Use AndroidExecutor for background tasks that make API calls.

briar-android/src/org/briarproject/system/AndroidExecutorImpl.java

@@ -1,46 +1,59 @@
 package org.briarproject.system;
 
-import android.app.Application;
-import android.content.Context;
 import android.os.Handler;
 import android.os.Looper;
-import android.os.Message;
 
 import org.briarproject.android.api.AndroidExecutor;
 
 import java.util.concurrent.Callable;
+import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Future;
 import java.util.concurrent.FutureTask;
+import java.util.concurrent.RejectedExecutionException;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+import javax.inject.Inject;
 
 class AndroidExecutorImpl implements AndroidExecutor {
 
-	private final Handler handler;
+	private final Runnable loop;
+	private final AtomicBoolean started = new AtomicBoolean(false);
+	private final CountDownLatch startLatch = new CountDownLatch(1);
 
-	AndroidExecutorImpl(Application app) {
-		Context ctx = app.getApplicationContext();
-		handler = new FutureTaskHandler(ctx.getMainLooper());
+	private volatile Handler handler = null;
+
+	@Inject
+	AndroidExecutorImpl() {
+		loop = new Runnable() {
+			public void run() {
+				Looper.prepare();
+				handler = new Handler();
+				startLatch.countDown();
+				Looper.loop();
+			}
+		};
+	}
+
+	private void startIfNecessary() {
+		if (started.getAndSet(true)) return;
+		Thread t = new Thread(loop, "AndroidExecutor");
+		t.setDaemon(true);
+		t.start();
+		try {
+			startLatch.await();
+		} catch (InterruptedException e) {
+			throw new RejectedExecutionException(e);
+		}
 	}
 
 	public <V> Future<V> submit(Callable<V> c) {
-		Future<V> f = new FutureTask<V>(c);
-		handler.sendMessage(Message.obtain(handler, 0, f));
+		FutureTask<V> f = new FutureTask<>(c);
+		execute(f);
 		return f;
 	}
 
 	public void execute(Runnable r) {
+		startIfNecessary();
 		handler.post(r);
 	}
-
-	private static class FutureTaskHandler extends Handler {
-
-		private FutureTaskHandler(Looper looper) {
-			super(looper);
-		}
-
-		@Override
-		public void handleMessage(Message m) {
-			((FutureTask<?>) m.obj).run();
-		}
-	}
 }
-