Added support for registering listeners with the database that are

called when new messages are available, and a new method
hasSendableMessages(ContactId) that listeners can call to see whether
it's worth trying to create a batch.

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

@@ -109,28 +109,28 @@ interface Database<T> {
 	void addSubscription(T txn, Group g) throws DbException;
 
 	/**
-	 * Returns true iff the database contains the given contact.
+	 * Returns true if the database contains the given contact.
 	 * <p>
 	 * Locking: contacts read.
 	 */
 	boolean containsContact(T txn, ContactId c) throws DbException;
 
 	/**
-	 * Returns true iff the database contains the given message.
+	 * Returns true if the database contains the given message.
 	 * <p>
 	 * Locking: messages read.
 	 */
 	boolean containsMessage(T txn, MessageId m) throws DbException;
 
 	/**
-	 * Returns true iff the user is subscribed to the given group.
+	 * Returns true if the user is subscribed to the given group.
 	 * <p>
 	 * Locking: subscriptions read.
 	 */
 	boolean containsSubscription(T txn, GroupId g) throws DbException;
 
 	/**
-	 * Returns true iff the user is subscribed to the given group and the
+	 * Returns true if the user is subscribed to the given group and the
 	 * group is visible to the given contact.
 	 * <p>
 	 * Locking: contacts read, subscriptions read.
@@ -189,7 +189,8 @@ interface Database<T> {
 	 * if the message is not present in the database or is not sendable to the
 	 * given contact.
 	 * <p>
-	 * Locking: contacts read, messages read, messageStatuses read.
+	 * Locking: contacts read, messages read, messageStatuses read,
+	 * subscriptions read.
 	 */
 	byte[] getMessageIfSendable(T txn, ContactId c, MessageId m)
 	throws DbException;
@@ -246,7 +247,8 @@ interface Database<T> {
 	 * Returns the IDs of some messages that are eligible to be sent to the
 	 * given contact, with a total size less than or equal to the given size.
 	 * <p>
-	 * Locking: contacts read, messages read, messageStatuses read.
+	 * Locking: contacts read, messages read, messageStatuses read,
+	 * subscriptions read.
 	 */
 	Collection<MessageId> getSendableMessages(T txn, ContactId c, int size)
 	throws DbException;
@@ -293,6 +295,13 @@ interface Database<T> {
 	Collection<Group> getVisibleSubscriptions(T txn, ContactId c)
 	throws DbException;
 
+	/**
+	 * Returns true if any messages are sendable to the given contact.
+	 * <p>
+	 * Locking: contacts read, messages read, messageStatuses read.
+	 */
+	boolean hasSendableMessages(T txn, ContactId c) throws DbException;
+
 	/**
 	 * Removes an outstanding batch that has been acknowledged. Any messages in
 	 * the batch that are still considered outstanding (Status.SENT) with

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

@@ -25,7 +25,7 @@ interface DatabaseCleaner {
 		void checkFreeSpaceAndClean() throws DbException;
 
 		/**
-		 * Returns true iff the amount of free storage space available to the
+		 * Returns true if the amount of free storage space available to the
 		 * database should be checked.
 		 */
 		boolean shouldCheckFreeSpace();

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

@@ -1,5 +1,8 @@
 package net.sf.briar.db;
 
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -7,6 +10,7 @@ import net.sf.briar.api.ContactId;
 import net.sf.briar.api.Rating;
 import net.sf.briar.api.db.DatabaseComponent;
 import net.sf.briar.api.db.DbException;
+import net.sf.briar.api.db.MessageListener;
 import net.sf.briar.api.db.Status;
 import net.sf.briar.api.protocol.AuthorId;
 import net.sf.briar.api.protocol.Message;
@@ -25,6 +29,8 @@ DatabaseCleaner.Callback {
 	protected final Database<Txn> db;
 	protected final DatabaseCleaner cleaner;
 
+	private final List<MessageListener> listeners =
+		new ArrayList<MessageListener>(); // Locking: self
 	private final Object spaceLock = new Object();
 	private final Object writeLock = new Object();
 	private long bytesStoredSinceLastCheck = 0L; // Locking: spaceLock
@@ -41,6 +47,18 @@ DatabaseCleaner.Callback {
 		cleaner.startCleaning();
 	}
 
+	public void addListener(MessageListener m) {
+		synchronized(listeners) {
+			listeners.add(m);
+		}
+	}
+
+	public void removeListener(MessageListener m) {
+		synchronized(listeners) {
+			listeners.remove(m);
+		}
+	}
+
 	/**
 	 * Removes the oldest messages from the database, with a total size less
 	 * than or equal to the given size.
@@ -61,6 +79,18 @@ DatabaseCleaner.Callback {
 		return sendability;
 	}
 
+	/** Notifies all MessageListeners that new messages may be available. */
+	protected void callMessageListeners() {
+		synchronized(listeners) {
+			if(!listeners.isEmpty()) {
+				// Shuffle the listeners so we don't always send new messages
+				// to contacts in the same order
+				Collections.shuffle(listeners);
+				for(MessageListener m : listeners) m.messagesAdded();
+			}
+		}
+	}
+
 	public void checkFreeSpaceAndClean() throws DbException {
 		long freeSpace = db.getFreeSpace();
 		while(freeSpace < MIN_FREE_SPACE) {
@@ -85,7 +115,7 @@ DatabaseCleaner.Callback {
 	}
 
 	/**
-	 * Returns true iff the database contains the given contact.
+	 * Returns true if the database contains the given contact.
 	 * <p>
 	 * Locking: contacts read.
 	 */
@@ -121,7 +151,7 @@ DatabaseCleaner.Callback {
 			if(bytesStoredSinceLastCheck > MAX_BYTES_BETWEEN_SPACE_CHECKS) {
 				if(LOG.isLoggable(Level.FINE))
 					LOG.fine(bytesStoredSinceLastCheck
-						+ " bytes stored since last check");
+							+ " bytes stored since last check");
 				bytesStoredSinceLastCheck = 0L;
 				timeOfLastCheck = now;
 				return true;
@@ -234,7 +264,7 @@ DatabaseCleaner.Callback {
 		}
 		if(LOG.isLoggable(Level.FINE))
 			LOG.fine(direct + " messages affected directly, "
-				+ indirect + " indirectly");
+					+ indirect + " indirectly");
 	}
 
 	/**

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

@@ -1226,6 +1226,42 @@ abstract class JdbcDatabase implements Database<Connection> {
 		}
 	}
 
+	public boolean hasSendableMessages(Connection txn, ContactId c)
+	throws DbException {
+		PreparedStatement ps = null;
+		ResultSet rs = null;
+		try {
+			String sql = "SELECT messages.messageId FROM messages"
+				+ " JOIN contactSubscriptions"
+				+ " ON messages.groupId = contactSubscriptions.groupId"
+				+ " JOIN visibilities"
+				+ " ON messages.groupId = visibilities.groupId"
+				+ " JOIN statuses ON messages.messageId = statuses.messageId"
+				+ " WHERE contactSubscriptions.contactId = ?"
+				+ " AND visibilities.contactId = ?"
+				+ " AND statuses.contactId = ?"
+				+ " AND status = ? AND sendability > ZERO()"
+				+ " LIMIT ?";
+			ps = txn.prepareStatement(sql);
+			ps.setInt(1, c.getInt());
+			ps.setInt(2, c.getInt());
+			ps.setInt(3, c.getInt());
+			ps.setShort(4, (short) Status.NEW.ordinal());
+			ps.setInt(5, 1);
+			rs = ps.executeQuery();
+			boolean found = rs.next();
+			assert !rs.next();
+			rs.close();
+			ps.close();
+			return found;
+		} catch(SQLException e) {
+			tryToClose(rs);
+			tryToClose(ps);
+			tryToClose(txn);
+			throw new DbException(e);
+		}
+	}
+
 	public void removeAckedBatch(Connection txn, ContactId c, BatchId b)
 	throws DbException {
 		PreparedStatement ps = null;

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

@@ -151,6 +151,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	public void addLocallyGeneratedMessage(Message m) throws DbException {
+		boolean added = false;
 		waitForPermissionToWrite();
 		contactLock.readLock().lock();
 		try {
@@ -165,7 +166,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 							// Don't store the message if the user has
 							// unsubscribed from the group
 							if(db.containsSubscription(txn, m.getGroup())) {
-								boolean added = storeMessage(txn, m, null);
+								added = storeMessage(txn, m, null);
 								if(!added) {
 									if(LOG.isLoggable(Level.FINE))
 										LOG.fine("Duplicate local message");
@@ -191,6 +192,8 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		} finally {
 			contactLock.readLock().unlock();
 		}
+		// Call the listeners outside the lock
+		if(added) callMessageListeners();
 	}
 
 	public void findLostBatches(ContactId c) throws DbException {
@@ -293,26 +296,32 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				int bytesSent = 0;
 				messageStatusLock.readLock().lock();
 				try {
-					Txn txn = db.startTransaction();
+					subscriptionLock.readLock().lock();
 					try {
-						int capacity = b.getCapacity();
-						Iterator<MessageId> it =
-							db.getSendableMessages(txn, c, capacity).iterator();
-						sent = new ArrayList<MessageId>();
-						while(it.hasNext()) {
-							MessageId m = it.next();
-							byte[] message = db.getMessage(txn, m);
-							if(!b.writeMessage(message)) break;
-							bytesSent += message.length;
-							sent.add(m);
+						Txn txn = db.startTransaction();
+						try {
+							int capacity = b.getCapacity();
+							Collection<MessageId> sendable =
+								db.getSendableMessages(txn, c, capacity);
+							Iterator<MessageId> it = sendable.iterator();
+							sent = new ArrayList<MessageId>();
+							while(it.hasNext()) {
+								MessageId m = it.next();
+								byte[] raw = db.getMessage(txn, m);
+								if(!b.writeMessage(raw)) break;
+								bytesSent += raw.length;
+								sent.add(m);
+							}
+							db.commitTransaction(txn);
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						} catch(IOException e) {
+							db.abortTransaction(txn);
+							throw e;
 						}
-						db.commitTransaction(txn);
-					} catch(DbException e) {
-						db.abortTransaction(txn);
-						throw e;
-					} catch(IOException e) {
-						db.abortTransaction(txn);
-						throw e;
+					} finally {
+						subscriptionLock.readLock().unlock();
 					}
 				} finally {
 					messageStatusLock.readLock().unlock();
@@ -351,24 +360,29 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				Collection<MessageId> sent;
 				messageStatusLock.readLock().lock();
 				try{
-					Txn txn = db.startTransaction();
+					subscriptionLock.readLock().lock();
 					try {
-						sent = new ArrayList<MessageId>();
-						int bytesSent = 0;
-						for(MessageId m : requested) {
-							byte[] message = db.getMessageIfSendable(txn, c, m);
-							if(message == null) continue;
-							if(!b.writeMessage(message)) break;
-							bytesSent += message.length;
-							sent.add(m);
+						Txn txn = db.startTransaction();
+						try {
+							sent = new ArrayList<MessageId>();
+							int bytesSent = 0;
+							for(MessageId m : requested) {
+								byte[] raw = db.getMessageIfSendable(txn, c, m);
+								if(raw == null) continue;
+								if(!b.writeMessage(raw)) break;
+								bytesSent += raw.length;
+								sent.add(m);
+							}
+							db.commitTransaction(txn);
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						} catch(IOException e) {
+							db.abortTransaction(txn);
+							throw e;
 						}
-						db.commitTransaction(txn);
-					} catch(DbException e) {
-						db.abortTransaction(txn);
-						throw e;
-					} catch(IOException e) {
-						db.abortTransaction(txn);
-						throw e;
+					} finally {
+						subscriptionLock.readLock().unlock();
 					}
 				} finally {
 					messageStatusLock.readLock().unlock();
@@ -610,6 +624,39 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		}
 	}
 
+	public boolean hasSendableMessages(ContactId c) throws DbException {
+		contactLock.readLock().lock();
+		try {
+			if(!containsContact(c)) throw new NoSuchContactException();
+			messageLock.readLock().lock();
+			try {
+				messageStatusLock.readLock().lock();
+				try {
+					subscriptionLock.readLock().lock();
+					try {
+						Txn txn = db.startTransaction();
+						try {
+							boolean has = db.hasSendableMessages(txn, c);
+							db.commitTransaction(txn);
+							return has;
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						}
+					} finally {
+						subscriptionLock.readLock().unlock();
+					}
+				} finally {
+					messageStatusLock.readLock().unlock();
+				}
+			} finally {
+				messageLock.readLock().unlock();
+			}
+		} finally {
+			contactLock.readLock().unlock();
+		}
+	}
+
 	public void receiveAck(ContactId c, Ack a) throws DbException {
 		// Mark all messages in acked batches as seen
 		contactLock.readLock().lock();
@@ -644,6 +691,7 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	public void receiveBatch(ContactId c, Batch b) throws DbException {
+		boolean anyAdded = false;
 		waitForPermissionToWrite();
 		contactLock.readLock().lock();
 		try {
@@ -661,7 +709,10 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 								received++;
 								GroupId g = m.getGroup();
 								if(db.containsVisibleSubscription(txn, g, c)) {
-									if(storeMessage(txn, m, c)) stored++;
+									if(storeMessage(txn, m, c)) {
+										anyAdded = true;
+										stored++;
+									}
 								}
 							}
 							if(LOG.isLoggable(Level.FINE))
@@ -685,6 +736,8 @@ class ReadWriteLockDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		} finally {
 			contactLock.readLock().unlock();
 		}
+		// Call the listeners outside the lock
+		if(anyAdded) callMessageListeners();
 	}
 
 	public void receiveOffer(ContactId c, Offer o, RequestWriter r)

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

@@ -116,6 +116,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	public void addLocallyGeneratedMessage(Message m) throws DbException {
+		boolean added = false;
 		waitForPermissionToWrite();
 		synchronized(contactLock) {
 			synchronized(messageLock) {
@@ -126,7 +127,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 							// Don't store the message if the user has
 							// unsubscribed from the group
 							if(db.containsSubscription(txn, m.getGroup())) {
-								boolean added = storeMessage(txn, m, null);
+								added = storeMessage(txn, m, null);
 								if(!added) {
 									if(LOG.isLoggable(Level.FINE))
 										LOG.fine("Duplicate local message");
@@ -144,6 +145,8 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+		// Call the listeners outside the lock
+		if(added) callMessageListeners();
 	}
 
 	public void findLostBatches(ContactId c) throws DbException {
@@ -217,31 +220,34 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 			if(!containsContact(c)) throw new NoSuchContactException();
 			synchronized(messageLock) {
 				synchronized(messageStatusLock) {
-					Txn txn = db.startTransaction();
-					try {
-						int capacity = b.getCapacity();
-						Iterator<MessageId> it =
-							db.getSendableMessages(txn, c, capacity).iterator();
-						Collection<MessageId> sent = new ArrayList<MessageId>();
-						int bytesSent = 0;
-						while(it.hasNext()) {
-							MessageId m = it.next();
-							byte[] message = db.getMessage(txn, m);
-							if(!b.writeMessage(message)) break;
-							bytesSent += message.length;
-							sent.add(m);
+					synchronized(subscriptionLock) {
+						Txn txn = db.startTransaction();
+						try {
+							int capacity = b.getCapacity();
+							Collection<MessageId> sendable =
+								db.getSendableMessages(txn, c, capacity);
+							Iterator<MessageId> it = sendable.iterator();
+							Collection<MessageId> sent =
+								new ArrayList<MessageId>();
+							int bytesSent = 0;
+							while(it.hasNext()) {
+								MessageId m = it.next();
+								byte[] raw = db.getMessage(txn, m);
+								if(!b.writeMessage(raw)) break;
+								bytesSent += raw.length;
+								sent.add(m);
+							}
+							BatchId id = b.finish();
+							if(!sent.isEmpty())
+								db.addOutstandingBatch(txn, c, id, sent);
+							db.commitTransaction(txn);
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						} catch(IOException e) {
+							db.abortTransaction(txn);
+							throw e;
 						}
-						BatchId id = b.finish();
-						// Record the contents of the batch, unless it's empty
-						if(!sent.isEmpty())
-							db.addOutstandingBatch(txn, c, id, sent);
-						db.commitTransaction(txn);
-					} catch(DbException e) {
-						db.abortTransaction(txn);
-						throw e;
-					} catch(IOException e) {
-						db.abortTransaction(txn);
-						throw e;
 					}
 				}
 			}
@@ -254,29 +260,31 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 			if(!containsContact(c)) throw new NoSuchContactException();
 			synchronized(messageLock) {
 				synchronized(messageStatusLock) {
-					Txn txn = db.startTransaction();
-					try {
-						Collection<MessageId> sent = new ArrayList<MessageId>();
-						int bytesSent = 0;
-						for(MessageId m : requested) {
-							byte[] message = db.getMessageIfSendable(txn, c, m);
-							if(message == null) continue;
-							if(!b.writeMessage(message)) break;
-							bytesSent += message.length;
-							sent.add(m);
+					synchronized(subscriptionLock) {
+						Txn txn = db.startTransaction();
+						try {
+							Collection<MessageId> sent =
+								new ArrayList<MessageId>();
+							int bytesSent = 0;
+							for(MessageId m : requested) {
+								byte[] raw = db.getMessageIfSendable(txn, c, m);
+								if(raw == null) continue;
+								if(!b.writeMessage(raw)) break;
+								bytesSent += raw.length;
+								sent.add(m);
+							}
+							BatchId id = b.finish();
+							if(!sent.isEmpty())
+								db.addOutstandingBatch(txn, c, id, sent);
+							db.commitTransaction(txn);
+							return sent;
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						} catch(IOException e) {
+							db.abortTransaction(txn);
+							throw e;
 						}
-						BatchId id = b.finish();
-						// Record the contents of the batch, unless it's empty
-						if(!sent.isEmpty())
-							db.addOutstandingBatch(txn, c, id, sent);
-						db.commitTransaction(txn);
-						return sent;
-					} catch(DbException e) {
-						db.abortTransaction(txn);
-						throw e;
-					} catch(IOException e) {
-						db.abortTransaction(txn);
-						throw e;
 					}
 				}
 			}
@@ -450,6 +458,27 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 		}
 	}
 
+	public boolean hasSendableMessages(ContactId c) throws DbException {
+		synchronized(contactLock) {
+			if(!containsContact(c)) throw new NoSuchContactException();
+			synchronized(messageLock) {
+				synchronized(messageStatusLock) {
+					synchronized(subscriptionLock) {
+						Txn txn = db.startTransaction();
+						try {
+							boolean has = db.hasSendableMessages(txn, c);
+							db.commitTransaction(txn);
+							return has;
+						} catch(DbException e) {
+							db.abortTransaction(txn);
+							throw e;
+						}
+					}
+				}
+			}
+		}
+	}
+
 	public void receiveAck(ContactId c, Ack a) throws DbException {
 		// Mark all messages in acked batches as seen
 		synchronized(contactLock) {
@@ -475,6 +504,7 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 	}
 
 	public void receiveBatch(ContactId c, Batch b) throws DbException {
+		boolean anyAdded = false;
 		waitForPermissionToWrite();
 		synchronized(contactLock) {
 			if(!containsContact(c)) throw new NoSuchContactException();
@@ -488,7 +518,10 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 								received++;
 								GroupId g = m.getGroup();
 								if(db.containsVisibleSubscription(txn, g, c)) {
-									if(storeMessage(txn, m, c)) stored++;
+									if(storeMessage(txn, m, c)) {
+										anyAdded = true;
+										stored++;
+									}
 								}
 							}
 							if(LOG.isLoggable(Level.FINE))
@@ -504,6 +537,8 @@ class SynchronizedDatabaseComponent<Txn> extends DatabaseComponentImpl<Txn> {
 				}
 			}
 		}
+		// Call the listeners outside the lock
+		if(anyAdded) callMessageListeners();
 	}
 
 	public void receiveOffer(ContactId c, Offer o, RequestWriter r)