Some fiddling to handle cases where peers become connected after having

been disconnected (in which case there may be conflicts in lock 
ownership) or are connected asymmetrically (A is subscribed to B, B is 
not yet subscribed to A).


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4674 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/java/com/threerings/presents/peer/server/PeerManager.java

@@ -90,6 +90,18 @@ public class PeerManager
         public void changedCacheData (Streamable data);
     }
 
+    /**
+     * Used by entities that wish to know when this peer has been forced into immediately releasing
+     * a lock.
+     */
+    public static interface DroppedLockObserver
+    {
+        /**
+         * Called when this node has been forced to drop a lock.
+         */
+        public void droppedLock (Lock lock);
+    }
+
     /**
      * Creates a peer manager which will create a {@link NodeRepository} which will be used to
      * publish our existence and discover the other nodes.
@@ -191,7 +203,20 @@ public class PeerManager
         // clear out our client observer registration
         PresentsServer.clmgr.removeClientObserver(this);
 
-        // TODO: clear our record from the node table
+        // clear our record from the node table
+        _invoker.postUnit(new Invoker.Unit() {
+            public boolean invoke () {
+                try {
+                    _noderepo.deleteNode(_nodeName);
+                } catch (PersistenceException pe) {
+                    log.warning("Failed to delete node record [nodeName=" + _nodeName +
+                                ", error=" + pe + "].");
+                }
+                return false;
+            }
+        });
+
+        // shut down the peers
         for (PeerNode peer : _peers.values()) {
             peer.shutdown();
         }
@@ -407,6 +432,22 @@ public class PeerManager
         return null;
     }
 
+    /**
+     * Adds an observer to notify when this peer has been forced to drop a lock immediately.
+     */
+    public void addDroppedLockObserver (DroppedLockObserver observer)
+    {
+        _dropobs.add(observer);
+    }
+
+    /**
+     * Removes a dropped lock observer from the list.
+     */
+    public void removeDroppedLockObserver (DroppedLockObserver observer)
+    {
+        _dropobs.remove(observer);
+    }
+
     // documentation inherited from interface PeerProvider
     public void ratifyLockAction (ClientObject caller, Lock lock, boolean acquire)
     {
@@ -611,6 +652,19 @@ public class PeerManager
         });
     }
 
+    /**
+     * Called when we have been forced to drop a lock.
+     */
+    protected void droppedLock (final Lock lock)
+    {
+        _dropobs.apply(new ObserverList.ObserverOp<DroppedLockObserver>() {
+            public boolean apply (DroppedLockObserver observer) {
+                observer.droppedLock(lock);
+                return true;
+            }
+        });
+    }
+
     /**
      * Initializes the supplied client info for the supplied client.
      */
@@ -627,6 +681,15 @@ public class PeerManager
         return new PeerNode(record);
     }
 
+    /**
+     * Determines whether the first node named has priority over the second when resolving
+     * lock disputes.
+     */
+    protected static boolean hasPriority (String nodeName1, String nodeName2)
+    {
+        return nodeName1.compareTo(nodeName2) < 0;
+    }
+
     /**
      * Contains all runtime information for one of our peer nodes.
      */
@@ -664,7 +727,7 @@ public class PeerManager
 
             // if our client hasn't updated its record since we last tried to logon, then just
             // chill
-            if (_lastConnectStamp > record.lastUpdated.getTime()) {
+            if ((_lastConnectStamp - record.lastUpdated.getTime()) > STALE_INTERVAL) {
                 log.fine("Not reconnecting to stale client [record=" + _record +
                          ", lastTry=" + new Date(_lastConnectStamp) + "].");
                 return;
@@ -739,6 +802,7 @@ public class PeerManager
                     handler.clientDidLogoff();
                 }
             }
+            nodeobj = null;
         }
 
         // documentation inherited from interface ClientObserver
@@ -752,6 +816,22 @@ public class PeerManager
         {
             nodeobj = object;
 
+            // check for lock conflicts
+            for (Lock lock : nodeobj.locks) {
+                LockHandler handler = _locks.get(lock);
+                if (handler != null) {
+                    log.warning("Client hijacked lock in process of resolution [handler=" +
+                        handler + ", node=" + _record.nodeName + "].");
+                    handler.clientHijackedLock(_record.nodeName);
+
+                } else if (_nodeobj.locks.contains(lock)) {
+                    log.warning("Client hijacked lock owned by this node [lock=" + lock +
+                        ", node=" + _record.nodeName + "].");
+                    _nodeobj.removeFromLocks(lock);
+                    droppedLock(lock);
+                }
+            }
+
             // listen for lock and cache updates
             nodeobj.addListener(this);
         }
@@ -771,14 +851,14 @@ public class PeerManager
                 Lock lock = nodeobj.acquiringLock;
                 LockHandler handler = _locks.get(lock);
                 if (handler == null) {
+                    if (_nodeobj.locks.contains(lock)) {
+                        log.warning("Peer trying to acquire lock owned by this node [lock=" +
+                            lock + ", node=" + _record.nodeName + "].");
+                        return;
+                    }
                     handler = new LockHandler(this, lock, true);
                 } else {
-                    int val = handler.getNodeName().compareTo(_record.nodeName);
+                    if (hasPriority(handler.getNodeName(), _record.nodeName)) {
-                    if (val < 0) {
-                        return; // existing handler has priority
-                    } else if (val == 0) {
-                        log.warning("Received duplicate acquire request [handler=" +
-                            handler + "].");
                         return;
                     }
                     // this node has priority, so cancel the existing handler and take over
@@ -786,7 +866,7 @@ public class PeerManager
                     ResultListenerList<String> olisteners = handler.listeners;
                     handler.cancel();
                     handler = new LockHandler(this, lock, true);
-                    handler.listeners.addAll(olisteners);
+                    handler.listeners = olisteners;
                 }
                 _locks.put(lock, handler);
 
@@ -917,6 +997,17 @@ public class PeerManager
             listeners.requestCompleted(null);
         }
 
+        /**
+         * Called when a client hijacks the lock by having it in its node object when it
+         * connects.
+         */
+        public void clientHijackedLock (String nodeName)
+        {
+            cancel();
+            _locks.remove(_lock);
+            listeners.requestCompleted(nodeName);
+        }
+
         /**
          * Cancels this handler, as another one will be taking its place.
          */
@@ -1023,9 +1114,16 @@ public class PeerManager
     protected HashMap<String, ObserverList<StaleCacheObserver>> _cacheobs =
         new HashMap<String, ObserverList<StaleCacheObserver>>();
 
+    /** Listeners for dropped locks. */
+    protected ObserverList<DroppedLockObserver> _dropobs =
+        new ObserverList<DroppedLockObserver>(ObserverList.FAST_UNSAFE_NOTIFY);
+
     /** Locks in the process of resolution. */
     protected HashMap<Lock, LockHandler> _locks = new HashMap<Lock, LockHandler>();
 
+    /** The amount of time after which a node record can be considered out of date and invalid. */
+    protected static final long STALE_INTERVAL = 5L * 60L * 1000L;
+
     /** We wait this long for peer ratification to complete before acquiring/releasing the lock. */
     protected static final long LOCK_TIMEOUT = 5000L;
 }

src/java/com/threerings/presents/peer/server/persist/NodeRecord.java

@@ -60,6 +60,12 @@ public class NodeRecord
         this.port = port;
     }
 
+    /** Used for queries. */
+    public NodeRecord (String nodeName)
+    {
+        this.nodeName = nodeName;
+    }
+
     /**
      * Generates a string representation of this instance.
      */

src/java/com/threerings/presents/peer/server/persist/NodeRepository.java

@@ -73,6 +73,15 @@ public class NodeRepository extends JORARepository
         store(_ntable, record);
     }
 
+    /**
+     * Deletes the identified node record.
+     */
+    public void deleteNode (String nodeName)
+        throws PersistenceException
+    {
+        delete(_ntable, new NodeRecord(nodeName));
+    }
+
     @Override // documentation inherited
     protected void migrateSchema (Connection conn, DatabaseLiaison liaison)
         throws SQLException, PersistenceException