Ensure that observers see the final state even if they're added late.

bramble-api/src/main/java/org/briarproject/bramble/api/plugin/file/RemovableDriveTask.java

@@ -1,6 +1,6 @@
 package org.briarproject.bramble.api.plugin.file;
 
-import org.briarproject.bramble.api.event.EventExecutor;
+import org.briarproject.bramble.api.Consumer;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 
 import java.io.File;
@@ -14,21 +14,43 @@ public interface RemovableDriveTask extends Runnable {
 	File getFile();
 
 	/**
-	 * Adds an observer to the task.
+	 * Adds an observer to the task. The observer will be notified of state
+	 * changes on the event thread. If the task has already finished, the
+	 * observer will be notified of its final state.
 	 */
-	void addObserver(Observer o);
+	void addObserver(Consumer<State> observer);
 
 	/**
 	 * Removes an observer from the task.
 	 */
-	void removeObserver(Observer o);
+	void removeObserver(Consumer<State> observer);
 
-	interface Observer {
+	class State {
 
-		@EventExecutor
-		void onProgress(long done, long total);
+		private final long done, total;
+		private final boolean finished, success;
 
-		@EventExecutor
-		void onCompletion(boolean success);
+		public State(long done, long total, boolean finished, boolean success) {
+			this.done = done;
+			this.total = total;
+			this.finished = finished;
+			this.success = success;
+		}
+
+		public long getDone() {
+			return done;
+		}
+
+		public long getTotal() {
+			return total;
+		}
+
+		public boolean isFinished() {
+			return finished;
+		}
+
+		public boolean isSuccess() {
+			return success;
+		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveReaderTask.java

@@ -45,10 +45,10 @@ class RemovableDriveReaderTask extends RemovableDriveTaskImpl
 		if (r == null) {
 			LOG.warning("Failed to create reader");
 			registry.removeReader(contactId, this);
-			visitObservers(o -> o.onCompletion(false));
+			setSuccess(false);
 			return;
 		}
-		progressTotal.set(file.length());
+		setTotal(file.length());
 		eventBus.addListener(this);
 		connectionManager.manageIncomingConnection(ID, new DecoratedReader(r));
 	}
@@ -59,7 +59,7 @@ class RemovableDriveReaderTask extends RemovableDriveTaskImpl
 			MessageAddedEvent m = (MessageAddedEvent) e;
 			if (contactId.equals(m.getContactId())) {
 				LOG.info("Message received");
-				updateProgress(m.getMessage().getRawLength());
+				addDone(m.getMessage().getRawLength());
 			}
 		}
 	}
@@ -83,7 +83,7 @@ class RemovableDriveReaderTask extends RemovableDriveTaskImpl
 			delegate.dispose(exception, recognised);
 			registry.removeReader(contactId, RemovableDriveReaderTask.this);
 			eventBus.removeListener(RemovableDriveReaderTask.this);
-			visitObservers(o -> o.onCompletion(!exception && recognised));
+			setSuccess(!exception && recognised);
 		}
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveTaskImpl.java

@@ -11,11 +11,11 @@ import org.briarproject.bramble.api.plugin.simplex.SimplexPlugin;
 import org.briarproject.bramble.api.properties.TransportProperties;
 
 import java.io.File;
+import java.util.ArrayList;
 import java.util.List;
-import java.util.concurrent.CopyOnWriteArrayList;
 import java.util.concurrent.Executor;
-import java.util.concurrent.atomic.AtomicLong;
 
+import javax.annotation.concurrent.GuardedBy;
 import javax.annotation.concurrent.ThreadSafe;
 
 import static java.lang.Math.min;
@@ -34,9 +34,12 @@ abstract class RemovableDriveTaskImpl implements RemovableDriveTask {
 	final RemovableDriveTaskRegistry registry;
 	final ContactId contactId;
 	final File file;
-	private final List<Observer> observers = new CopyOnWriteArrayList<>();
-	final AtomicLong progressTotal = new AtomicLong(0);
-	private final AtomicLong progressDone = new AtomicLong(0);
+
+	private final Object lock = new Object();
+	@GuardedBy("lock")
+	private final List<Consumer<State>> observers = new ArrayList<>();
+	@GuardedBy("lock")
+	private State state = new State(0, 0, false, false);
 
 	RemovableDriveTaskImpl(
 			Executor eventExecutor,
@@ -61,19 +64,22 @@ abstract class RemovableDriveTaskImpl implements RemovableDriveTask {
 	}
 
 	@Override
-	public void addObserver(Observer o) {
-		observers.add(o);
+	public void addObserver(Consumer<State> o) {
+		State state;
+		synchronized (lock) {
+			observers.add(o);
+			state = this.state;
+		}
+		if (state.isFinished()) {
+			eventExecutor.execute(() -> o.accept(state));
+		}
 	}
 
 	@Override
-	public void removeObserver(Observer o) {
-		observers.remove(o);
-	}
-
-	void visitObservers(Consumer<Observer> visitor) {
-		eventExecutor.execute(() -> {
-			for (Observer o : observers) visitor.accept(o);
-		});
+	public void removeObserver(Consumer<State> o) {
+		synchronized (lock) {
+			observers.remove(o);
+		}
 	}
 
 	SimplexPlugin getPlugin() {
@@ -86,9 +92,37 @@ abstract class RemovableDriveTaskImpl implements RemovableDriveTask {
 		return p;
 	}
 
-	void updateProgress(long progress) {
-		long done = progressDone.addAndGet(progress);
-		long total = progressTotal.get();
-		visitObservers(o -> o.onProgress(min(done, total), total));
+	void setTotal(long total) {
+		synchronized (lock) {
+			state = new State(state.getDone(), total, state.isFinished(),
+					state.isSuccess());
+			notifyObservers();
+		}
+	}
+
+	void addDone(long done) {
+		synchronized (lock) {
+			// Done and total come from different sources; make them consistent
+			done = min(state.getDone() + done, state.getTotal());
+			state = new State(done, state.getTotal(), state.isFinished(),
+					state.isSuccess());
+		}
+		notifyObservers();
+	}
+
+	void setSuccess(boolean success) {
+		synchronized (lock) {
+			state = new State(state.getDone(), state.getTotal(), true, success);
+		}
+		notifyObservers();
+	}
+
+	@GuardedBy("lock")
+	private void notifyObservers() {
+		List<Consumer<State>> observers = new ArrayList<>(this.observers);
+		State state = this.state;
+		eventExecutor.execute(() -> {
+			for (Consumer<State> o : observers) o.accept(state);
+		});
 	}
 }

bramble-core/src/main/java/org/briarproject/bramble/plugin/file/RemovableDriveWriterTask.java

@@ -51,7 +51,7 @@ class RemovableDriveWriterTask extends RemovableDriveTaskImpl
 		if (w == null) {
 			LOG.warning("Failed to create writer");
 			registry.removeWriter(contactId, this);
-			visitObservers(o -> o.onCompletion(false));
+			setSuccess(false);
 			return;
 		}
 		// TODO: Get total bytes to send from DB
@@ -101,7 +101,7 @@ class RemovableDriveWriterTask extends RemovableDriveTaskImpl
 			delegate.dispose(exception);
 			registry.removeWriter(contactId, RemovableDriveWriterTask.this);
 			eventBus.removeListener(RemovableDriveWriterTask.this);
-			visitObservers(o -> o.onCompletion(!exception));
+			setSuccess(!exception);
 		}
 	}
 }

bramble-core/src/test/java/org/briarproject/bramble/plugin/file/RemovableDriveIntegrationTest.java

@@ -11,7 +11,6 @@ import org.briarproject.bramble.api.identity.IdentityManager;
 import org.briarproject.bramble.api.lifecycle.LifecycleManager;
 import org.briarproject.bramble.api.nullsafety.NotNullByDefault;
 import org.briarproject.bramble.api.plugin.file.RemovableDriveTask;
-import org.briarproject.bramble.api.plugin.file.RemovableDriveTask.Observer;
 import org.briarproject.bramble.api.sync.event.MessageStateChangedEvent;
 import org.briarproject.bramble.test.BrambleTestCase;
 import org.briarproject.bramble.test.TestDatabaseConfigModule;
@@ -100,15 +99,8 @@ public class RemovableDriveIntegrationTest extends BrambleTestCase {
 		RemovableDriveTask reader = device.getRemovableDriveManager()
 				.startReaderTask(contactId, file);
 		CountDownLatch disposedLatch = new CountDownLatch(1);
-		reader.addObserver(new Observer() {
-			@Override
-			public void onProgress(long done, long total) {
-			}
-
-			@Override
-			public void onCompletion(boolean success) {
-				disposedLatch.countDown();
-			}
+		reader.addObserver(state -> {
+			if (state.isFinished()) disposedLatch.countDown();
 		});
 		// Wait for the messages to be delivered
 		assertTrue(listener.delivered.await(TIMEOUT_MS, MILLISECONDS));
@@ -125,15 +117,8 @@ public class RemovableDriveIntegrationTest extends BrambleTestCase {
 		RemovableDriveTask writer = device.getRemovableDriveManager()
 				.startWriterTask(contactId, file);
 		CountDownLatch disposedLatch = new CountDownLatch(1);
-		writer.addObserver(new Observer() {
-			@Override
-			public void onProgress(long done, long total) {
-			}
-
-			@Override
-			public void onCompletion(boolean success) {
-				disposedLatch.countDown();
-			}
+		writer.addObserver(state -> {
+			if (state.isFinished()) disposedLatch.countDown();
 		});
 		// Wait for the writer to be disposed
 		disposedLatch.await(TIMEOUT_MS, MILLISECONDS);