Pause between connection attempts.

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

@@ -28,7 +28,9 @@ import org.briarproject.bramble.api.system.Scheduler;
 import java.security.SecureRandom;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
 import java.util.concurrent.ScheduledExecutorService;
@@ -58,6 +60,7 @@ class Poller implements EventListener {
 	private final Clock clock;
 	private final Lock lock;
 	private final Map<TransportId, ScheduledPollTask> tasks; // Locking: lock
+	private final Set<TransportId> polling; // Locking: lock
 
 	Poller(@IoExecutor Executor ioExecutor,
 			@Scheduler ScheduledExecutorService scheduler,
@@ -75,6 +78,7 @@ class Poller implements EventListener {
 		this.clock = clock;
 		lock = new ReentrantLock();
 		tasks = new HashMap<>();
+		polling = new HashSet<>();
 	}
 
 	@Override
@@ -241,20 +245,33 @@ class Poller implements EventListener {
 		@Override
 		@IoExecutor
 		public void run() {
+			TransportId t = plugin.getId();
+			boolean shouldPoll;
 			lock.lock();
 			try {
-				TransportId t = plugin.getId();
 				ScheduledPollTask scheduled = tasks.get(t);
 				if (scheduled != null && scheduled.task != this)
 					return; // Replaced by another task
 				tasks.remove(t);
+				// Don't poll again if last poll is still running
+				shouldPoll = polling.add(t);
 			} finally {
 				lock.unlock();
 			}
 			int delay = plugin.getPollingInterval();
 			if (randomiseNext) delay = (int) (delay * random.nextDouble());
 			schedule(plugin, delay, false);
-			poll(plugin);
+			if (shouldPoll) {
+				poll(plugin);
+			} else if (LOG.isLoggable(INFO)) {
+				LOG.info("Last poll for " + t + " is still running");
+			}
+			lock.lock();
+			try {
+				polling.remove(t);
+			} finally {
+				lock.unlock();
+			}
 		}
 	}
 }

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

@@ -26,8 +26,10 @@ import org.briarproject.bramble.util.StringUtils;
 
 import java.io.IOException;
 import java.security.SecureRandom;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
 import java.util.Map;
-import java.util.Map.Entry;
 import java.util.UUID;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
@@ -52,6 +54,12 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	private static final Logger LOG =
 			Logger.getLogger(BluetoothPlugin.class.getName());
 
+	/**
+	 * How many milliseconds to pause between connection attempts when
+	 * polling, to avoid interfering with other Bluetooth or wifi connections.
+	 */
+	private static final int POLLING_PAUSE_MS = 1000;
+
 	final BluetoothConnectionLimiter connectionLimiter;
 
 	private final Executor ioExecutor;
@@ -252,24 +260,39 @@ abstract class BluetoothPlugin<SS> implements DuplexPlugin, EventListener {
 	public void poll(Map<ContactId, TransportProperties> contacts) {
 		if (!isRunning() || !shouldAllowContactConnections()) return;
 		backoff.increment();
-		// Try to connect to known devices in parallel
-		for (Entry<ContactId, TransportProperties> e : contacts.entrySet()) {
-			String address = e.getValue().get(PROP_ADDRESS);
-			if (StringUtils.isNullOrEmpty(address)) continue;
-			String uuid = e.getValue().get(PROP_UUID);
-			if (StringUtils.isNullOrEmpty(uuid)) continue;
-			ContactId c = e.getKey();
-			ioExecutor.execute(() -> {
+		// Try to connect to known devices in a random order
+		List<ContactId> keys = new ArrayList<>(contacts.keySet());
+		Collections.shuffle(keys);
+		ioExecutor.execute(() -> {
+			boolean first = true;
+			for (ContactId c : keys) {
 				if (!isRunning() || !shouldAllowContactConnections()) return;
 				if (!connectionLimiter.canOpenContactConnection()) return;
+				TransportProperties p = contacts.get(c);
+				String address = p.get(PROP_ADDRESS);
+				if (StringUtils.isNullOrEmpty(address)) continue;
+				String uuid = p.get(PROP_UUID);
+				if (StringUtils.isNullOrEmpty(uuid)) continue;
+				// Pause between connection attempts
+				if (first) {
+					first = false;
+				} else {
+					try {
+						Thread.sleep(POLLING_PAUSE_MS);
+					} catch (InterruptedException ex) {
+						LOG.info("Interrupted while polling");
+						Thread.currentThread().interrupt();
+						return;
+					}
+				}
 				DuplexTransportConnection conn = connect(address, uuid);
 				if (conn != null) {
 					backoff.reset();
 					if (connectionLimiter.contactConnectionOpened(conn))
 						callback.outgoingConnectionCreated(c, conn);
 				}
-			});
-		}
+			}
+		});
 	}
 
 	@Nullable