Poll for connections in series, with a delay between attempts.

The delay reduces interference between Bluetooth and wifi.

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPlugin.java

@@ -31,6 +31,7 @@ import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Executor;
 import java.util.concurrent.LinkedBlockingQueue;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
@@ -78,11 +79,12 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	AndroidBluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			SecureRandom secureRandom, AndroidExecutor androidExecutor,
-			Context appContext, Clock clock, Backoff backoff,
-			PluginCallback callback, int maxLatency, int maxIdleTime) {
-		super(connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
-				backoff, callback, maxLatency, maxIdleTime);
+			ScheduledExecutorService scheduler, SecureRandom secureRandom,
+			AndroidExecutor androidExecutor, Context appContext, Clock clock,
+			Backoff backoff, PluginCallback callback, int maxLatency,
+			int maxIdleTime) {
+		super(connectionLimiter, timeoutMonitor, ioExecutor, scheduler,
+				secureRandom, backoff, callback, maxLatency, maxIdleTime);
 		this.androidExecutor = androidExecutor;
 		this.appContext = appContext;
 		this.clock = clock;

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothPluginFactory.java

@@ -16,6 +16,7 @@ import org.briarproject.bramble.api.system.Clock;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -32,6 +33,7 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
+	private final ScheduledExecutorService scheduler;
 	private final AndroidExecutor androidExecutor;
 	private final Context appContext;
 	private final SecureRandom secureRandom;
@@ -41,10 +43,12 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private final BackoffFactory backoffFactory;
 
 	public AndroidBluetoothPluginFactory(Executor ioExecutor,
-			AndroidExecutor androidExecutor, Context appContext,
-			SecureRandom secureRandom, EventBus eventBus, Clock clock,
-			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
+			ScheduledExecutorService scheduler, AndroidExecutor androidExecutor,
+			Context appContext, SecureRandom secureRandom, EventBus eventBus,
+			Clock clock, TimeoutMonitor timeoutMonitor,
+			BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
+		this.scheduler = scheduler;
 		this.androidExecutor = androidExecutor;
 		this.appContext = appContext;
 		this.secureRandom = secureRandom;
@@ -67,12 +71,12 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl(eventBus, clock);
+				new BluetoothConnectionLimiterImpl();
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		AndroidBluetoothPlugin plugin = new AndroidBluetoothPlugin(
-				connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
-				androidExecutor, appContext, clock, backoff,
+				connectionLimiter, timeoutMonitor, ioExecutor, scheduler,
+				secureRandom, androidExecutor, appContext, clock, backoff,
 				callback, MAX_LATENCY, MAX_IDLE_TIME);
 		eventBus.addListener(plugin);
 		return plugin;

bramble-android/src/main/java/org/briarproject/bramble/plugin/bluetooth/AndroidBluetoothTransportConnection.java

@@ -50,7 +50,7 @@ class AndroidBluetoothTransportConnection
 		try {
 			socket.close();
 		} finally {
-			connectionLimiter.connectionClosed(this, exception);
+			connectionLimiter.connectionClosed(this);
 		}
 	}
 }

bramble-api/src/main/java/org/briarproject/bramble/api/sync/SyncSessionFactory.java

@@ -2,7 +2,6 @@ package org.briarproject.bramble.api.sync;
 
 import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.InputStream;
@@ -12,9 +11,9 @@ public interface SyncSessionFactory {
 
 	SyncSession createIncomingSession(ContactId c, InputStream in);
 
-	SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
-			int maxLatency, StreamWriter streamWriter);
+	SyncSession createSimplexOutgoingSession(ContactId c, int maxLatency,
+			StreamWriter streamWriter);
 
-	SyncSession createDuplexOutgoingSession(ContactId c, TransportId t,
-			int maxLatency, int maxIdleTime, StreamWriter streamWriter);
+	SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
+			int maxIdleTime, StreamWriter streamWriter);
 }

bramble-api/src/main/java/org/briarproject/bramble/api/sync/event/CloseSyncConnectionsEvent.java

@@ -1,26 +0,0 @@
-package org.briarproject.bramble.api.sync.event;
-
-import org.briarproject.bramble.api.event.Event;
-import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportId;
-
-import javax.annotation.concurrent.Immutable;
-
-/**
- * An event that is broadcast when all sync connections using a given
- * transport should be closed.
- */
-@Immutable
-@NotNullByDefault
-public class CloseSyncConnectionsEvent extends Event {
-
-	private final TransportId transportId;
-
-	public CloseSyncConnectionsEvent(TransportId transportId) {
-		this.transportId = transportId;
-	}
-
-	public TransportId getTransportId() {
-		return transportId;
-	}
-}

bramble-api/src/main/java/org/briarproject/bramble/api/system/Clock.java

@@ -11,6 +11,11 @@ public interface Clock {
 	 */
 	long currentTimeMillis();
 
+	/**
+	 * @see System#nanoTime()
+	 */
+	long nanoTime();
+
 	/**
 	 * @see Thread#sleep(long)
 	 */

bramble-api/src/test/java/org/briarproject/bramble/test/ArrayClock.java

@@ -16,6 +16,11 @@ public class ArrayClock implements Clock {
 		return times[index++];
 	}
 
+	@Override
+	public long nanoTime() {
+		return times[index++] * 1_000_000;
+	}
+
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

bramble-api/src/test/java/org/briarproject/bramble/test/SettableClock.java

@@ -17,6 +17,11 @@ public class SettableClock implements Clock {
 		return time.get();
 	}
 
+	@Override
+	public long nanoTime() {
+		return time.get() * 1_000_000;
+	}
+
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutInputStream.java

@@ -13,28 +13,28 @@ class TimeoutInputStream extends InputStream {
 
 	private final Clock clock;
 	private final InputStream in;
-	private final long timeoutMs;
+	private final long timeoutNs;
 	private final CloseListener listener;
 	private final Object lock = new Object();
 	@GuardedBy("lock")
-	private long readStartedMs = -1;
+	private long readStartedNs = -1;
 
-	TimeoutInputStream(Clock clock, InputStream in, long timeoutMs,
+	TimeoutInputStream(Clock clock, InputStream in, long timeoutNs,
 			CloseListener listener) {
 		this.clock = clock;
 		this.in = in;
-		this.timeoutMs = timeoutMs;
+		this.timeoutNs = timeoutNs;
 		this.listener = listener;
 	}
 
 	@Override
 	public int read() throws IOException {
 		synchronized (lock) {
-			readStartedMs = clock.currentTimeMillis();
+			readStartedNs = clock.nanoTime();
 		}
 		int input = in.read();
 		synchronized (lock) {
-			readStartedMs = -1;
+			readStartedNs = -1;
 		}
 		return input;
 	}
@@ -47,11 +47,11 @@ class TimeoutInputStream extends InputStream {
 	@Override
 	public int read(byte[] b, int off, int len) throws IOException {
 		synchronized (lock) {
-			readStartedMs = clock.currentTimeMillis();
+			readStartedNs = clock.nanoTime();
 		}
 		int read = in.read(b, off, len);
 		synchronized (lock) {
-			readStartedMs = -1;
+			readStartedNs = -1;
 		}
 		return read;
 	}
@@ -92,8 +92,8 @@ class TimeoutInputStream extends InputStream {
 
 	boolean hasTimedOut() {
 		synchronized (lock) {
-			return readStartedMs != -1 &&
-					clock.currentTimeMillis() - readStartedMs > timeoutMs;
+			return readStartedNs != -1 &&
+					clock.nanoTime() - readStartedNs > timeoutNs;
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/io/TimeoutMonitorImpl.java

@@ -52,7 +52,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 	public InputStream createTimeoutInputStream(InputStream in,
 			long timeoutMs) {
 		TimeoutInputStream stream = new TimeoutInputStream(clock, in,
-				timeoutMs, this::removeStream);
+				timeoutMs * 1_000_000, this::removeStream);
 		synchronized (lock) {
 			if (streams.isEmpty()) {
 				task = scheduler.scheduleWithFixedDelay(this::checkTimeouts,

bramble-core/src/main/java/org/briarproject/bramble/plugin/ConnectionManagerImpl.java

@@ -130,8 +130,8 @@ class ConnectionManagerImpl implements ConnectionManager {
 			TransportConnectionWriter w) throws IOException {
 		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
 				w.getOutputStream(), ctx);
-		return syncSessionFactory.createSimplexOutgoingSession(
-				requireNonNull(ctx.getContactId()), ctx.getTransportId(),
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createSimplexOutgoingSession(c,
 				w.getMaxLatency(), streamWriter);
 	}
 
@@ -139,8 +139,8 @@ class ConnectionManagerImpl implements ConnectionManager {
 			TransportConnectionWriter w) throws IOException {
 		StreamWriter streamWriter = streamWriterFactory.createStreamWriter(
 				w.getOutputStream(), ctx);
-		return syncSessionFactory.createDuplexOutgoingSession(
-				requireNonNull(ctx.getContactId()), ctx.getTransportId(),
+		ContactId c = requireNonNull(ctx.getContactId());
+		return syncSessionFactory.createDuplexOutgoingSession(c,
 				w.getMaxLatency(), w.getMaxIdleTime(), streamWriter);
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionLimiter.java

@@ -3,30 +3,9 @@ package org.briarproject.bramble.plugin.bluetooth;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 
-import static java.util.concurrent.TimeUnit.DAYS;
-import static java.util.concurrent.TimeUnit.MINUTES;
-import static java.util.concurrent.TimeUnit.SECONDS;
-
 @NotNullByDefault
 interface BluetoothConnectionLimiter {
 
-	/**
-	 * How long a connection must remain open before it's considered stable.
-	 */
-	long STABILITY_PERIOD_MS = SECONDS.toMillis(90);
-
-	/**
-	 * The minimum interval between attempts to raise the connection limit.
-	 * This is longer than {@link #STABILITY_PERIOD_MS} so we don't start
-	 * another attempt before knowing the outcome of the last one.
-	 */
-	long MIN_ATTEMPT_INTERVAL_MS = MINUTES.toMillis(2);
-
-	/**
-	 * The maximum interval between attempts to raise the connection limit.
-	 */
-	long MAX_ATTEMPT_INTERVAL_MS = DAYS.toMillis(2);
-
 	/**
 	 * Informs the limiter that key agreement has started.
 	 */
@@ -44,12 +23,12 @@ interface BluetoothConnectionLimiter {
 	boolean canOpenContactConnection();
 
 	/**
-	 * Informs the limiter that a contact connection has been opened.
+	 * Informs the limiter that a contact connection has been opened. The
+	 * limiter may close the new connection if key agreement is in progress.
 	 * <p/>
-	 * Returns true if the connection is allowed.
+	 * Returns false if the limiter has closed the new connection.
 	 */
-	boolean contactConnectionOpened(DuplexTransportConnection conn,
-			boolean incoming);
+	boolean contactConnectionOpened(DuplexTransportConnection conn);
 
 	/**
 	 * Informs the limiter that a key agreement connection has been opened.
@@ -58,13 +37,11 @@ interface BluetoothConnectionLimiter {
 
 	/**
 	 * Informs the limiter that the given connection has been closed.
-	 *
-	 * @param exception True if the connection was closed due to an exception.
 	 */
-	void connectionClosed(DuplexTransportConnection conn, boolean exception);
+	void connectionClosed(DuplexTransportConnection conn);
 
 	/**
-	 * Informs the limiter that the Bluetooth adapter has been disabled.
+	 * Informs the limiter that all connections have been closed.
 	 */
-	void bluetoothDisabled();
+	void allConnectionsClosed();
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionLimiterImpl.java

@@ -1,59 +1,46 @@
 package org.briarproject.bramble.plugin.bluetooth;
 
-import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
-import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
-import org.briarproject.bramble.api.system.Clock;
 
-import java.util.Iterator;
+import java.io.IOException;
+import java.util.ArrayList;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.logging.Logger;
 
-import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
-import javax.inject.Inject;
 
-import static java.lang.Math.min;
 import static java.util.logging.Level.INFO;
-import static java.util.logging.Logger.getLogger;
-import static org.briarproject.bramble.api.plugin.BluetoothConstants.ID;
+import static java.util.logging.Level.WARNING;
+import static org.briarproject.bramble.util.LogUtils.logException;
 
 @NotNullByDefault
 @ThreadSafe
 class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 
 	private static final Logger LOG =
-			getLogger(BluetoothConnectionLimiterImpl.class.getName());
-
-	private final EventBus eventBus;
-	private final Clock clock;
+			Logger.getLogger(BluetoothConnectionLimiterImpl.class.getName());
 
 	private final Object lock = new Object();
-	@GuardedBy("lock")
-	private final List<ConnectionRecord> connections = new LinkedList<>();
-	@GuardedBy("lock")
+	// The following are locking: lock
+	private final LinkedList<DuplexTransportConnection> connections =
+			new LinkedList<>();
 	private boolean keyAgreementInProgress = false;
-	@GuardedBy("lock")
-	private int connectionLimit = 1;
-	@GuardedBy("lock")
-	private long timeOfLastAttempt = 0,
-			attemptInterval = MIN_ATTEMPT_INTERVAL_MS;
-
-	@Inject
-	BluetoothConnectionLimiterImpl(EventBus eventBus, Clock clock) {
-		this.eventBus = eventBus;
-		this.clock = clock;
-	}
 
 	@Override
 	public void keyAgreementStarted() {
+		List<DuplexTransportConnection> close;
 		synchronized (lock) {
 			keyAgreementInProgress = true;
+			close = new ArrayList<>(connections);
+			connections.clear();
 		}
-		LOG.info("Key agreement started");
-		eventBus.broadcast(new CloseSyncConnectionsEvent(ID));
+		if (LOG.isLoggable(INFO)) {
+			LOG.info("Key agreement started, closing " + close.size() +
+					" connections");
+		}
+		for (DuplexTransportConnection conn : close) tryToClose(conn);
 	}
 
 	@Override
@@ -68,128 +55,62 @@ class BluetoothConnectionLimiterImpl implements BluetoothConnectionLimiter {
 	public boolean canOpenContactConnection() {
 		synchronized (lock) {
 			if (keyAgreementInProgress) {
-				LOG.info("Refusing contact connection during key agreement");
+				LOG.info("Can't open contact connection during key agreement");
 				return false;
 			} else {
-				long now = clock.currentTimeMillis();
-				return isContactConnectionAllowedByLimit(now);
+				LOG.info("Can open contact connection");
+				return true;
 			}
 		}
 	}
 
 	@Override
-	public boolean contactConnectionOpened(DuplexTransportConnection conn,
-			boolean incoming) {
+	public boolean contactConnectionOpened(DuplexTransportConnection conn) {
+		boolean accept = true;
 		synchronized (lock) {
 			if (keyAgreementInProgress) {
 				LOG.info("Refusing contact connection during key agreement");
-				return false;
+				accept = false;
 			} else {
-				long now = clock.currentTimeMillis();
-				if (incoming || isContactConnectionAllowedByLimit(now)) {
-					connections.add(new ConnectionRecord(conn, now));
-					if (!incoming && connections.size() > connectionLimit) {
-						LOG.info("Attempting to raise connection limit");
-						timeOfLastAttempt = now;
-					}
-					return true;
-				} else {
-					return false;
-				}
+				LOG.info("Accepting contact connection");
+				connections.add(conn);
 			}
 		}
+		if (!accept) tryToClose(conn);
+		return accept;
 	}
 
 	@Override
 	public void keyAgreementConnectionOpened(DuplexTransportConnection conn) {
 		synchronized (lock) {
 			LOG.info("Accepting key agreement connection");
-			connections.add(
-					new ConnectionRecord(conn, clock.currentTimeMillis()));
+			connections.add(conn);
+		}
+	}
+
+	private void tryToClose(DuplexTransportConnection conn) {
+		try {
+			conn.getWriter().dispose(false);
+			conn.getReader().dispose(false, false);
+		} catch (IOException e) {
+			logException(LOG, WARNING, e);
 		}
 	}
 
 	@Override
-	public void connectionClosed(DuplexTransportConnection conn,
-			boolean exception) {
+	public void connectionClosed(DuplexTransportConnection conn) {
 		synchronized (lock) {
-			Iterator<ConnectionRecord> it = connections.iterator();
-			while (it.hasNext()) {
-				if (it.next().connection == conn) {
-					long now = clock.currentTimeMillis();
-					if (exception) connectionFailed(now);
-					else considerRaisingConnectionLimit(now);
-					it.remove();
-					break;
-				}
-			}
+			connections.remove(conn);
 			if (LOG.isLoggable(INFO))
 				LOG.info("Connection closed, " + connections.size() + " open");
 		}
 	}
 
 	@Override
-	public void bluetoothDisabled() {
+	public void allConnectionsClosed() {
 		synchronized (lock) {
-			LOG.info("Bluetooth disabled");
-			considerRaisingConnectionLimit(clock.currentTimeMillis());
 			connections.clear();
-		}
-	}
-
-	@GuardedBy("lock")
-	private boolean isContactConnectionAllowedByLimit(long now) {
-		considerRaisingConnectionLimit(now);
-		if (connections.size() > connectionLimit) {
-			LOG.info("Refusing contact connection, above limit");
-			return false;
-		} else if (connections.size() < connectionLimit) {
-			LOG.info("Allowing contact connection, below limit");
-			return true;
-		} else if (now - timeOfLastAttempt >= attemptInterval) {
-			LOG.info("Allowing contact connection, at limit");
-			return true;
-		} else {
-			LOG.info("Refusing contact connection, at limit");
-			return false;
-		}
-	}
-
-	@GuardedBy("lock")
-	private void considerRaisingConnectionLimit(long now) {
-		int stable = 0;
-		for (ConnectionRecord rec : connections) {
-			if (now - rec.timeOpened >= STABILITY_PERIOD_MS) stable++;
-		}
-		if (stable > connectionLimit) {
-			LOG.info("Raising connection limit");
-			connectionLimit = stable;
-			attemptInterval = MIN_ATTEMPT_INTERVAL_MS;
-		}
-		if (LOG.isLoggable(INFO)) {
-			LOG.info(stable + " connections are stable, limit is "
-					+ connectionLimit);
-		}
-	}
-
-	@GuardedBy("lock")
-	private void connectionFailed(long now) {
-		if (connections.size() > connectionLimit &&
-				now - timeOfLastAttempt < STABILITY_PERIOD_MS) {
-			LOG.info("Connection failed above limit, increasing interval");
-			attemptInterval = min(attemptInterval * 2, MAX_ATTEMPT_INTERVAL_MS);
-		}
-	}
-
-	private static final class ConnectionRecord {
-
-		private final DuplexTransportConnection connection;
-		private final long timeOpened;
-
-		private ConnectionRecord(DuplexTransportConnection connection,
-				long timeOpened) {
-			this.connection = connection;
-			this.timeOpened = timeOpened;
+			LOG.info("All connections closed");
 		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/bluetooth/BluetoothPlugin.java

@@ -31,13 +31,17 @@ import org.briarproject.bramble.api.settings.event.SettingsUpdatedEvent;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.Collection;
+import java.util.LinkedList;
 import java.util.UUID;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
 
+import static java.util.concurrent.TimeUnit.MILLISECONDS;
+import static java.util.concurrent.TimeUnit.SECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Level.WARNING;
 import static java.util.logging.Logger.getLogger;
@@ -60,10 +64,18 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	private static final Logger LOG =
 			getLogger(BluetoothPlugin.class.getName());
 
+	/**
+	 * The delay between connection attempts when polling. This reduces
+	 * interference between Bluetooth and wifi.
+	 */
+	private static final long CONNECTION_ATTEMPT_INTERVAL_MS =
+			SECONDS.toMillis(5);
+
 	final BluetoothConnectionLimiter connectionLimiter;
 	final TimeoutMonitor timeoutMonitor;
 
 	private final Executor ioExecutor;
+	private final ScheduledExecutorService scheduler;
 	private final SecureRandom secureRandom;
 	private final Backoff backoff;
 	private final PluginCallback callback;
@@ -108,11 +120,13 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 
 	BluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			SecureRandom secureRandom, Backoff backoff,
-			PluginCallback callback, int maxLatency, int maxIdleTime) {
+			ScheduledExecutorService scheduler, SecureRandom secureRandom,
+			Backoff backoff, PluginCallback callback, int maxLatency,
+			int maxIdleTime) {
 		this.connectionLimiter = connectionLimiter;
 		this.timeoutMonitor = timeoutMonitor;
 		this.ioExecutor = ioExecutor;
+		this.scheduler = scheduler;
 		this.secureRandom = secureRandom;
 		this.backoff = backoff;
 		this.callback = callback;
@@ -130,7 +144,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	void onAdapterDisabled() {
 		LOG.info("Bluetooth disabled");
 		tryToClose(socket);
-		connectionLimiter.bluetoothDisabled();
+		connectionLimiter.allConnectionsClosed();
 		callback.transportDisabled();
 	}
 
@@ -232,25 +246,14 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 				return;
 			}
 			LOG.info("Connection received");
-			if (connectionLimiter.contactConnectionOpened(conn, true)) {
+			if (connectionLimiter.contactConnectionOpened(conn)) {
 				backoff.reset();
 				callback.handleConnection(conn);
-			} else {
-				tryToClose(conn);
 			}
 			if (!running) return;
 		}
 	}
 
-	private void tryToClose(DuplexTransportConnection conn) {
-		try {
-			conn.getWriter().dispose(false);
-			conn.getReader().dispose(false, false);
-		} catch (IOException e) {
-			logException(LOG, WARNING, e);
-		}
-	}
-
 	@Override
 	public void stop() {
 		running = false;
@@ -279,21 +282,31 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 			properties) {
 		if (!isRunning() || !shouldAllowContactConnections()) return;
 		backoff.increment();
-		for (Pair<TransportProperties, ConnectionHandler> p : properties) {
-			connect(p.getFirst(), p.getSecond());
+		LinkedList<Pair<TransportProperties, ConnectionHandler>> connectable =
+				new LinkedList<>();
+		for (Pair<TransportProperties, ConnectionHandler> pair : properties) {
+			TransportProperties p = pair.getFirst();
+			if (isNullOrEmpty(p.get(PROP_ADDRESS))) continue;
+			if (isNullOrEmpty(p.get(PROP_UUID))) continue;
+			connectable.add(pair);
 		}
+		if (!connectable.isEmpty()) poll(connectable);
 	}
 
-	private void connect(TransportProperties p, ConnectionHandler h) {
-		String address = p.get(PROP_ADDRESS);
-		if (isNullOrEmpty(address)) return;
-		String uuid = p.get(PROP_UUID);
-		if (isNullOrEmpty(uuid)) return;
+	private void poll(LinkedList<Pair<TransportProperties, ConnectionHandler>>
+			connectable) {
 		ioExecutor.execute(() -> {
-			DuplexTransportConnection d = createConnection(p);
+			if (!isRunning() || !shouldAllowContactConnections()) return;
+			Pair<TransportProperties, ConnectionHandler> pair =
+					connectable.removeFirst();
+			DuplexTransportConnection d = createConnection(pair.getFirst());
 			if (d != null) {
 				backoff.reset();
-				h.handleConnection(d);
+				pair.getSecond().handleConnection(d);
+			}
+			if (!connectable.isEmpty()) {
+				scheduler.schedule(() -> poll(connectable),
+						CONNECTION_ATTEMPT_INTERVAL_MS, MILLISECONDS);
 			}
 		});
 	}
@@ -339,12 +352,7 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 		if (isNullOrEmpty(uuid)) return null;
 		DuplexTransportConnection conn = connect(address, uuid);
 		if (conn == null) return null;
-		if (connectionLimiter.contactConnectionOpened(conn, false)) {
-			return conn;
-		} else {
-			tryToClose(conn);
-			return null;
-		}
+		return connectionLimiter.contactConnectionOpened(conn) ? conn : null;
 	}
 
 	@Override

bramble-core/src/main/java/org/briarproject/bramble/sync/DuplexOutgoingSession.java

@@ -11,7 +11,6 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.Offer;
@@ -19,7 +18,6 @@ import org.briarproject.bramble.api.sync.Request;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
-import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.sync.event.GroupVisibilityUpdatedEvent;
 import org.briarproject.bramble.api.sync.event.MessageRequestedEvent;
 import org.briarproject.bramble.api.sync.event.MessageSharedEvent;
@@ -73,7 +71,6 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private final EventBus eventBus;
 	private final Clock clock;
 	private final ContactId contactId;
-	private final TransportId transportId;
 	private final int maxLatency, maxIdleTime;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
@@ -89,15 +86,14 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	DuplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, Clock clock, ContactId contactId,
-			TransportId transportId, int maxLatency, int maxIdleTime,
-			StreamWriter streamWriter, SyncRecordWriter recordWriter) {
+			EventBus eventBus, Clock clock, ContactId contactId, int maxLatency,
+			int maxIdleTime, StreamWriter streamWriter,
+			SyncRecordWriter recordWriter) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.clock = clock;
 		this.contactId = contactId;
-		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.maxIdleTime = maxIdleTime;
 		this.streamWriter = streamWriter;
@@ -227,9 +223,6 @@ class DuplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
-		} else if (e instanceof CloseSyncConnectionsEvent) {
-			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
-			if (c.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/sync/SimplexOutgoingSession.java

@@ -11,13 +11,11 @@ import org.briarproject.bramble.api.event.EventListener;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.lifecycle.event.LifecycleEvent;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
 import org.briarproject.bramble.api.sync.SyncSession;
 import org.briarproject.bramble.api.sync.Versions;
-import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
 import org.briarproject.bramble.api.transport.StreamWriter;
 
 import java.io.IOException;
@@ -58,7 +56,6 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private final Executor dbExecutor;
 	private final EventBus eventBus;
 	private final ContactId contactId;
-	private final TransportId transportId;
 	private final int maxLatency;
 	private final StreamWriter streamWriter;
 	private final SyncRecordWriter recordWriter;
@@ -68,14 +65,12 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 	private volatile boolean interrupted = false;
 
 	SimplexOutgoingSession(DatabaseComponent db, Executor dbExecutor,
-			EventBus eventBus, ContactId contactId, TransportId transportId,
-			int maxLatency, StreamWriter streamWriter,
-			SyncRecordWriter recordWriter) {
+			EventBus eventBus, ContactId contactId, int maxLatency,
+			StreamWriter streamWriter, SyncRecordWriter recordWriter) {
 		this.db = db;
 		this.dbExecutor = dbExecutor;
 		this.eventBus = eventBus;
 		this.contactId = contactId;
-		this.transportId = transportId;
 		this.maxLatency = maxLatency;
 		this.streamWriter = streamWriter;
 		this.recordWriter = recordWriter;
@@ -128,9 +123,6 @@ class SimplexOutgoingSession implements SyncSession, EventListener {
 		} else if (e instanceof LifecycleEvent) {
 			LifecycleEvent l = (LifecycleEvent) e;
 			if (l.getLifecycleState() == STOPPING) interrupt();
-		} else if (e instanceof CloseSyncConnectionsEvent) {
-			CloseSyncConnectionsEvent c = (CloseSyncConnectionsEvent) e;
-			if (c.getTransportId().equals(transportId)) interrupt();
 		}
 	}
 

bramble-core/src/main/java/org/briarproject/bramble/sync/SyncSessionFactoryImpl.java

@@ -5,7 +5,6 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.event.EventBus;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.SyncRecordReader;
 import org.briarproject.bramble.api.sync.SyncRecordReaderFactory;
 import org.briarproject.bramble.api.sync.SyncRecordWriter;
@@ -54,23 +53,22 @@ class SyncSessionFactoryImpl implements SyncSessionFactory {
 	}
 
 	@Override
-	public SyncSession createSimplexOutgoingSession(ContactId c, TransportId t,
+	public SyncSession createSimplexOutgoingSession(ContactId c,
 			int maxLatency, StreamWriter streamWriter) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c, t,
+		return new SimplexOutgoingSession(db, dbExecutor, eventBus, c,
 				maxLatency, streamWriter, recordWriter);
 	}
 
 	@Override
-	public SyncSession createDuplexOutgoingSession(ContactId c,
-			TransportId t, int maxLatency, int maxIdleTime,
-			StreamWriter streamWriter) {
+	public SyncSession createDuplexOutgoingSession(ContactId c, int maxLatency,
+			int maxIdleTime, StreamWriter streamWriter) {
 		OutputStream out = streamWriter.getOutputStream();
 		SyncRecordWriter recordWriter =
 				recordWriterFactory.createRecordWriter(out);
-		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c, t,
+		return new DuplexOutgoingSession(db, dbExecutor, eventBus, clock, c,
 				maxLatency, maxIdleTime, streamWriter, recordWriter);
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/system/SystemClock.java

@@ -12,6 +12,11 @@ public class SystemClock implements Clock {
 		return System.currentTimeMillis();
 	}
 
+	@Override
+	public long nanoTime() {
+		return System.nanoTime();
+	}
+
 	@Override
 	public void sleep(long milliseconds) throws InterruptedException {
 		Thread.sleep(milliseconds);

bramble-core/src/test/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

@@ -2420,6 +2420,11 @@ public abstract class JdbcDatabaseTest extends BrambleTestCase {
 			return time;
 		}
 
+		@Override
+		public long nanoTime() {
+			return time * 1_000_000;
+		}
+
 		@Override
 		public void sleep(long milliseconds) throws InterruptedException {
 			Thread.sleep(milliseconds);

bramble-core/src/test/java/org/briarproject/bramble/io/TimeoutInputStreamTest.java

@@ -36,7 +36,7 @@ public class TimeoutInputStreamTest extends BrambleTestCase {
 		in = new UnresponsiveInputStream();
 		listenerCalled = new AtomicBoolean(false);
 		stream = new TimeoutInputStream(new SettableClock(time), in,
-				TIMEOUT_MS, stream -> listenerCalled.set(true));
+				TIMEOUT_MS * 1_000_000, stream -> listenerCalled.set(true));
 		readReturned = new CountDownLatch(1);
 	}
 

bramble-core/src/test/java/org/briarproject/bramble/plugin/bluetooth/BluetoothConnectionLimiterImplTest.java

@@ -1,182 +0,0 @@
-package org.briarproject.bramble.plugin.bluetooth;
-
-import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
-import org.briarproject.bramble.api.sync.event.CloseSyncConnectionsEvent;
-import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.test.BrambleMockTestCase;
-import org.briarproject.bramble.test.SettableClock;
-import org.jmock.Expectations;
-import org.junit.Before;
-import org.junit.Test;
-
-import java.util.concurrent.atomic.AtomicLong;
-
-import static org.briarproject.bramble.plugin.bluetooth.BluetoothConnectionLimiter.MIN_ATTEMPT_INTERVAL_MS;
-import static org.briarproject.bramble.plugin.bluetooth.BluetoothConnectionLimiter.STABILITY_PERIOD_MS;
-import static org.junit.Assert.assertFalse;
-import static org.junit.Assert.assertTrue;
-
-public class BluetoothConnectionLimiterImplTest extends BrambleMockTestCase {
-
-	private final EventBus eventBus = context.mock(EventBus.class);
-
-	private final DuplexTransportConnection conn1 =
-			context.mock(DuplexTransportConnection.class, "conn1");
-	private final DuplexTransportConnection conn2 =
-			context.mock(DuplexTransportConnection.class, "conn2");
-	private final DuplexTransportConnection conn3 =
-			context.mock(DuplexTransportConnection.class, "conn3");
-
-	private final long now = System.currentTimeMillis();
-
-	private AtomicLong time;
-	private BluetoothConnectionLimiter limiter;
-
-	@Before
-	public void setUp() {
-		time = new AtomicLong(now);
-		Clock clock = new SettableClock(time);
-		limiter = new BluetoothConnectionLimiterImpl(eventBus, clock);
-	}
-
-	@Test
-	public void testLimiterDoesNotAllowContactConnectionsDuringKeyAgreement() {
-		assertTrue(limiter.canOpenContactConnection());
-
-		expectCloseSyncConnectionsEvent();
-		limiter.keyAgreementStarted();
-
-		assertFalse(limiter.canOpenContactConnection());
-
-		limiter.keyAgreementEnded();
-
-		assertTrue(limiter.canOpenContactConnection());
-	}
-
-	@Test
-	public void testLimiterAllowsAttemptToRaiseLimitAtStartup() {
-		// First outgoing connection is allowed - we're below the limit of 1
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn1, false));
-
-		// Second outgoing connection is allowed - it's time to try raising
-		// the limit to 2
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn2, false));
-
-		// Third outgoing connection is not allowed - we're above the limit of 1
-		assertFalse(limiter.canOpenContactConnection());
-	}
-
-	@Test
-	public void testLimiterAllowsThirdConnectionAfterFirstTwoAreClosed() {
-		// First outgoing connection is allowed - we're below the limit of 1
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn1, false));
-
-		// Second outgoing connection is allowed - it's time to try raising
-		// the limit to 2
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn2, false));
-
-		// Third outgoing connection is not allowed - we're above the limit of 1
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Close the first connection
-		limiter.connectionClosed(conn1, false);
-
-		// Third outgoing connection is not allowed - we're at the limit of 1
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Close the second connection
-		limiter.connectionClosed(conn2, false);
-
-		// Third outgoing connection is allowed - we're below the limit of 1
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn3, false));
-	}
-
-	@Test
-	public void testLimiterRaisesLimitWhenConnectionsAreStable() {
-		// First outgoing connection is allowed - we're below the limit of 1
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn1, false));
-
-		// Second outgoing connection is allowed - it's time to try raising
-		// the limit to 2
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn2, false));
-
-		// Third outgoing connection is not allowed - we're above the limit of 1
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Time passes
-		time.set(now + STABILITY_PERIOD_MS);
-
-		// Third outgoing connection is still not allowed - first two are now
-		// stable so limit is raised to 2, but we're already at the new limit
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Time passes
-		time.set(now + MIN_ATTEMPT_INTERVAL_MS);
-
-		// Third outgoing connection is allowed - it's time to try raising
-		// the limit to 3
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn3, false));
-
-		// Fourth outgoing connection is not allowed - we're above the limit
-		// of 2
-		assertFalse(limiter.canOpenContactConnection());
-	}
-
-	@Test
-	public void testLimiterIncreasesIntervalWhenConnectionFailsAboveLimit() {
-		// First outgoing connection is allowed - we're below the limit of 1
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn1, false));
-
-		// Time passes
-		time.set(now + 1);
-
-		// Second outgoing connection is allowed - it's time to try raising
-		// the limit to 2
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn2, false));
-
-		// Time passes - the first connection is stable, the second isn't
-		time.set(now + STABILITY_PERIOD_MS);
-
-		// First connection fails. The second connection isn't stable yet, so
-		// the limiter considers this a failed attempt and doubles the interval
-		// between attempts
-		limiter.connectionClosed(conn1, true);
-
-		// Third outgoing connection is not allowed - we're still at the limit
-		// of 1
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Time passes - nearly time for the second attempt
-		time.set(now + MIN_ATTEMPT_INTERVAL_MS * 2);
-
-		// Third outgoing connection is not allowed - we're still at the limit
-		// of 1
-		assertFalse(limiter.canOpenContactConnection());
-
-		// Time passes - now it's time for the second attempt
-		time.set(now + 1 + MIN_ATTEMPT_INTERVAL_MS * 2);
-
-		// Third outgoing connection is allowed - it's time to try raising the
-		// limit to 2 again
-		assertTrue(limiter.canOpenContactConnection());
-		assertTrue(limiter.contactConnectionOpened(conn3, false));
-	}
-
-	private void expectCloseSyncConnectionsEvent() {
-		context.checking(new Expectations() {{
-			oneOf(eventBus).broadcast(with(any(
-					CloseSyncConnectionsEvent.class)));
-		}});
-	}
-}

bramble-core/src/test/java/org/briarproject/bramble/sync/SimplexOutgoingSessionTest.java

@@ -4,7 +4,6 @@ import org.briarproject.bramble.api.contact.ContactId;
 import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.event.EventBus;
-import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.sync.Ack;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
@@ -24,7 +23,6 @@ import static org.briarproject.bramble.api.sync.SyncConstants.MAX_MESSAGE_IDS;
 import static org.briarproject.bramble.test.TestUtils.getContactId;
 import static org.briarproject.bramble.test.TestUtils.getMessage;
 import static org.briarproject.bramble.test.TestUtils.getRandomId;
-import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
 public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
@@ -38,15 +36,14 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 
 	private final Executor dbExecutor = new ImmediateExecutor();
 	private final ContactId contactId = getContactId();
-	private final TransportId transportId = getTransportId();
 	private final Message message = getMessage(new GroupId(getRandomId()));
 	private final MessageId messageId = message.getId();
 
 	@Test
 	public void testNothingToSend() throws Exception {
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
-				streamWriter, recordWriter);
+				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
+				recordWriter);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction noMsgTxn = new Transaction(null, false);
 
@@ -79,8 +76,8 @@ public class SimplexOutgoingSessionTest extends BrambleMockTestCase {
 	public void testSomethingToSend() throws Exception {
 		Ack ack = new Ack(singletonList(messageId));
 		SimplexOutgoingSession session = new SimplexOutgoingSession(db,
-				dbExecutor, eventBus, contactId, transportId, MAX_LATENCY,
-				streamWriter, recordWriter);
+				dbExecutor, eventBus, contactId, MAX_LATENCY, streamWriter,
+				recordWriter);
 		Transaction ackTxn = new Transaction(null, false);
 		Transaction noAckTxn = new Transaction(null, false);
 		Transaction msgTxn = new Transaction(null, false);

bramble-java/src/main/java/org/briarproject/bramble/plugin/DesktopPluginModule.java

@@ -10,7 +10,7 @@ import org.briarproject.bramble.api.plugin.PluginConfig;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.plugin.simplex.SimplexPluginFactory;
 import org.briarproject.bramble.api.reliability.ReliabilityLayerFactory;
-import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.Scheduler;
 import org.briarproject.bramble.plugin.bluetooth.JavaBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.modem.ModemPluginFactory;
 import org.briarproject.bramble.plugin.tcp.LanTcpPluginFactory;
@@ -19,6 +19,7 @@ import org.briarproject.bramble.plugin.tcp.WanTcpPluginFactory;
 import java.security.SecureRandom;
 import java.util.Collection;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 
 import dagger.Module;
 import dagger.Provides;
@@ -31,12 +32,13 @@ public class DesktopPluginModule extends PluginModule {
 
 	@Provides
 	PluginConfig getPluginConfig(@IoExecutor Executor ioExecutor,
+			@Scheduler ScheduledExecutorService scheduler,
 			SecureRandom random, BackoffFactory backoffFactory,
 			ReliabilityLayerFactory reliabilityFactory,
-			ShutdownManager shutdownManager, EventBus eventBus, Clock clock,
+			ShutdownManager shutdownManager, EventBus eventBus,
 			TimeoutMonitor timeoutMonitor) {
 		DuplexPluginFactory bluetooth = new JavaBluetoothPluginFactory(
-				ioExecutor, random, eventBus, clock, timeoutMonitor,
+				ioExecutor, scheduler, random, eventBus, timeoutMonitor,
 				backoffFactory);
 		DuplexPluginFactory modem = new ModemPluginFactory(ioExecutor,
 				reliabilityFactory);

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothPlugin.java

@@ -10,6 +10,7 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import java.io.IOException;
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
@@ -36,10 +37,11 @@ class JavaBluetoothPlugin extends BluetoothPlugin<StreamConnectionNotifier> {
 
 	JavaBluetoothPlugin(BluetoothConnectionLimiter connectionManager,
 			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			SecureRandom secureRandom, Backoff backoff,
-			PluginCallback callback, int maxLatency, int maxIdleTime) {
-		super(connectionManager, timeoutMonitor, ioExecutor, secureRandom,
-				backoff, callback, maxLatency, maxIdleTime);
+			ScheduledExecutorService scheduler, SecureRandom secureRandom,
+			Backoff backoff, PluginCallback callback, int maxLatency,
+			int maxIdleTime) {
+		super(connectionManager, timeoutMonitor, ioExecutor, scheduler,
+				secureRandom, backoff, callback, maxLatency, maxIdleTime);
 	}
 
 	@Override

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothPluginFactory.java

@@ -9,10 +9,10 @@ import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
-import org.briarproject.bramble.api.system.Clock;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
+import java.util.concurrent.ScheduledExecutorService;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -29,19 +29,20 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
+	private final ScheduledExecutorService scheduler;
 	private final SecureRandom secureRandom;
 	private final EventBus eventBus;
-	private final Clock clock;
 	private final TimeoutMonitor timeoutMonitor;
 	private final BackoffFactory backoffFactory;
 
 	public JavaBluetoothPluginFactory(Executor ioExecutor,
-			SecureRandom secureRandom, EventBus eventBus, Clock clock,
-			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
+			ScheduledExecutorService scheduler, SecureRandom secureRandom,
+			EventBus eventBus, TimeoutMonitor timeoutMonitor,
+			BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
+		this.scheduler = scheduler;
 		this.secureRandom = secureRandom;
 		this.eventBus = eventBus;
-		this.clock = clock;
 		this.timeoutMonitor = timeoutMonitor;
 		this.backoffFactory = backoffFactory;
 	}
@@ -59,12 +60,12 @@ public class JavaBluetoothPluginFactory implements DuplexPluginFactory {
 	@Override
 	public DuplexPlugin createPlugin(PluginCallback callback) {
 		BluetoothConnectionLimiter connectionLimiter =
-				new BluetoothConnectionLimiterImpl(eventBus, clock);
+				new BluetoothConnectionLimiterImpl();
 		Backoff backoff = backoffFactory.createBackoff(MIN_POLLING_INTERVAL,
 				MAX_POLLING_INTERVAL, BACKOFF_BASE);
 		JavaBluetoothPlugin plugin = new JavaBluetoothPlugin(connectionLimiter,
-				timeoutMonitor, ioExecutor, secureRandom, backoff, callback,
-				MAX_LATENCY, MAX_IDLE_TIME);
+				timeoutMonitor, ioExecutor, scheduler, secureRandom, backoff,
+				callback, MAX_LATENCY, MAX_IDLE_TIME);
 		eventBus.addListener(plugin);
 		return plugin;
 	}

bramble-java/src/main/java/org/briarproject/bramble/plugin/bluetooth/JavaBluetoothTransportConnection.java

@@ -45,7 +45,7 @@ class JavaBluetoothTransportConnection
 		try {
 			stream.close();
 		} finally {
-			connectionLimiter.connectionClosed(this, exception);
+			connectionLimiter.connectionClosed(this);
 		}
 	}
 }

briar-android/src/main/java/org/briarproject/briar/android/AppModule.java

@@ -127,8 +127,8 @@ public class AppModule {
 			TimeoutMonitor timeoutMonitor) {
 		Context appContext = app.getApplicationContext();
 		DuplexPluginFactory bluetooth = new AndroidBluetoothPluginFactory(
-				ioExecutor, androidExecutor, appContext, random, eventBus,
-				clock, timeoutMonitor, backoffFactory);
+				ioExecutor, scheduler, androidExecutor, appContext, random,
+				eventBus, clock, timeoutMonitor, backoffFactory);
 		DuplexPluginFactory tor = new AndroidTorPluginFactory(ioExecutor,
 				scheduler, appContext, networkManager, locationUtils, eventBus,
 				torSocketFactory, backoffFactory, resourceProvider,