Share a single OS wake lock among all holders.

bramble-android/src/main/java/org/briarproject/bramble/api/system/AndroidWakeLockFactory.java

@@ -1,16 +1,9 @@
 package org.briarproject.bramble.api.system;
 
-import android.os.PowerManager;
-
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 @NotNullByDefault
 public interface AndroidWakeLockFactory {
 
-	/**
-	 * Creates and returns a wake lock.
-	 *
-	 * @param levelAndFlags See {@link PowerManager#newWakeLock(int, String)}
-	 */
-	AndroidWakeLock createWakeLock(int levelAndFlags);
+	AndroidWakeLock createWakeLock();
 }

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

@@ -13,7 +13,6 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 
-import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
 import static org.briarproject.bramble.api.plugin.BluetoothConstants.PROP_ADDRESS;
 import static org.briarproject.bramble.util.AndroidUtils.isValidBluetoothAddress;
 
@@ -36,7 +35,7 @@ class AndroidBluetoothTransportConnection
 		this.socket = socket;
 		in = timeoutMonitor.createTimeoutInputStream(
 				socket.getInputStream(), plugin.getMaxIdleTime() * 2);
-		wakeLock = wakeLockFactory.createWakeLock(PARTIAL_WAKE_LOCK);
+		wakeLock = wakeLockFactory.createWakeLock();
 		wakeLock.acquire();
 		String address = socket.getRemoteDevice().getAddress();
 		if (isValidBluetoothAddress(address)) remote.put(PROP_ADDRESS, address);

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

@@ -23,7 +23,6 @@ import java.util.concurrent.Executor;
 import javax.net.SocketFactory;
 
 import static android.content.Context.MODE_PRIVATE;
-import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
 
 @MethodsNotNullByDefault
 @ParametersNotNullByDefault
@@ -54,7 +53,7 @@ class AndroidTorPlugin extends TorPlugin {
 				maxLatency, maxIdleTime,
 				appContext.getDir("tor", MODE_PRIVATE));
 		this.appContext = appContext;
-		wakeLock = wakeLockFactory.createWakeLock(PARTIAL_WAKE_LOCK);
+		wakeLock = wakeLockFactory.createWakeLock();
 	}
 
 	@Override

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidWakeLockFactoryImpl.java

@@ -15,6 +15,7 @@ import javax.annotation.concurrent.Immutable;
 import javax.inject.Inject;
 
 import static android.content.Context.POWER_SERVICE;
+import static android.os.PowerManager.PARTIAL_WAKE_LOCK;
 import static java.util.concurrent.TimeUnit.MINUTES;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
@@ -34,22 +35,20 @@ class AndroidWakeLockFactoryImpl implements AndroidWakeLockFactory {
 	 */
 	private static final long SAFETY_MARGIN_MS = SECONDS.toMillis(10);
 
-	private final TaskScheduler scheduler;
-	private final PowerManager powerManager;
-	private final String tag;
+	private final SharedWakeLock sharedWakeLock;
 
 	@Inject
 	AndroidWakeLockFactoryImpl(TaskScheduler scheduler, Application app) {
-		this.scheduler = scheduler;
-		powerManager = (PowerManager)
+		PowerManager powerManager = (PowerManager)
 				requireNonNull(app.getSystemService(POWER_SERVICE));
-		tag = getWakeLockTag(app);
+		String tag = getWakeLockTag(app);
+		sharedWakeLock = new RenewableWakeLock(powerManager, scheduler,
+				PARTIAL_WAKE_LOCK, tag, LOCK_DURATION_MS, SAFETY_MARGIN_MS);
 	}
 
 	@Override
-	public AndroidWakeLock createWakeLock(int levelAndFlags) {
-		return new RenewableWakeLock(powerManager, scheduler, levelAndFlags,
-				tag, LOCK_DURATION_MS, SAFETY_MARGIN_MS);
+	public AndroidWakeLock createWakeLock() {
+		return new AndroidWakeLockImpl(sharedWakeLock);
 	}
 
 	private String getWakeLockTag(Context ctx) {

bramble-android/src/main/java/org/briarproject/bramble/system/AndroidWakeLockImpl.java

@@ -0,0 +1,46 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+
+import javax.annotation.concurrent.GuardedBy;
+import javax.annotation.concurrent.ThreadSafe;
+
+/**
+ * A wrapper around a {@link SharedWakeLock} that provides the more convenient
+ * semantics of {@link AndroidWakeLock} (i.e. calls to acquire() and release()
+ * don't need to be balanced).
+ */
+@ThreadSafe
+@NotNullByDefault
+class AndroidWakeLockImpl implements AndroidWakeLock {
+
+	private final SharedWakeLock sharedWakeLock;
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private boolean held = false;
+
+	AndroidWakeLockImpl(SharedWakeLock sharedWakeLock) {
+		this.sharedWakeLock = sharedWakeLock;
+	}
+
+	@Override
+	public void acquire() {
+		synchronized (lock) {
+			if (!held) {
+				held = true;
+				sharedWakeLock.acquire();
+			}
+		}
+	}
+
+	@Override
+	public void release() {
+		synchronized (lock) {
+			if (held) {
+				held = false;
+				sharedWakeLock.release();
+			}
+		}
+	}
+}

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

@@ -4,22 +4,23 @@ import android.os.PowerManager;
 import android.os.PowerManager.WakeLock;
 
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
-import org.briarproject.bramble.api.system.AndroidWakeLock;
 import org.briarproject.bramble.api.system.TaskScheduler;
 
 import java.util.concurrent.Future;
 import java.util.logging.Logger;
 
 import javax.annotation.Nullable;
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.util.concurrent.TimeUnit.MILLISECONDS;
 import static java.util.logging.Level.INFO;
 import static java.util.logging.Logger.getLogger;
+import static org.briarproject.bramble.api.nullsafety.NullSafety.requireNonNull;
 
 @ThreadSafe
 @NotNullByDefault
-class RenewableWakeLock implements AndroidWakeLock {
+class RenewableWakeLock implements SharedWakeLock {
 
 	private static final Logger LOG =
 			getLogger(RenewableWakeLock.class.getName());
@@ -31,10 +32,14 @@ class RenewableWakeLock implements AndroidWakeLock {
 	private final long durationMs, safetyMarginMs;
 
 	private final Object lock = new Object();
+	@GuardedBy("lock")
 	@Nullable
-	private WakeLock wakeLock; // Locking: lock
+	private WakeLock wakeLock;
+	@GuardedBy("lock")
 	@Nullable
-	private Future<?> future; // Locking: lock
+	private Future<?> future;
+	@GuardedBy("lock")
+	private int refCount = 0;
 
 	RenewableWakeLock(PowerManager powerManager, TaskScheduler scheduler,
 			int levelAndFlags, String tag, long durationMs,
@@ -49,16 +54,21 @@ class RenewableWakeLock implements AndroidWakeLock {
 
 	@Override
 	public void acquire() {
-		if (LOG.isLoggable(INFO)) LOG.info("Acquiring wake lock " + tag);
 		synchronized (lock) {
-			if (wakeLock != null) {
-				LOG.info("Already acquired");
-				return;
+			refCount++;
+			if (refCount == 1) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info("Acquiring wake lock " + tag);
+				}
+				wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
+				// We do our own reference counting so we can replace the lock
+				// TODO: Check whether using a ref-counted wake lock affects
+				//  power management apps
+				wakeLock.setReferenceCounted(false);
+				wakeLock.acquire(durationMs + safetyMarginMs);
+				future = scheduler.schedule(this::renew, durationMs,
+						MILLISECONDS);
 			}
-			wakeLock = powerManager.newWakeLock(levelAndFlags, tag);
-			wakeLock.setReferenceCounted(false);
-			wakeLock.acquire(durationMs + safetyMarginMs);
-			future = scheduler.schedule(this::renew, durationMs, MILLISECONDS);
 		}
 	}
 
@@ -80,17 +90,17 @@ class RenewableWakeLock implements AndroidWakeLock {
 
 	@Override
 	public void release() {
-		if (LOG.isLoggable(INFO)) LOG.info("Releasing wake lock " + tag);
 		synchronized (lock) {
-			if (wakeLock == null) {
-				LOG.info("Already released");
-				return;
+			refCount--;
+			if (refCount == 0) {
+				if (LOG.isLoggable(INFO)) {
+					LOG.info("Releasing wake lock " + tag);
+				}
+				requireNonNull(future).cancel(false);
+				future = null;
+				requireNonNull(wakeLock).release();
+				wakeLock = null;
 			}
-			if (future == null) throw new AssertionError();
-			future.cancel(false);
-			future = null;
-			wakeLock.release();
-			wakeLock = null;
 		}
 	}
 }

bramble-android/src/main/java/org/briarproject/bramble/system/SharedWakeLock.java

@@ -0,0 +1,22 @@
+package org.briarproject.bramble.system;
+
+import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
+import org.briarproject.bramble.api.system.AndroidWakeLock;
+
+@NotNullByDefault
+interface SharedWakeLock {
+
+	/**
+	 * Acquires the wake lock. This increments the wake lock's reference count,
+	 * so unlike {@link AndroidWakeLock#acquire()} every call to this method
+	 * must be followed by a balancing call to {@link #release()}.
+	 */
+	void acquire();
+
+	/**
+	 * Releases the wake lock. This decrements the wake lock's reference count,
+	 * so unlike {@link AndroidWakeLock#release()} every call to this method
+	 * must follow a balancing call to {@link #acquire()}.
+	 */
+	void release();
+}