Wrap scheduler in an interface.

bramble-android/src/main/java/org/briarproject/bramble/network/AndroidNetworkManager.java

@@ -15,10 +15,9 @@ import org.briarproject.bramble.api.network.NetworkStatus;
 import org.briarproject.bramble.api.network.event.NetworkStatusEvent;
 import org.briarproject.bramble.api.nullsafety.MethodsNotNullByDefault;
 import org.briarproject.bramble.api.nullsafety.ParametersNotNullByDefault;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicReference;
@@ -50,7 +49,7 @@ class AndroidNetworkManager implements NetworkManager, Service {
 	private static final String WIFI_AP_STATE_CHANGED_ACTION =
 			"android.net.wifi.WIFI_AP_STATE_CHANGED";
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final EventBus eventBus;
 	private final Context appContext;
 	private final AtomicReference<Future<?>> connectivityCheck =
@@ -60,8 +59,8 @@ class AndroidNetworkManager implements NetworkManager, Service {
 	private volatile BroadcastReceiver networkStateReceiver = null;
 
 	@Inject
-	AndroidNetworkManager(@Scheduler ScheduledExecutorService scheduler,
-			EventBus eventBus, Application app) {
+	AndroidNetworkManager(TaskScheduler scheduler, EventBus eventBus,
+			Application app) {
 		this.scheduler = scheduler;
 		this.eventBus = eventBus;
 		this.appContext = app.getApplicationContext();

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

@@ -18,6 +18,7 @@ import org.briarproject.bramble.api.plugin.PluginException;
 import org.briarproject.bramble.api.plugin.duplex.DuplexTransportConnection;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.util.AndroidUtils;
 import org.briarproject.bramble.util.IoUtils;
 
@@ -31,7 +32,6 @@ 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;
@@ -67,7 +67,7 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 
 	private static final int MAX_DISCOVERY_MS = 10_000;
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final AndroidExecutor androidExecutor;
 	private final Context appContext;
 	private final Clock clock;
@@ -79,10 +79,16 @@ class AndroidBluetoothPlugin extends BluetoothPlugin<BluetoothServerSocket> {
 	private volatile BluetoothAdapter adapter = null;
 
 	AndroidBluetoothPlugin(BluetoothConnectionLimiter connectionLimiter,
-			TimeoutMonitor timeoutMonitor, Executor ioExecutor,
-			SecureRandom secureRandom, ScheduledExecutorService scheduler,
-			AndroidExecutor androidExecutor, Context appContext, Clock clock,
-			Backoff backoff, PluginCallback callback, int maxLatency,
+			TimeoutMonitor timeoutMonitor,
+			Executor ioExecutor,
+			SecureRandom secureRandom,
+			TaskScheduler scheduler,
+			AndroidExecutor androidExecutor,
+			Context appContext,
+			Clock clock,
+			Backoff backoff,
+			PluginCallback callback,
+			int maxLatency,
 			int maxIdleTime) {
 		super(connectionLimiter, timeoutMonitor, ioExecutor, secureRandom,
 				backoff, callback, maxLatency, maxIdleTime);

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

@@ -13,10 +13,10 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPlugin;
 import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.security.SecureRandom;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.annotation.concurrent.Immutable;
 
@@ -33,7 +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 TaskScheduler scheduler;
 	private final AndroidExecutor androidExecutor;
 	private final Context appContext;
 	private final SecureRandom secureRandom;
@@ -43,10 +43,14 @@ public class AndroidBluetoothPluginFactory implements DuplexPluginFactory {
 	private final BackoffFactory backoffFactory;
 
 	public AndroidBluetoothPluginFactory(Executor ioExecutor,
-			ScheduledExecutorService scheduler,
-			AndroidExecutor androidExecutor, Context appContext,
-			SecureRandom secureRandom, EventBus eventBus, Clock clock,
-			TimeoutMonitor timeoutMonitor, BackoffFactory backoffFactory) {
+			TaskScheduler scheduler,
+			AndroidExecutor androidExecutor,
+			Context appContext,
+			SecureRandom secureRandom,
+			EventBus eventBus,
+			Clock clock,
+			TimeoutMonitor timeoutMonitor,
+			BackoffFactory backoffFactory) {
 		this.ioExecutor = ioExecutor;
 		this.scheduler = scheduler;
 		this.androidExecutor = androidExecutor;

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

@@ -8,12 +8,12 @@ import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.Plugin;
 import org.briarproject.bramble.api.plugin.duplex.AbstractDuplexTransportConnection;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.util.RenewableWakeLock;
 
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
-import java.util.concurrent.ScheduledExecutorService;
 
 import static android.content.Context.POWER_SERVICE;
 import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
@@ -34,9 +34,10 @@ class AndroidBluetoothTransportConnection
 
 	AndroidBluetoothTransportConnection(Plugin plugin,
 			BluetoothConnectionLimiter connectionLimiter,
-			TimeoutMonitor timeoutMonitor, Context appContext,
-			ScheduledExecutorService scheduler, BluetoothSocket socket)
-			throws IOException {
+			TimeoutMonitor timeoutMonitor,
+			Context appContext,
+			TaskScheduler scheduler,
+			BluetoothSocket socket) throws IOException {
 		super(plugin);
 		this.connectionLimiter = connectionLimiter;
 		this.socket = socket;

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPlugin.java

@@ -15,11 +15,11 @@ import org.briarproject.bramble.api.plugin.PluginCallback;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.util.RenewableWakeLock;
 
 import java.io.IOException;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.net.SocketFactory;
 
@@ -36,18 +36,26 @@ class AndroidTorPlugin extends TorPlugin {
 	private final Context appContext;
 	private final RenewableWakeLock wakeLock;
 
-	AndroidTorPlugin(Executor ioExecutor, ScheduledExecutorService scheduler,
-			Context appContext, NetworkManager networkManager,
-			LocationUtils locationUtils, SocketFactory torSocketFactory,
-			Clock clock, ResourceProvider resourceProvider,
+	AndroidTorPlugin(Executor ioExecutor,
+			TaskScheduler scheduler,
+			Context appContext,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			SocketFactory torSocketFactory,
+			Clock clock,
+			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
-			BatteryManager batteryManager, Backoff backoff,
+			BatteryManager batteryManager,
+			Backoff backoff,
 			TorRendezvousCrypto torRendezvousCrypto,
-			PluginCallback callback, String architecture, int maxLatency,
+			PluginCallback callback,
+			String architecture,
+			int maxLatency,
 			int maxIdleTime) {
 		super(ioExecutor, networkManager, locationUtils, torSocketFactory,
 				clock, resourceProvider, circumventionProvider, batteryManager,
-				backoff, torRendezvousCrypto, callback, architecture, maxLatency, maxIdleTime,
+				backoff, torRendezvousCrypto, callback, architecture,
+				maxLatency, maxIdleTime,
 				appContext.getDir("tor", MODE_PRIVATE));
 		this.appContext = appContext;
 		PowerManager pm = (PowerManager)

bramble-android/src/main/java/org/briarproject/bramble/plugin/tor/AndroidTorPluginFactory.java

@@ -16,10 +16,10 @@ import org.briarproject.bramble.api.plugin.duplex.DuplexPluginFactory;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.util.AndroidUtils;
 
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.Immutable;
@@ -39,7 +39,7 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private static final double BACKOFF_BASE = 1.2;
 
 	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Context appContext;
 	private final NetworkManager networkManager;
 	private final LocationUtils locationUtils;
@@ -52,12 +52,17 @@ public class AndroidTorPluginFactory implements DuplexPluginFactory {
 	private final Clock clock;
 
 	public AndroidTorPluginFactory(Executor ioExecutor,
-			ScheduledExecutorService scheduler, Context appContext,
-			NetworkManager networkManager, LocationUtils locationUtils,
-			EventBus eventBus, SocketFactory torSocketFactory,
-			BackoffFactory backoffFactory, ResourceProvider resourceProvider,
+			TaskScheduler scheduler,
+			Context appContext,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			EventBus eventBus,
+			SocketFactory torSocketFactory,
+			BackoffFactory backoffFactory,
+			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
-			BatteryManager batteryManager, Clock clock) {
+			BatteryManager batteryManager,
+			Clock clock) {
 		this.ioExecutor = ioExecutor;
 		this.scheduler = scheduler;
 		this.appContext = appContext;

bramble-android/src/main/java/org/briarproject/bramble/util/RenewableWakeLock.java

@@ -3,8 +3,8 @@ package org.briarproject.bramble.util;
 import android.os.PowerManager;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 import java.util.concurrent.TimeUnit;
 import java.util.logging.Logger;
@@ -29,7 +29,7 @@ public class RenewableWakeLock {
 	private static final int SAFETY_MARGIN_MS = 10_000;
 
 	private final PowerManager powerManager;
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final int levelAndFlags;
 	private final String tag;
 	private final long durationMs;
@@ -39,10 +39,10 @@ public class RenewableWakeLock {
 	@Nullable
 	private PowerManager.WakeLock wakeLock; // Locking: lock
 	@Nullable
-	private ScheduledFuture future; // Locking: lock
+	private ScheduledFuture<?> future; // Locking: lock
 
 	public RenewableWakeLock(PowerManager powerManager,
-			ScheduledExecutorService scheduler, int levelAndFlags, String tag,
+			TaskScheduler scheduler, int levelAndFlags, String tag,
 			long duration, TimeUnit timeUnit) {
 		this.powerManager = powerManager;
 		this.scheduler = scheduler;

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

@@ -1,25 +0,0 @@
-package org.briarproject.bramble.api.system;
-
-import java.lang.annotation.Retention;
-import java.lang.annotation.Target;
-
-import javax.inject.Qualifier;
-
-import static java.lang.annotation.ElementType.FIELD;
-import static java.lang.annotation.ElementType.METHOD;
-import static java.lang.annotation.ElementType.PARAMETER;
-import static java.lang.annotation.RetentionPolicy.RUNTIME;
-
-/**
- * Annotation for injecting a scheduled executor service
- * that can be used to schedule the execution of tasks.
- * <p>
- * The service should <b>only</b> be used for running tasks on other executors
- * at scheduled times.
- * No significant work should be run by the service itself!
- */
-@Qualifier
-@Target({FIELD, METHOD, PARAMETER})
-@Retention(RUNTIME)
-public @interface Scheduler {
-}

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

@@ -0,0 +1,34 @@
+package org.briarproject.bramble.api.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * A service that can be used to schedule the execution of tasks.
+ * <p>
+ * The service should only be used for running tasks on other executors
+ * at scheduled times. No significant work should be run by the service itself.
+ */
+@NotNullByDefault
+public interface TaskScheduler {
+
+	/**
+	 * See {@link ScheduledExecutorService#schedule(Runnable, long, TimeUnit)}.
+	 */
+	ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit);
+
+	/**
+	 * See {@link ScheduledExecutorService#scheduleAtFixedRate(Runnable, long, long, TimeUnit)}.
+	 */
+	ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long delay,
+			long interval, TimeUnit unit);
+
+	/**
+	 * See {@link ScheduledExecutorService#scheduleWithFixedDelay(Runnable, long, long, TimeUnit)}.
+	 */
+	ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay,
+			long interval, TimeUnit unit);
+}

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

@@ -3,7 +3,7 @@ package org.briarproject.bramble.io;
 import org.briarproject.bramble.api.io.TimeoutMonitor;
 import org.briarproject.bramble.api.lifecycle.IoExecutor;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.io.IOException;
 import java.io.InputStream;
@@ -11,7 +11,6 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
 import javax.annotation.concurrent.GuardedBy;
@@ -30,7 +29,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 
 	private static final long CHECK_INTERVAL_MS = SECONDS.toMillis(10);
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Executor ioExecutor;
 	private final Clock clock;
 	private final Object lock = new Object();
@@ -41,7 +40,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 	private Future<?> task = null;
 
 	@Inject
-	TimeoutMonitorImpl(@Scheduler ScheduledExecutorService scheduler,
+	TimeoutMonitorImpl(TaskScheduler scheduler,
 			@IoExecutor Executor ioExecutor, Clock clock) {
 		this.scheduler = scheduler;
 		this.ioExecutor = ioExecutor;
@@ -74,7 +73,7 @@ class TimeoutMonitorImpl implements TimeoutMonitor {
 		if (toCancel != null) toCancel.cancel(false);
 	}
 
-	@Scheduler
+	// Scheduler
 	private void checkTimeouts() {
 		ioExecutor.execute(() -> {
 			List<TimeoutInputStream> snapshot;

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

@@ -26,7 +26,7 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.security.SecureRandom;
 import java.util.ArrayList;
@@ -36,7 +36,6 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.concurrent.Executor;
 import java.util.concurrent.Future;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.locks.Lock;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
@@ -58,7 +57,7 @@ class PollerImpl implements Poller, EventListener {
 	private static final Logger LOG = getLogger(PollerImpl.class.getName());
 
 	private final Executor ioExecutor;
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final ConnectionManager connectionManager;
 	private final ConnectionRegistry connectionRegistry;
 	private final PluginManager pluginManager;
@@ -71,11 +70,13 @@ class PollerImpl implements Poller, EventListener {
 
 	@Inject
 	PollerImpl(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler,
+			TaskScheduler scheduler,
 			ConnectionManager connectionManager,
-			ConnectionRegistry connectionRegistry, PluginManager pluginManager,
+			ConnectionRegistry connectionRegistry,
+			PluginManager pluginManager,
 			TransportPropertyManager transportPropertyManager,
-			SecureRandom random, Clock clock) {
+			SecureRandom random,
+			Clock clock) {
 		this.ioExecutor = ioExecutor;
 		this.scheduler = scheduler;
 		this.connectionManager = connectionManager;

bramble-core/src/main/java/org/briarproject/bramble/rendezvous/RendezvousPollerImpl.java

@@ -41,7 +41,7 @@ import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedE
 import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
 import org.briarproject.bramble.api.rendezvous.event.RendezvousPollEvent;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.security.GeneralSecurityException;
 import java.util.ArrayList;
@@ -52,7 +52,6 @@ import java.util.Map;
 import java.util.Map.Entry;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
@@ -80,7 +79,7 @@ class RendezvousPollerImpl implements RendezvousPoller, Service, EventListener {
 	private static final Logger LOG =
 			getLogger(RendezvousPollerImpl.class.getName());
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final DatabaseComponent db;
 	private final IdentityManager identityManager;
 	private final TransportCrypto transportCrypto;
@@ -105,7 +104,7 @@ class RendezvousPollerImpl implements RendezvousPoller, Service, EventListener {
 
 	@Inject
 	RendezvousPollerImpl(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler,
+			TaskScheduler scheduler,
 			DatabaseComponent db,
 			IdentityManager identityManager,
 			TransportCrypto transportCrypto,
@@ -205,7 +204,7 @@ class RendezvousPollerImpl implements RendezvousPoller, Service, EventListener {
 		return plugin.createRendezvousEndpoint(k, cs.alice, h);
 	}
 
-	@Scheduler
+	// Scheduler
 	private void poll() {
 		worker.execute(() -> {
 			removeExpiredPendingContacts();

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

@@ -2,7 +2,7 @@ package org.briarproject.bramble.system;
 
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.util.concurrent.RejectedExecutionHandler;
 import java.util.concurrent.ScheduledExecutorService;
@@ -19,17 +19,16 @@ public class SystemModule {
 
 	public static class EagerSingletons {
 		@Inject
-		@Scheduler
-		ScheduledExecutorService scheduledExecutorService;
+		TaskScheduler scheduler;
 	}
 
-	private final ScheduledExecutorService scheduler;
+	private final ScheduledExecutorService scheduledExecutorService;
 
 	public SystemModule() {
 		// Discard tasks that are submitted during shutdown
 		RejectedExecutionHandler policy =
 				new ScheduledThreadPoolExecutor.DiscardPolicy();
-		scheduler = new ScheduledThreadPoolExecutor(1, policy);
+		scheduledExecutorService = new ScheduledThreadPoolExecutor(1, policy);
 	}
 
 	@Provides
@@ -39,10 +38,8 @@ public class SystemModule {
 
 	@Provides
 	@Singleton
-	@Scheduler
-	ScheduledExecutorService provideScheduledExecutorService(
-			LifecycleManager lifecycleManager) {
-		lifecycleManager.registerForShutdown(scheduler);
-		return scheduler;
+	TaskScheduler provideTaskScheduler(LifecycleManager lifecycleManager) {
+		lifecycleManager.registerForShutdown(scheduledExecutorService);
+		return new TaskSchedulerImpl(scheduledExecutorService);
 	}
 }

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

@@ -0,0 +1,43 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.TaskScheduler;
+
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * A {@link TaskScheduler} that delegates all calls to a
+ * {@link ScheduledExecutorService}.
+ */
+@ThreadSafe
+@NotNullByDefault
+class TaskSchedulerImpl implements TaskScheduler {
+
+	private final ScheduledExecutorService delegate;
+
+	TaskSchedulerImpl(ScheduledExecutorService delegate) {
+		this.delegate = delegate;
+	}
+
+	@Override
+	public ScheduledFuture<?> schedule(Runnable task, long delay,
+			TimeUnit unit) {
+		return delegate.schedule(task, delay, unit);
+	}
+
+	@Override
+	public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long delay,
+			long interval, TimeUnit unit) {
+		return delegate.scheduleAtFixedRate(task, delay, interval, unit);
+	}
+
+	@Override
+	public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay,
+			long interval, TimeUnit unit) {
+		return delegate.scheduleWithFixedDelay(task, delay, interval, unit);
+	}
+}

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManagerFactoryImpl.java

@@ -6,10 +6,9 @@ import org.briarproject.bramble.api.db.DatabaseExecutor;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
@@ -22,14 +21,15 @@ class TransportKeyManagerFactoryImpl implements
 	private final DatabaseComponent db;
 	private final TransportCrypto transportCrypto;
 	private final Executor dbExecutor;
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Clock clock;
 
 	@Inject
 	TransportKeyManagerFactoryImpl(DatabaseComponent db,
 			TransportCrypto transportCrypto,
 			@DatabaseExecutor Executor dbExecutor,
-			@Scheduler ScheduledExecutorService scheduler, Clock clock) {
+			TaskScheduler scheduler,
+			Clock clock) {
 		this.db = db;
 		this.transportCrypto = transportCrypto;
 		this.dbExecutor = dbExecutor;

bramble-core/src/main/java/org/briarproject/bramble/transport/TransportKeyManagerImpl.java

@@ -11,7 +11,7 @@ import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.StreamContext;
 import org.briarproject.bramble.api.transport.TransportKeySet;
@@ -24,7 +24,6 @@ import java.util.HashMap;
 import java.util.Iterator;
 import java.util.Map;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.locks.ReentrantLock;
 import java.util.logging.Logger;
@@ -53,7 +52,7 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 	private final DatabaseComponent db;
 	private final TransportCrypto transportCrypto;
 	private final Executor dbExecutor;
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Clock clock;
 	private final TransportId transportId;
 	private final long timePeriodLength;
@@ -72,9 +71,12 @@ class TransportKeyManagerImpl implements TransportKeyManager {
 			pendingContactOutContexts = new HashMap<>();
 
 	TransportKeyManagerImpl(DatabaseComponent db,
-			TransportCrypto transportCrypto, Executor dbExecutor,
-			@Scheduler ScheduledExecutorService scheduler, Clock clock,
-			TransportId transportId, long maxLatency) {
+			TransportCrypto transportCrypto,
+			Executor dbExecutor,
+			TaskScheduler scheduler,
+			Clock clock,
+			TransportId transportId,
+			long maxLatency) {
 		this.db = db;
 		this.transportCrypto = transportCrypto;
 		this.dbExecutor = dbExecutor;

bramble-core/src/test/java/org/briarproject/bramble/plugin/PollerImplTest.java

@@ -19,6 +19,7 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.properties.TransportProperties;
 import org.briarproject.bramble.api.properties.TransportPropertyManager;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.briarproject.bramble.test.RunAction;
@@ -30,7 +31,6 @@ import org.junit.Test;
 import java.security.SecureRandom;
 import java.util.List;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.ScheduledFuture;
 
 import static java.util.Arrays.asList;
@@ -45,8 +45,7 @@ import static org.briarproject.bramble.test.TestUtils.getTransportId;
 
 public class PollerImplTest extends BrambleMockTestCase {
 
-	private final ScheduledExecutorService scheduler =
-			context.mock(ScheduledExecutorService.class);
+	private final TaskScheduler scheduler = context.mock(TaskScheduler.class);
 	private final ConnectionManager connectionManager =
 			context.mock(ConnectionManager.class);
 	private final ConnectionRegistry connectionRegistry =
@@ -56,7 +55,8 @@ public class PollerImplTest extends BrambleMockTestCase {
 	private final TransportPropertyManager transportPropertyManager =
 			context.mock(TransportPropertyManager.class);
 	private final Clock clock = context.mock(Clock.class);
-	private final ScheduledFuture future = context.mock(ScheduledFuture.class);
+	private final ScheduledFuture<?> future =
+			context.mock(ScheduledFuture.class);
 	private final SecureRandom random;
 
 	private final Executor ioExecutor = new ImmediateExecutor();

bramble-core/src/test/java/org/briarproject/bramble/rendezvous/RendezvousPollerImplTest.java

@@ -26,6 +26,7 @@ import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionClosedE
 import org.briarproject.bramble.api.rendezvous.event.RendezvousConnectionOpenedEvent;
 import org.briarproject.bramble.api.rendezvous.event.RendezvousPollEvent;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.CaptureArgumentAction;
 import org.briarproject.bramble.test.DbExpectations;
@@ -37,7 +38,6 @@ import org.junit.Test;
 
 import java.util.Random;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicReference;
 
 import static java.util.Collections.emptyList;
@@ -60,8 +60,7 @@ import static org.briarproject.bramble.test.TestUtils.getTransportProperties;
 
 public class RendezvousPollerImplTest extends BrambleMockTestCase {
 
-	private final ScheduledExecutorService scheduler =
-			context.mock(ScheduledExecutorService.class);
+	private final TaskScheduler scheduler = context.mock(TaskScheduler.class);
 	private final DatabaseComponent db = context.mock(DatabaseComponent.class);
 	private final IdentityManager identityManager =
 			context.mock(IdentityManager.class);

bramble-core/src/test/java/org/briarproject/bramble/transport/TransportKeyManagerImplTest.java

@@ -8,6 +8,7 @@ import org.briarproject.bramble.api.db.DatabaseComponent;
 import org.briarproject.bramble.api.db.Transaction;
 import org.briarproject.bramble.api.plugin.TransportId;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.api.transport.IncomingKeys;
 import org.briarproject.bramble.api.transport.KeySetId;
 import org.briarproject.bramble.api.transport.OutgoingKeys;
@@ -29,7 +30,6 @@ import java.util.Collection;
 import java.util.List;
 import java.util.Random;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import static java.util.Arrays.asList;
 import static java.util.Collections.singletonList;
@@ -55,8 +55,7 @@ public class TransportKeyManagerImplTest extends BrambleMockTestCase {
 	private final TransportCrypto transportCrypto =
 			context.mock(TransportCrypto.class);
 	private final Executor dbExecutor = context.mock(Executor.class);
-	private final ScheduledExecutorService scheduler =
-			context.mock(ScheduledExecutorService.class);
+	private final TaskScheduler scheduler = context.mock(TaskScheduler.class);
 	private final Clock clock = context.mock(Clock.class);
 
 	private final TransportId transportId = getTransportId();

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

@@ -31,7 +31,7 @@ import org.briarproject.bramble.api.system.AndroidExecutor;
 import org.briarproject.bramble.api.system.Clock;
 import org.briarproject.bramble.api.system.LocationUtils;
 import org.briarproject.bramble.api.system.ResourceProvider;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.plugin.bluetooth.AndroidBluetoothPluginFactory;
 import org.briarproject.bramble.plugin.tcp.AndroidLanTcpPluginFactory;
 import org.briarproject.bramble.plugin.tor.AndroidTorPluginFactory;
@@ -55,7 +55,6 @@ import java.util.Collection;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.inject.Inject;
 import javax.inject.Singleton;
@@ -125,14 +124,19 @@ public class AppModule {
 
 	@Provides
 	PluginConfig providePluginConfig(@IoExecutor Executor ioExecutor,
-			@Scheduler ScheduledExecutorService scheduler,
-			AndroidExecutor androidExecutor, SecureRandom random,
-			SocketFactory torSocketFactory, BackoffFactory backoffFactory,
-			Application app, NetworkManager networkManager,
-			LocationUtils locationUtils, EventBus eventBus,
+			TaskScheduler scheduler,
+			AndroidExecutor androidExecutor,
+			SecureRandom random,
+			SocketFactory torSocketFactory,
+			BackoffFactory backoffFactory,
+			Application app,
+			NetworkManager networkManager,
+			LocationUtils locationUtils,
+			EventBus eventBus,
 			ResourceProvider resourceProvider,
 			CircumventionProvider circumventionProvider,
-			BatteryManager batteryManager, Clock clock,
+			BatteryManager batteryManager,
+			Clock clock,
 			TimeoutMonitor timeoutMonitor) {
 		Context appContext = app.getApplicationContext();
 		DuplexPluginFactory bluetooth = new AndroidBluetoothPluginFactory(

briar-core/src/main/java/org/briarproject/briar/feed/FeedManagerImpl.java

@@ -29,7 +29,7 @@ import org.briarproject.bramble.api.plugin.event.TransportInactiveEvent;
 import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.system.Clock;
-import org.briarproject.bramble.api.system.Scheduler;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.util.StringUtils;
 import org.briarproject.briar.api.blog.Blog;
 import org.briarproject.briar.api.blog.BlogManager;
@@ -48,7 +48,6 @@ import java.util.Comparator;
 import java.util.Date;
 import java.util.List;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.logging.Logger;
 
@@ -85,7 +84,7 @@ class FeedManagerImpl implements FeedManager, EventListener, OpenDatabaseHook,
 
 	private static final int CONNECT_TIMEOUT = 60 * 1000; // Milliseconds
 
-	private final ScheduledExecutorService scheduler;
+	private final TaskScheduler scheduler;
 	private final Executor ioExecutor;
 	private final DatabaseComponent db;
 	private final ContactGroupFactory contactGroupFactory;
@@ -101,13 +100,17 @@ class FeedManagerImpl implements FeedManager, EventListener, OpenDatabaseHook,
 	private volatile boolean torActive = false;
 
 	@Inject
-	FeedManagerImpl(@Scheduler ScheduledExecutorService scheduler,
-			@IoExecutor Executor ioExecutor, DatabaseComponent db,
-			ContactGroupFactory contactGroupFactory, ClientHelper clientHelper,
-			BlogManager blogManager, BlogPostFactory blogPostFactory,
-			FeedFactory feedFactory, SocketFactory torSocketFactory,
-			Clock clock, Dns noDnsLookups) {
-
+	FeedManagerImpl(TaskScheduler scheduler,
+			@IoExecutor Executor ioExecutor,
+			DatabaseComponent db,
+			ContactGroupFactory contactGroupFactory,
+			ClientHelper clientHelper,
+			BlogManager blogManager,
+			BlogPostFactory blogPostFactory,
+			FeedFactory feedFactory,
+			SocketFactory torSocketFactory,
+			Clock clock,
+			Dns noDnsLookups) {
 		this.scheduler = scheduler;
 		this.ioExecutor = ioExecutor;
 		this.db = db;
@@ -285,7 +288,7 @@ class FeedManagerImpl implements FeedManager, EventListener, OpenDatabaseHook,
 	 * This method is called periodically from a background service.
 	 * It fetches all available feeds and posts new entries to the respective
 	 * blog.
-	 *
+	 * <p>
 	 * We can not do this within one database {@link Transaction},
 	 * because fetching can take a long time
 	 * and we can not block the database that long.
@@ -491,9 +494,9 @@ class FeedManagerImpl implements FeedManager, EventListener, OpenDatabaseHook,
 	private Comparator<SyndEntry> getEntryComparator() {
 		return (e1, e2) -> {
 			Date d1 = e1.getPublishedDate() != null ? e1.getPublishedDate() :
-							e1.getUpdatedDate();
+					e1.getUpdatedDate();
 			Date d2 = e2.getPublishedDate() != null ? e2.getPublishedDate() :
-							e2.getUpdatedDate();
+					e2.getUpdatedDate();
 			if (d1 == null && d2 == null) return 0;
 			if (d1 == null) return -1;
 			if (d2 == null) return 1;

briar-core/src/test/java/org/briarproject/briar/feed/FeedManagerImplTest.java

@@ -15,6 +15,7 @@ import org.briarproject.bramble.api.sync.Group;
 import org.briarproject.bramble.api.sync.GroupId;
 import org.briarproject.bramble.api.sync.Message;
 import org.briarproject.bramble.api.system.Clock;
+import org.briarproject.bramble.api.system.TaskScheduler;
 import org.briarproject.bramble.test.BrambleMockTestCase;
 import org.briarproject.bramble.test.ImmediateExecutor;
 import org.briarproject.briar.api.blog.Blog;
@@ -30,7 +31,6 @@ import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
 import java.util.concurrent.Executor;
-import java.util.concurrent.ScheduledExecutorService;
 
 import javax.net.SocketFactory;
 
@@ -45,8 +45,7 @@ import static org.briarproject.briar.api.feed.FeedManager.MAJOR_VERSION;
 
 public class FeedManagerImplTest extends BrambleMockTestCase {
 
-	private final ScheduledExecutorService scheduler =
-			context.mock(ScheduledExecutorService.class);
+	private final TaskScheduler scheduler = context.mock(TaskScheduler.class);
 	private final Executor ioExecutor = new ImmediateExecutor();
 	private final DatabaseComponent db = context.mock(DatabaseComponent.class);
 	private final ContactGroupFactory contactGroupFactory =
@@ -92,7 +91,7 @@ public class FeedManagerImplTest extends BrambleMockTestCase {
 
 	@Test
 	public void testFetchFeedsIoException() throws Exception {
-		BdfDictionary feedDict= new BdfDictionary();
+		BdfDictionary feedDict = new BdfDictionary();
 		BdfList feedList = BdfList.of(feedDict);
 
 		expectGetFeeds(feedList);