Instead of sync on PersistentMemberManager using CopyOnWrite structure

  There was a deadlock with revoke and unblock where revoke was taking
  lock on PersistentMemberManager and then requires lock on PersistenceAdvisorImpl.
  The intialization thread takes lock PersistenceAdvisorImpl and then to check
  whether the diskid is unblocked and requires lock on PersistentmemberManager

Author: Suranjan Kumar

gemfire-core/src/main/java/com/gemstone/gemfire/internal/cache/persistence/PersistentMemberManager.java

@@ -30,6 +30,7 @@
 import com.gemstone.gemfire.distributed.internal.ProfileListener;
 import com.gemstone.gemfire.distributed.internal.membership.InternalDistributedMember;
 import com.gemstone.gemfire.i18n.LogWriterI18n;
+import com.gemstone.gemfire.internal.CopyOnWriteHashSet;
 import com.gemstone.gemfire.internal.cache.GemFireCacheImpl;
 import com.gemstone.gemfire.internal.i18n.LocalizedStrings;
 import com.gemstone.gemfire.internal.util.TransformUtils;
@@ -47,7 +48,7 @@ public class PersistentMemberManager {
   private Map<PersistentMemberPattern, PendingRevokeListener> pendingRevokes 
       = new HashMap<PersistentMemberPattern, PendingRevokeListener>();
 
-  private final Set<PersistentMemberPattern> doNotWait = new HashSet();
+  private final Set<PersistentMemberPattern> doNotWait = new CopyOnWriteHashSet();
   private volatile boolean unblockNonHostingBuckets = false;
 
   private static final Object TOKEN = new Object();
@@ -69,7 +70,7 @@ public void revokeMember(PersistentMemberPattern pattern) {
   }
 
   public boolean doNotWaitOnMember(PersistentMemberID id) {
-    synchronized (this) {
+    if (this.unblockNonHostingBuckets) {
       for (PersistentMemberPattern p : this.doNotWait) {
         if (p.matches(id))
           return true;