finally {
      this.nonReplicatedTombstoneSweeper.currentTombstoneLock.unlock();
    }
    
    for (Tombstone t: removals) {
      //TODO - RVV - to support persistent client regions
      //we need to actually record this as a destroy on disk, because
      //the GCC RVV doesn't make sense on the client.
      t.region.getRegionMap().removeTombstone(t.entry, t, false, true);
    }
  }
  
  /**
   * For test purposes only, force the expiration of a number of tombstones for
   * replicated regions.
   * @throws InterruptedException
   * @return true if the expiration occurred 
   */
  public boolean forceBatchExpirationForTests(int count) throws InterruptedException {
    this.replicatedTombstoneSweeper.testHook_batchExpired = new CountDownLatch(1);
    try {
      synchronized(this.replicatedTombstoneSweeper) {
        this.replicatedTombstoneSweeper.forceExpirationCount+= count;
        this.replicatedTombstoneSweeper.notifyAll();
      }

      //Wait for 30 seconds. If we wait longer, we risk hanging the tests if
      //something goes wrong.
      return this.replicatedTombstoneSweeper.testHook_batchExpired.await(30, TimeUnit.SECONDS);
    } finally {
      this.replicatedTombstoneSweeper.testHook_batchExpired=null;
    }
  }

  /**
   * Test Hook - slow operation
   * verify whether a tombstone is scheduled for expiration
   */
  public boolean isTombstoneScheduled(LocalRegion r, RegionEntry re) {
    Queue queue;
    if (r.getDataPolicy().withReplication()) {
      queue = this.replicatedTombstones;
    } else {
      queue = this.nonReplicatedTombstones;
    }
    VersionSource myId = r.getVersionMember();
    VersionTag entryTag = re.getVersionStamp().asVersionTag();
    int entryVersion = entryTag.getEntryVersion();
    for (Tombstone t: queue) {
      if (t.region == r) {
        VersionSource destroyingMember = t.getMemberID();
        if (destroyingMember == null) {
          destroyingMember = myId;
        }
        if (t.region == r
            && t.entry.getKey().equals(re.getKey())
            && t.getEntryVersion() == entryVersion) {
          return true;
        }
      }
    }
    if (this.replicatedTombstoneSweeper != null) {
      return this.replicatedTombstoneSweeper.hasExpiredTombstone(r, re, entryTag);
    }
    return false;
  }

  @Override
  public String toString() {
    return "Destroyed entries GC service.  Replicate Queue=" + this.replicatedTombstones.toString()
    + " Non-replicate Queue=" + this.nonReplicatedTombstones
    + (this.replicatedTombstoneSweeper.expiredTombstones != null?
        " expired batch size = " + this.replicatedTombstoneSweeper.expiredTombstones.size() : "");
  }  
  private static class Tombstone extends CompactVersionHolder {
    // tombstone overhead size
    public static int PER_TOMBSTONE_OVERHEAD = ReflectionSingleObjectSizer.REFERENCE_SIZE // queue's reference to the tombstone
      + ReflectionSingleObjectSizer.REFERENCE_SIZE * 3 // entry, region, member ID
      + ReflectionSingleObjectSizer.REFERENCE_SIZE  // region entry value (Token.TOMBSTONE)
      + 18; // version numbers and timestamp
    
    
    RegionEntry entry;
    LocalRegion region;
    
    Tombstone(RegionEntry entry, LocalRegion region, VersionTag destroyedVersion) {
      super(destroyedVersion);
      this.entry = entry;
      this.region = region;
    }
    
    public int getSize() {
      return Tombstone.PER_TOMBSTONE_OVERHEAD // includes per-entry overhead
        + ObjectSizer.DEFAULT.sizeof(entry.getRawKey());
    }
    
    @Override
    public String toString() {
      String v = super.toString();
      StringBuilder sb = new StringBuilder();
      sb.append("(").append(entry.getKeyCopy()).append("; ")
        .append(region.getName()).append("; ").append(v)
        .append(")");
      return sb.toString();
    }
  }
  
  private static class TombstoneSweeper implements Runnable {
    /**
     * the expiration time for tombstones in this sweeper
     */
    private final long expiryTime;
    /**
     * the current tombstones.  These are queued for expiration.  When tombstones
     * are resurrected they are left in this queue and the sweeper thread
     * figures out that they are no longer valid tombstones.
     */
    Queue tombstones;
    /**
     * The size, in bytes, of the queue
     */
    AtomicLong queueSize = new AtomicLong();
    /**
     * the thread that handles tombstone expiration.  It reads from the
     * tombstone queue.
     */
    Thread sweeperThread;
    /**
     * whether this sweeper accumulates expired tombstones for batch removal
     */
    boolean batchMode;
    /**
     * this suspends batch expiration.  It is intended for administrative use
     * so an operator can suspend the garbage-collection of tombstones for
     * replicated/partitioned regions if a persistent member goes off line
     */
    volatile boolean batchExpirationSuspended;
    /**
     * The sweeper thread's current tombstone
     */
    Tombstone currentTombstone;
    /**
     * a lock protecting the value of currentTombstone from changing
     */
    final StoppableReentrantLock currentTombstoneLock;
    /**
     * tombstones that have expired and are awaiting batch removal.  This
     * variable is only accessed by the sweeper thread and so is not guarded
     */
    Set expiredTombstones;
    
    /**
     * count of entries to forcibly expire due to memory events
     */
    private long forceExpirationCount = 0;
    
    /**
     * Force batch expiration
     */
    private boolean forceBatchExpiration = false;
    
    /**
     * Is a batch expiration in progress?
     */
    private volatile boolean batchExpirationInProgress;
    
    /**
     * A test hook to force expiration of tombstones.
     * See @{link {@link TombstoneService#forceBatchExpirationForTests(int)}
     */
    private CountDownLatch testHook_batchExpired;

    /**
     * the cache that owns all of the tombstones in this sweeper
     */
    private GemFireCacheImpl cache;
    
    private volatile boolean isStopped;
    
    TombstoneSweeper(GemFireCacheImpl cache,
        Queue tombstones,
        long expiryTime,
        boolean batchMode,
        AtomicLong queueSize) {
      this.cache = cache;
      this.expiryTime = expiryTime;
      this.tombstones = tombstones;
      this.queueSize = queueSize;
      if (batchMode) {
        this.batchMode = true;
        this.expiredTombstones = new HashSet();
      }
      this.currentTombstoneLock = new StoppableReentrantLock(cache.getCancelCriterion());
    }
    
    /** stop tombstone removal for sweepers that have batchMode==true */
    @SuppressWarnings("unused")
    void suspendBatchExpiration() {
      this.batchExpirationSuspended = true;
    }
    
    
    /** enables tombstone removal for sweepers that have batchMode==true */
    @SuppressWarnings("unused")
    void resumeBatchExpiration () {
      if (this.batchExpirationSuspended) {
        this.batchExpirationSuspended = false; // volatile write
      }
    }
    
    /** force a batch GC */
    void forceBatchExpiration() {
      this.forceBatchExpiration = true;
      //this.forceExpirationCount = EXPIRED_TOMBSTONE_LIMIT - this.expiredTombstones.size() + 1;
    }
    
    /** if we should GC the batched tombstones, this method will initiate the operation */
    private void processBatch() {
      if ((!batchExpirationSuspended &&
          (this.forceBatchExpiration || (this.expiredTombstones.size() >= EXPIRED_TOMBSTONE_LIMIT)))
        || testHook_batchExpired != null) {
        this.forceBatchExpiration = false;
        expireBatch();
      }
    }
    
    /** test hook - unsafe since not synchronized */
    boolean hasExpiredTombstone(LocalRegion r, RegionEntry re, VersionTag tag) {
      int entryVersion = tag.getEntryVersion();
      boolean retry;
      do {
        retry = false;
        try {
          for (Tombstone t: this.expiredTombstones) {
            if (t.region == r
                && t.entry.getKey().equals(re.getKey())
                && t.getEntryVersion() == entryVersion) {
              return true;
            }
          }
        } catch (ConcurrentModificationException e) {
          retry = true;
        }
      } while (retry);
      return false;
    }
    
    
    
    /** expire a batch of tombstones */
    private void expireBatch() {
      // fix for bug #46087 - OOME due to too many GC threads
      if (this.batchExpirationInProgress) {
        // incorrect return due to race between this and waiting-pool GC thread is okay
        // because the sweeper thread will just try again after its next sleep (max sleep is 10 seconds)
        return;
      }
      synchronized(cache.getTombstoneService().blockGCLock) {
        int count = cache.getTombstoneService().getGCBlockCount();
        if (count > 0) {
          // if any delta GII is on going as provider at this member, not to do tombstone GC
          LogWriterI18n log = cache.getLoggerI18n();
          if (log.fineEnabled()) {
            log.fine("expireBatch skipped due to " + count + " Delta GII on going");
          }
          return;
        }

      this.batchExpirationInProgress = true;
      boolean batchScheduled = false;
      try {
        final Set regionsAffected = new HashSet();
        Set expired = expiredTombstones;
        long removalSize = 0;
        expiredTombstones = new HashSet();
        if (expired.size() == 0) {
          return;
        }

        //Update the GC RVV for all of the affected regions.
        //We need to do this so that we can persist the GC RVV before
        //we start removing entries from the map.
        for (Tombstone t: expired) {
          t.region.getVersionVector().recordGCVersion(t.getMemberID(), t.getRegionVersion());
          regionsAffected.add((DistributedRegion)t.region);
        }
        
        for (DistributedRegion r: regionsAffected) {
          //Remove any exceptions from the RVV that are older than the GC version
          r.getVersionVector().pruneOldExceptions();

          //Persist the GC RVV to disk. This needs to happen BEFORE we remove
          //the entries from map, to prevent us from removing a tombstone
          //from disk that has a version greater than the persisted
          //GV RVV.
          if(r.getDataPolicy().withPersistence()) {
            r.getDiskRegion().writeRVVGC(r);
          }
        }

        final Map> reapedKeys = new HashMap>();
        
        //Remove the tombstones from the in memory region map.
        for (Tombstone t: expired) {
          // for PR buckets we have to keep track of the keys removed because clients have
          // them all lumped in a single non-PR region
          if (t.region.getRegionMap().removeTombstone(t.entry, t, false, true) && t.region.isUsedForPartitionedRegionBucket()) {
            Set keys = reapedKeys.get(t.region);
            if (keys == null) {
              keys = new HashSet();
              reapedKeys.put(t.region, keys);
            }
            keys.add(t.entry.getKeyCopy());
          }
          removalSize += t.getSize();
        }

        this.queueSize.addAndGet(-removalSize);
        // do messaging in a pool so this thread is not stuck trying to
        // communicate with other members
        cache.getDistributionManager().getWaitingThreadPool().execute(new Runnable() {
          public void run() {
            try {
              // this thread should not reference other sweeper state, which is not synchronized
              for (DistributedRegion r: regionsAffected) {
                r.distributeTombstoneGC(reapedKeys.get(r));
              }
            } finally {
              batchExpirationInProgress = false;
            }
          }
        });
        batchScheduled = true;
      } finally {
        if(testHook_batchExpired != null) {
          testHook_batchExpired.countDown();
        }
        if (!batchScheduled) {
          batchExpirationInProgress = false;
        }
      }
      } // sync on deltaGIILock
    }
    
    /**
     * The run loop picks a tombstone off of the expiration queue and waits
     * for it to expire.  It also periodically scans for resurrected tombstones
     * and handles batch expiration.  Batch expiration works by tossing the
     * expired tombstones into a set and delaying the removal of those tombstones
     * from the Region until scheduled points in the calendar.  
     */
    public void run() {
      long minimumRetentionMs = this.expiryTime / 10; // forceExpiration will not work on something younger than this
      long maximumSleepTime = 10000;
      LogWriterI18n log = cache.getLoggerI18n();
      if (VERBOSE) {
        log.info(LocalizedStrings.DEBUG,
            "Destroyed entries sweeper starting with default sleep interval="+this.expiryTime);
      }
      currentTombstone = null;
      // millis we need to run a scan of queue and batch set for resurrected tombstones
      long minimumScanTime = 100;
      // how often to perform the scan
      long scanInterval = Math.min(DEFUNCT_TOMBSTONE_SCAN_INTERVAL, expiryTime);
      long lastScanTime = this.cache.cacheTimeMillis();
      
      while (!isStopped && cache.getCancelCriterion().cancelInProgress() == null) {
        Throwable problem = null;
        try {
          if (this.batchMode) {
            cache.getCachePerfStats().setReplicatedTombstonesSize(queueSize.get());
          } else {
            cache.getCachePerfStats().setNonReplicatedTombstonesSize(queueSize.get());
          }
          SystemFailure.checkFailure();
          long now = this.cache.cacheTimeMillis();
          if (forceExpirationCount <= 0) {
            if (this.batchMode) {
              processBatch();
            }
            // if we're running out of memory we get a little more aggressive about
            // the size of the batch we'll expire
            if (GC_MEMORY_THRESHOLD > 0 && this.batchMode) {
              // check to see how we're doing on memory
              Runtime rt = Runtime.getRuntime();
              long freeMemory = rt.freeMemory();
              long totalMemory = rt.totalMemory();
              long maxMemory = rt.maxMemory();
              freeMemory += (maxMemory-totalMemory);
              if (FORCE_GC_MEMORY_EVENTS ||
                  freeMemory / (totalMemory * 1.0) < GC_MEMORY_THRESHOLD) {
                forceBatchExpiration = !this.batchExpirationInProgress &&
                       this.expiredTombstones.size() > (EXPIRED_TOMBSTONE_LIMIT / 4);
                if (forceBatchExpiration && cache.getLoggerI18n().fineEnabled()) {
                  cache.getLoggerI18n().fine("forcing batch expiration due to low memory conditions");
                }
                // forcing expiration of tombstones that have not timed out can cause inconsistencies
                // too easily
  //              if (this.batchMode) {
  //                forceExpirationCount = EXPIRED_TOMBSTONE_LIMIT - this.expiredTombstones.size();
  //              } else {
  //                forceExpirationCount = EXPIRED_TOMBSTONE_LIMIT;
  //              }
  //              if (VERBOSE || cache.getLoggerI18n().finerEnabled()) {
  //                cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "forcing expiration of " + forceExpirationCount + " tombstones due to memory constraints.  Free memory = " + freeMemory + " max memory = " + maxMemory);
  //              }
  //              maximumSleepTime = 1000;
              }
            }
          }
          if (currentTombstone == null) {
            try {
              currentTombstoneLock.lock();
              try {
                currentTombstone = tombstones.remove();
              } finally {
                currentTombstoneLock.unlock();
              }
              if (VERBOSE) {
                cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "current tombstone is " + currentTombstone);
              }
            } catch (NoSuchElementException e) {
              // expected
              if (VERBOSE) {
                cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "queue is empty - will sleep");
              }
              forceExpirationCount = 0;
            }
          }
          long sleepTime;
          if (currentTombstone == null) {
            sleepTime = expiryTime;
          } else if (currentTombstone.getVersionTimeStamp()+expiryTime > now && (forceExpirationCount <= 0 || (currentTombstone.getVersionTimeStamp() + expiryTime - now) <= minimumRetentionMs)) {
            sleepTime = currentTombstone.getVersionTimeStamp()+expiryTime - now;
          } else {
            if (forceExpirationCount > 0) {
              forceExpirationCount--;
            }
            sleepTime = 0;
            try {
              if (batchMode) {
                if (VERBOSE) {
                  cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "expiring tombstone " + currentTombstone);
                }
                expiredTombstones.add(currentTombstone);
              } else {
                if (VERBOSE) {
                  cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "removing expired tombstone " + currentTombstone);
                }
                queueSize.addAndGet(-currentTombstone.getSize());
                currentTombstone.region.getRegionMap().removeTombstone(currentTombstone.entry, currentTombstone, false, true);
              }
              currentTombstoneLock.lock();
              try {
                currentTombstone = null;
              } finally {
                currentTombstoneLock.unlock();
              }
            } catch (CancelException e) {
  //            cache.getLoggerI18n().warning(
  //                LocalizedStrings.GemFireCacheImpl_TOMBSTONE_ERROR, e);
              return;
            } catch (Exception e) {
              cache.getLoggerI18n().warning(
                  LocalizedStrings.GemFireCacheImpl_TOMBSTONE_ERROR, e);
            }
          }
          if (sleepTime > 0) {
            // initial sleeps could be very long, so we reduce the interval to allow
            // this thread to periodically sweep up tombstones for resurrected entries
            sleepTime = Math.min(sleepTime, scanInterval);
            if (sleepTime > minimumScanTime  &&  (now - lastScanTime) > scanInterval) {
              lastScanTime = now;
              long start = now;
              // see if any have been superseded
              for (Iterator it = tombstones.iterator(); it.hasNext(); ) {
                Tombstone test = it.next();
  //              cache.getLoggerI18n().severe(LocalizedStrings.DEBUG, "test="+test);
  //              cache.getLoggerI18n().severe(LocalizedStrings.DEBUG, "test.region="+test.region);
  //              cache.getLoggerI18n().severe(LocalizedStrings.DEBUG, "test.destroyedVersion="+test.destroyedVersion);
                if (it.hasNext()) {
                  if (test.region.getRegionMap().isTombstoneNotNeeded(test.entry, test.getEntryVersion())) {
                    it.remove();
                    this.queueSize.addAndGet(-test.getSize());
                    if (test == currentTombstone) {
                      currentTombstoneLock.lock();
                      try {
                        currentTombstone = null;
                      } finally {
                        currentTombstoneLock.unlock();
                      }
                      sleepTime = 0;
                    }
                  } else if (batchMode && test != currentTombstone && (test.getVersionTimeStamp()+expiryTime) <= now) {
                    it.remove();
                    this.queueSize.addAndGet(-test.getSize());
                    if (VERBOSE) {
                      cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "expiring tombstone " + currentTombstone);
                    }
                    expiredTombstones.add(test);
                    sleepTime = 0;
                  }
                }
              }
              // now check the batch of timed-out tombstones, if there is one
              if (batchMode) {
                for (Iterator it = expiredTombstones.iterator(); it.hasNext(); ) {
                  Tombstone test = it.next();
                  if (test.region.getRegionMap().isTombstoneNotNeeded(test.entry, test.getEntryVersion())) {
                    if (VERBOSE) {
                      cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "removing obsolete tombstone: " + test);
                    }
                    it.remove();
                    this.queueSize.addAndGet(-test.getSize());
                    if (test == currentTombstone) {
                      currentTombstoneLock.lock();
                      try {
                        currentTombstone = null;
                      } finally {
                        currentTombstoneLock.unlock();
                      }
                      sleepTime = 0;
                    }
                  }
                }
              }
              if (sleepTime > 0) {
                long elapsed = this.cache.cacheTimeMillis() - start;
                sleepTime = sleepTime - elapsed;
                if (sleepTime <= 0) {
                  minimumScanTime = elapsed;
                  continue;
                }
              }
            }
            if (sleepTime > 0) {
              try {
                sleepTime = Math.min(sleepTime, maximumSleepTime);
                if (VERBOSE) {
                  cache.getLoggerI18n().info(LocalizedStrings.DEBUG, "sleeping for " + sleepTime);
                }
                synchronized(this) {
                  if(isStopped) {
                    return;
                  }
                  this.wait(sleepTime);
                }
              } catch (InterruptedException e) {
                return;
              }
            }
          } // sleepTime > 0
        } catch (CancelException e) {
          break;
        } catch (VirtualMachineError err) { // GemStoneAddition
          SystemFailure.initiateFailure(err);
          // If this ever returns, rethrow the error.  We're poisoned
          // now, so don't let this thread continue.
          throw err;
        } catch (Throwable e) {
          SystemFailure.checkFailure();
          problem = e;
        }
        if (problem != null) {
          cache.getLoggerI18n().severe(LocalizedStrings.TombstoneService_UNEXPECTED_EXCEPTION, problem);
        }
      } // while()
    } // run()
    
  } // class TombstoneSweeper

  /* (non-Javadoc)
   * @see com.gemstone.gemfire.internal.cache.control.ResourceListener#onEvent(java.lang.Object)
   */
  @Override
  public void onEvent(MemoryEvent event) {
    if (event.isLocal()) {
      if (event.getState().isEviction() && !event.getPreviousState().isEviction()) {
        this.replicatedTombstoneSweeper.forceBatchExpiration();
      }
    }
  }


}
 















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