Added the ability to remove neighbours from the database (untested).

api/net/sf/briar/api/db/DatabaseComponent.java

@@ -50,6 +50,9 @@ public interface DatabaseComponent {
 	 */
 	void receiveBundle(NeighbourId n, Bundle b) throws DbException;
 
+	/** Removes a neighbour (and all associated state) from the database. */
+	void removeNeighbour(NeighbourId n) throws DbException;
+
 	/** Records the user's rating for the given author. */
 	void setRating(AuthorId a, Rating r) throws DbException;
 

components/net/sf/briar/db/Database.java

@@ -19,6 +19,16 @@ import net.sf.briar.api.protocol.MessageId;
  * obtained by calling startTransaction(). Every transaction must be
  * terminated by calling either abortTransaction() or commitTransaction(),
  * even if an exception is thrown.
+ * 
+ * Locking is provided by the DatabaseComponent implementation. To prevent
+ * deadlock, locks must be acquired in the following order:
+ * <ul>
+ * <li> contacts
+ * <li> messages
+ * <li> messageStatuses
+ * <li> ratings
+ * <li> subscriptions
+ * </ul>
  */
 interface Database<T> {
 
@@ -49,63 +59,80 @@ interface Database<T> {
 
 	/**
 	 * Records a received batch as needing to be acknowledged.
-	 * Locking: neighbours write.
+	 * <p>
+	 * Locking: contacts read, messageStatuses write.
 	 */
 	void addBatchToAck(T txn, NeighbourId n, BatchId b) throws DbException;
 
 	/**
 	 * Returns false if the given message is already in the database. Otherwise
 	 * stores the message and returns true.
+	 * <p>
 	 * Locking: messages write.
 	 */
 	boolean addMessage(T txn, Message m) throws DbException;
 
 	/**
 	 * Adds a new neighbour to the database.
-	 * Locking: neighbours write.
+	 * <p>
+	 * Locking: contacts write, messageStatuses write.
 	 */
 	void addNeighbour(T txn, NeighbourId n) throws DbException;
 
 	/**
 	 * Records a sent batch as needing to be acknowledged.
-	 * Locking: neighbours write, messages read.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses write.
 	 */
 	void addOutstandingBatch(T txn, NeighbourId n, BatchId b, Set<MessageId> sent) throws DbException;
 
 	/**
 	 * Records a received bundle. This should be called after processing the
 	 * bundle's contents, and may result in outstanding messages becoming
-	 * eligible for retransmittion.
+	 * eligible for retransmission.
-	 * Locking: neighbours write, messages read.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses write.
 	 */
 	Set<BatchId> addReceivedBundle(T txn, NeighbourId n, BundleId b) throws DbException;
 
 	/**
 	 * Subscribes to the given group.
+	 * <p>
 	 * Locking: subscriptions write.
 	 */
 	void addSubscription(T txn, GroupId g) throws DbException;
 
 	/**
 	 * Records a neighbour's subscription to a group.
-	 * Locking: neighbours write.
+	 * <p>
+	 * Locking: contacts read, messageStatuses write.
 	 */
 	void addSubscription(T txn, NeighbourId n, GroupId g) throws DbException;
 
 	/**
 	 * Removes all recorded subscriptions for the given neighbour.
-	 * Locking: neighbours write.
+	 * <p>
+	 * Locking: contacts read, messageStatuses write.
 	 */
 	void clearSubscriptions(T txn, NeighbourId n) throws DbException;
 
 	/**
 	 * Returns true iff the database contains the given message.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	boolean containsMessage(T txn, MessageId m) throws DbException;
 
+	/**
+	 * Returns true iff the database contains the given neighbour.
+	 * <p>
+	 * Locking: contacts read.
+	 */
+	boolean containsNeighbour(T txn, NeighbourId n) throws DbException;
+
 	/**
 	 * Returns true iff the user is subscribed to the given group.
+	 * <p>
 	 * Locking: subscriptions read.
 	 */
 	boolean containsSubscription(T txn, GroupId g) throws DbException;
@@ -114,18 +141,21 @@ interface Database<T> {
 	 * Returns the amount of free storage space available to the database, in
 	 * bytes. This is based on the minimum of the space available on the device
 	 * where the database is stored and the database's configured size.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	long getFreeSpace() throws DbException;
 
 	/**
 	 * Returns the message identified by the given ID.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	Message getMessage(T txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the IDs of all messages signed by the given author.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	Iterable<MessageId> getMessagesByAuthor(T txn, AuthorId a) throws DbException;
@@ -133,31 +163,36 @@ interface Database<T> {
 	/**
 	 * Returns the IDs of all children of the message identified by the given
 	 * ID that are present in the database.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	Iterable<MessageId> getMessagesByParent(T txn, MessageId m) throws DbException;
 
 	/**
-	 * Returns the IDs of all neighbours
+	 * Returns the IDs of all neighbours.
-	 * Locking: neighbours read.
+	 * <p>
+	 * Locking: contacts read, messageStatuses read.
 	 */
 	Set<NeighbourId> getNeighbours(T txn) throws DbException;
 
 	/**
 	 * Returns the IDs of the oldest messages in the database, with a total
 	 * size less than or equal to the given size.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	Iterable<MessageId> getOldMessages(T txn, long size) throws DbException;
 
 	/**
 	 * Returns the parent of the given message.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	MessageId getParent(T txn, MessageId m) throws DbException;
 
 	/**
 	 * Returns the user's rating for the given author.
+	 * <p>
 	 * Locking: ratings read.
 	 */
 	Rating getRating(T txn, AuthorId a) throws DbException;
@@ -166,6 +201,7 @@ interface Database<T> {
 	 * Returns the sendability score of the given message. Messages with
 	 * sendability scores greater than zero are eligible to be sent to
 	 * neighbours.
+	 * <p>
 	 * Locking: messages read.
 	 */
 	int getSendability(T txn, MessageId m) throws DbException;
@@ -173,12 +209,14 @@ interface Database<T> {
 	/**
 	 * Returns the IDs of some messages that are eligible to be sent to the
 	 * given neighbour, with a total size less than or equal to the given size.
-	 * Locking: neighbours read, messages read.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses read.
 	 */
 	Iterable<MessageId> getSendableMessages(T txn, NeighbourId n, long capacity) throws DbException;
 
 	/**
 	 * Returns the groups to which the user subscribes.
+	 * <p>
 	 * Locking: subscriptions read.
 	 */
 	Set<GroupId> getSubscriptions(T txn) throws DbException;
@@ -187,14 +225,16 @@ interface Database<T> {
 	 * Removes an outstanding batch that has been acknowledged. Any messages in
 	 * the batch that are still considered outstanding (Status.SENT) with
 	 * respect to the given neighbour are now considered seen (Status.SEEN).
-	 * Locking: neighbours write, messages read.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses write.
 	 */
 	void removeAckedBatch(T txn, NeighbourId n, BatchId b) throws DbException;
 
 	/**
 	 * Removes and returns the IDs of any batches received from the given
 	 * neighbour that need to be acknowledged.
-	 * Locking: neighbours write.
+	 * <p>
+	 * Locking: contacts read, messageStatuses write.
 	 */
 	Set<BatchId> removeBatchesToAck(T txn, NeighbourId n) throws DbException;
 
@@ -202,38 +242,52 @@ interface Database<T> {
 	 * Removes an outstanding batch that has been lost. Any messages in the
 	 * batch that are still considered outstanding (Status.SENT) with respect
 	 * to the given neighbour are now considered unsent (Status.NEW).
-	 * Locking: neighbours write, messages read.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses write.
 	 */
 	void removeLostBatch(T txn, NeighbourId n, BatchId b) throws DbException;
 
 	/**
-	 * Removes a message from the database.
+	 * Removes a message (and all associated state) from the database.
-	 * Locking: neighbours write, messages write.
+	 * <p>
+	 * Locking: contacts read, messages write, messageStatuses write.
 	 */
 	void removeMessage(T txn, MessageId m) throws DbException;
 
+	/**
+	 * Removes a neighbour (and all associated state) from the database.
+	 * <p>
+	 * Locking: contacts write, messageStatuses write.
+	 */
+	void removeNeighbour(T txn, NeighbourId n) throws DbException;
+
 	/**
 	 * Unsubscribes from the given group. Any messages belonging to the group
 	 * are deleted from the database.
-	 * Locking: subscriptions write, neighbours write, messages write.
+	 * <p>
+	 * Locking: contacts read, subscriptions write, messages write,
+	 * messageStatuses write.
 	 */
 	void removeSubscription(T txn, GroupId g) throws DbException;
 
 	/**
 	 * Records the user's rating for the given author.
+	 * <p>
 	 * Locking: ratings write.
 	 */
 	Rating setRating(T txn, AuthorId a, Rating r) throws DbException;
 
 	/**
 	 * Records the sendability score of the given message.
+	 * <p>
 	 * Locking: messages write.
 	 */
 	void setSendability(T txn, MessageId m, int sendability) throws DbException;
 
 	/**
 	 * Sets the status of the given message with respect to the given neighbour.
-	 * Locking: neighbours write, messages read
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses write.
 	 */
 	void setStatus(T txn, NeighbourId n, MessageId m, Status s) throws DbException;
 }

components/net/sf/briar/db/DatabaseComponentImpl.java

@@ -74,7 +74,20 @@ abstract class DatabaseComponentImpl<Txn> implements DatabaseComponent {
 		}
 	}
 
-	// Locking: messages write, neighbours write
+	// Locking: contacts read
+	protected boolean containsNeighbour(NeighbourId n) throws DbException {
+		Txn txn = db.startTransaction();
+		try {
+			boolean contains = db.containsNeighbour(txn, n);
+			db.commitTransaction(txn);
+			return contains;
+		} catch(DbException e) {
+			db.abortTransaction(txn);
+			throw e;
+		}
+	}
+
+	// Locking: contacts read, messages write, messageStatuses write
 	protected void removeMessage(Txn txn, MessageId id) throws DbException {
 		Integer sendability = db.getSendability(txn, id);
 		assert sendability != null;
@@ -127,7 +140,7 @@ abstract class DatabaseComponentImpl<Txn> implements DatabaseComponent {
 		new Thread(cleaner).start();
 	}
 
-	// Locking: messages write, neighbours write
+	// Locking: contacts read, messages write, messageStatuses write
 	protected boolean storeMessage(Txn txn, Message m, NeighbourId sender)
 	throws DbException {
 		boolean added = db.addMessage(txn, m);

components/net/sf/briar/db/JdbcDatabase.java

@@ -650,6 +650,33 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public boolean containsNeighbour(Connection txn, NeighbourId n)
+	throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT COUNT(neighbourId) FROM neighbours"
+				+ " WHERE neighbourId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, n.getInt());
+			rs = ps.executeQuery();
+			boolean found = rs.next();
+			assert found;
+			int count = rs.getInt(1);
+			assert count <= 1;
+			boolean more = rs.next();
+			assert !more;
+			rs.close();
+			ps.close();
+			return count > 0;
+		} catch(SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			tryToClose(txn);
+			throw new DbException(e);
+		}
+	}
+
 	public boolean containsSubscription(Connection txn, GroupId g)
 	throws DbException {
 		PreparedStatement ps = null;
@@ -1070,6 +1097,23 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public void removeNeighbour(Connection txn, NeighbourId n)
+	throws DbException {
+		PreparedStatement ps = null;
+		try {
+			String sql = "DELETE FROM neighbours WHERE neighbourId = ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, n.getInt());
+			int rowsAffected = ps.executeUpdate();
+			assert rowsAffected == 1;
+			ps.close();
+		} catch(SQLException e) {
+			tryToClose(ps);
+			tryToClose(txn);
+			throw new DbException(e);
+		}
+	}
+
 	public void removeSubscription(Connection txn, GroupId g)
 	throws DbException {
 		PreparedStatement ps = null;

components/net/sf/briar/db/ReadWriteLockDatabaseComponent.java

@@ -32,9 +32,11 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	 * implementation can allow writers to starve.
 	 */
 
+	private final ReentrantReadWriteLock contactLock =
+		new ReentrantReadWriteLock(true);
 	private final ReentrantReadWriteLock messageLock =
 		new ReentrantReadWriteLock(true);
-	private final ReentrantReadWriteLock neighbourLock =
+	private final ReentrantReadWriteLock messageStatusLock =
 		new ReentrantReadWriteLock(true);
 	private final ReentrantReadWriteLock ratingLock =
 		new ReentrantReadWriteLock(true);
@@ -48,9 +50,11 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	protected void expireMessages(long size) throws DbException {
+		contactLock.readLock().lock();
+		try {
 			messageLock.writeLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					Txn txn = db.startTransaction();
 					try {
@@ -63,17 +67,22 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						throw e;
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.writeLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 	}
 
 	public void close() throws DbException {
+		contactLock.writeLock().lock();
+		try {
 			messageLock.writeLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					ratingLock.writeLock().lock();
 					try {
@@ -87,16 +96,21 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						ratingLock.writeLock().unlock();
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.writeLock().unlock();
 			}
+		} finally {
+			contactLock.writeLock().unlock();
+		}
 	}
 
 	public void addNeighbour(NeighbourId n) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Adding neighbour " + n);
-		neighbourLock.writeLock().lock();
+		contactLock.writeLock().lock();
+		try {
+			messageStatusLock.writeLock().lock();
 			try {
 				Txn txn = db.startTransaction();
 				try {
@@ -107,15 +121,20 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			} finally {
-			neighbourLock.writeLock().unlock();
+				messageStatusLock.writeLock().unlock();
+			}
+		} finally {
+			contactLock.writeLock().unlock();
 		}
 	}
 
 	public void addLocallyGeneratedMessage(Message m) throws DbException {
 		waitForPermissionToWrite();
+		contactLock.readLock().lock();
+		try {
 			messageLock.writeLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					subscriptionLock.readLock().lock();
 					try {
@@ -137,11 +156,14 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						subscriptionLock.readLock().unlock();
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.writeLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 	}
 
 	public Rating getRating(AuthorId a) throws DbException {
@@ -161,6 +183,28 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		}
 	}
 
+	public void removeNeighbour(NeighbourId n) throws DbException {
+		if(LOG.isLoggable(Level.FINE)) LOG.fine("Removing neighbour " + n);
+		contactLock.writeLock().lock();
+		try {
+			messageStatusLock.writeLock().lock();
+			try {
+				Txn txn = db.startTransaction();
+				try {
+					db.removeNeighbour(txn, n);
+					db.commitTransaction(txn);
+				} catch(DbException e) {
+					db.abortTransaction(txn);
+					throw e;
+				}
+			} finally {
+				messageStatusLock.writeLock().unlock();
+			}
+		} finally {
+			contactLock.writeLock().unlock();
+		}
+	}
+
 	public void setRating(AuthorId a, Rating r) throws DbException {
 		messageLock.writeLock().lock();
 		try {
@@ -224,9 +268,11 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 
 	public void unsubscribe(GroupId g) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Unsubscribing from " + g);
+		contactLock.readLock().lock();
+		try {
 			messageLock.writeLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					subscriptionLock.writeLock().lock();
 					try {
@@ -242,17 +288,23 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						subscriptionLock.writeLock().unlock();
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.writeLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 	}
 
 	public void generateBundle(NeighbourId n, Bundle b) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Generating bundle for " + n);
 		// Ack all batches received from the neighbour
-		neighbourLock.writeLock().lock();
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return;
+			messageStatusLock.writeLock().lock();
 			try {
 				Txn txn = db.startTransaction();
 				try {
@@ -269,9 +321,15 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			} finally {
-			neighbourLock.writeLock().unlock();
+				messageStatusLock.writeLock().unlock();
+			}
+		} finally {
+			contactLock.readLock().unlock();
 		}
 		// Add a list of subscriptions
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return;
 			subscriptionLock.readLock().lock();
 			try {
 				Txn txn = db.startTransaction();
@@ -291,6 +349,9 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 			} finally {
 				subscriptionLock.readLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 		// Add as many messages as possible to the bundle
 		long capacity = b.getCapacity();
 		while(true) {
@@ -309,11 +370,14 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	private Batch fillBatch(NeighbourId n, long capacity) throws DbException {
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return null;
 			messageLock.readLock().lock();
 			try {
 				Set<MessageId> sent;
 				Batch b;
-			neighbourLock.readLock().lock();
+				messageStatusLock.readLock().lock();
 				try {
 					Txn txn = db.startTransaction();
 					try {
@@ -338,10 +402,10 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						throw e;
 					}
 				} finally {
-				neighbourLock.readLock().unlock();
+					messageStatusLock.readLock().unlock();
 				}
 				// Record the contents of the batch
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					Txn txn = db.startTransaction();
 					try {
@@ -354,11 +418,14 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						throw e;
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.readLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 	}
 
 	public void receiveBundle(NeighbourId n, Bundle b) throws DbException {
@@ -366,9 +433,12 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 			LOG.fine("Received bundle from " + n + ", "
 					+ b.getSize() + " bytes");
 		// Mark all messages in acked batches as seen
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return;
 			messageLock.readLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					int acks = 0;
 					for(BatchId ack : b.getAcks()) {
@@ -385,13 +455,19 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					if(LOG.isLoggable(Level.FINE))
 						LOG.fine("Received " + acks + " acks");
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.readLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 		// Update the neighbour's subscriptions
-		neighbourLock.writeLock().lock();
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return;
+			messageStatusLock.writeLock().lock();
 			try {
 				Txn txn = db.startTransaction();
 				try {
@@ -409,16 +485,22 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			} finally {
-			neighbourLock.writeLock().unlock();
+				messageStatusLock.writeLock().unlock();
+			}
+		} finally {
+			contactLock.readLock().lock();
 		}
 		// Store the messages
 		int batches = 0;
 		for(Batch batch : b.getBatches()) {
 			batches++;
 			waitForPermissionToWrite();
+			contactLock.readLock().lock();
+			try {
+				if(!containsNeighbour(n)) return;
 				messageLock.writeLock().lock();
 				try {
-				neighbourLock.writeLock().lock();
+					messageStatusLock.writeLock().lock();
 					try {
 						subscriptionLock.readLock().lock();
 						try {
@@ -427,7 +509,8 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 								int received = 0, stored = 0;
 								for(Message m : batch.getMessages()) {
 									received++;
-								if(db.containsSubscription(txn, m.getGroup())) {
+									GroupId g = m.getGroup();
+									if(db.containsSubscription(txn, g)) {
 										if(storeMessage(txn, m, n)) stored++;
 									}
 								}
@@ -444,19 +527,25 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 							subscriptionLock.readLock().unlock();
 						}
 					} finally {
-					neighbourLock.writeLock().unlock();
+						messageStatusLock.writeLock().unlock();
 					}
 				} finally {
 					messageLock.writeLock().unlock();
 				}
+			} finally {
+				contactLock.readLock().unlock();
+			}
 		}
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine("Received " + batches + " batches");
 		// Find any lost batches that need to be retransmitted
 		Set<BatchId> lost;
+		contactLock.readLock().lock();
+		try {
+			if(!containsNeighbour(n)) return;
 			messageLock.readLock().lock();
 			try {
-			neighbourLock.writeLock().lock();
+				messageStatusLock.writeLock().lock();
 				try {
 					Txn txn = db.startTransaction();
 					try {
@@ -467,15 +556,21 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						throw e;
 					}
 				} finally {
-				neighbourLock.writeLock().unlock();
+					messageStatusLock.writeLock().unlock();
 				}
 			} finally {
 				messageLock.readLock().unlock();
 			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
 		for(BatchId batch : lost) {
+			contactLock.readLock().lock();
+			try {
+				if(!containsNeighbour(n)) return;
 				messageLock.readLock().lock();
 				try {
-				neighbourLock.writeLock().lock();
+					messageStatusLock.writeLock().lock();
 					try {
 						Txn txn = db.startTransaction();
 						try {
@@ -488,11 +583,14 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 							throw e;
 						}
 					} finally {
-					neighbourLock.writeLock().unlock();
+						messageStatusLock.writeLock().unlock();
 					}
 				} finally {
 					messageLock.readLock().unlock();
 				}
+			} finally {
+				contactLock.readLock().unlock();
+			}
 		}
 		System.gc();
 	}

components/net/sf/briar/db/SynchronizedDatabaseComponent.java

@@ -30,8 +30,9 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	 * interface to find out which calls require which locks.
 	 */
 
+	private final Object contactLock = new Object();
 	private final Object messageLock = new Object();
-	private final Object neighbourLock = new Object();
+	private final Object messageStatusLock = new Object();
 	private final Object ratingLock = new Object();
 	private final Object subscriptionLock = new Object();
 
@@ -42,8 +43,9 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	protected void expireMessages(long size) throws DbException {
+		synchronized(contactLock) {
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					Txn txn = db.startTransaction();
 					try {
 						for(MessageId m : db.getOldMessages(txn, size)) {
@@ -57,10 +59,12 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
 
 	public void close() throws DbException {
+		synchronized(contactLock) {
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					synchronized(ratingLock) {
 						synchronized(subscriptionLock) {
 							db.close();
@@ -69,10 +73,12 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
 
 	public void addNeighbour(NeighbourId n) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Adding neighbour " + n);
-		synchronized(neighbourLock) {
+		synchronized(contactLock) {
+			synchronized(messageStatusLock) {
 				Txn txn = db.startTransaction();
 				try {
 					db.addNeighbour(txn, n);
@@ -83,11 +89,13 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
 
 	public void addLocallyGeneratedMessage(Message m) throws DbException {
 		waitForPermissionToWrite();
+		synchronized(contactLock) {
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					synchronized(subscriptionLock) {
 						Txn txn = db.startTransaction();
 						try {
@@ -107,6 +115,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
 
 	public Rating getRating(AuthorId a) throws DbException {
 		synchronized(ratingLock) {
@@ -173,8 +182,9 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 
 	public void unsubscribe(GroupId g) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Unsubscribing from " + g);
+		synchronized(contactLock) {
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					synchronized(subscriptionLock) {
 						Txn txn = db.startTransaction();
 						try {
@@ -188,11 +198,14 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
 
 	public void generateBundle(NeighbourId n, Bundle b) throws DbException {
 		if(LOG.isLoggable(Level.FINE)) LOG.fine("Generating bundle for " + n);
 		// Ack all batches received from the neighbour
-		synchronized(neighbourLock) {
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return;
+			synchronized(messageStatusLock) {
 				Txn txn = db.startTransaction();
 				try {
 					int numAcks = 0;
@@ -208,7 +221,10 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			}
+		}
 		// Add a list of subscriptions
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return;
 			synchronized(subscriptionLock) {
 				Txn txn = db.startTransaction();
 				try {
@@ -225,6 +241,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			}
+		}
 		// Add as many messages as possible to the bundle
 		long capacity = b.getCapacity();
 		while(true) {
@@ -243,8 +260,10 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	private Batch fillBatch(NeighbourId n, long capacity) throws DbException {
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return null;
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					Txn txn = db.startTransaction();
 					try {
 						capacity = Math.min(capacity, Batch.CAPACITY);
@@ -274,14 +293,33 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+	}
+
+	public void removeNeighbour(NeighbourId n) throws DbException {
+		if(LOG.isLoggable(Level.FINE)) LOG.fine("Removing neighbour " + n);
+		synchronized(contactLock) {
+			synchronized(messageStatusLock) {
+				Txn txn = db.startTransaction();
+				try {
+					db.removeNeighbour(txn, n);
+					db.commitTransaction(txn);
+				} catch(DbException e) {
+					db.abortTransaction(txn);
+					throw e;
+				}
+			}
+		}
+	}
 
 	public void receiveBundle(NeighbourId n, Bundle b) throws DbException {
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine("Received bundle from " + n + ", "
 					+ b.getSize() + " bytes");
 		// Mark all messages in acked batches as seen
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return;
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					int acks = 0;
 					for(BatchId ack : b.getAcks()) {
 						acks++;
@@ -298,8 +336,11 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 						LOG.fine("Received " + acks + " acks");
 				}
 			}
+		}
 		// Update the neighbour's subscriptions
-		synchronized(neighbourLock) {
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return;
+			synchronized(messageStatusLock) {
 				Txn txn = db.startTransaction();
 				try {
 					db.clearSubscriptions(txn, n);
@@ -316,20 +357,24 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					throw e;
 				}
 			}
+		}
 		// Store the messages
 		int batches = 0;
 		for(Batch batch : b.getBatches()) {
 			batches++;
 			waitForPermissionToWrite();
+			synchronized(contactLock) {
+				if(!containsNeighbour(n)) return;
 				synchronized(messageLock) {
-				synchronized(neighbourLock) {
+					synchronized(messageStatusLock) {
 						synchronized(subscriptionLock) {
 							Txn txn = db.startTransaction();
 							try {
 								int received = 0, stored = 0;
 								for(Message m : batch.getMessages()) {
 									received++;
-								if(db.containsSubscription(txn, m.getGroup())) {
+									GroupId g = m.getGroup();
+									if(db.containsSubscription(txn, g)) {
 										if(storeMessage(txn, m, n)) stored++;
 									}
 								}
@@ -346,12 +391,15 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					}
 				}
 			}
+		}
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine("Received " + batches + " batches");
 		// Find any lost batches that need to be retransmitted
 		Set<BatchId> lost;
+		synchronized(contactLock) {
+			if(!containsNeighbour(n)) return;
 			synchronized(messageLock) {
-			synchronized(neighbourLock) {
+				synchronized(messageStatusLock) {
 					Txn txn = db.startTransaction();
 					try {
 						lost = db.addReceivedBundle(txn, n, b.getId());
@@ -362,9 +410,12 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					}
 				}
 			}
+		}
 		for(BatchId batch : lost) {
+			synchronized(contactLock) {
+				if(!containsNeighbour(n)) return;
 				synchronized(messageLock) {
-				synchronized(neighbourLock) {
+					synchronized(messageStatusLock) {
 						Txn txn = db.startTransaction();
 						try {
 							if(LOG.isLoggable(Level.FINE))
@@ -378,6 +429,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 					}
 				}
 			}
+		}
 		System.gc();
 	}
 }