Use fixed resources for sending

Introduce 2 limits on the resources used.

Use an Executor with a thread pool of max size 1 for sending HTTP requests
to Sentry. This thread pool will use 0 threads at idle, and reduce the
number of threads in use down to 0 after a minute of no exceptions.

Use a fixed queue for events. A queue of up to 50 events will be queued
for sending to Sentry. If more than 50 events are queued, the new events
will be discarded.

These two changes will add a fixed ceiling to the amount of resources the
Sentry client will use on the device.

Author: Marc O'Morain

sentry-android/src/main/java/com/joshdholtz/sentry/Sentry.java

@@ -39,6 +39,12 @@
 import java.util.Map;
 import java.util.TimeZone;
 import java.util.UUID;
+import java.util.concurrent.ArrayBlockingQueue;
+import java.util.concurrent.Executor;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.ThreadPoolExecutor;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicLong;
 
 import javax.net.ssl.SSLContext;
 import javax.net.ssl.TrustManager;
@@ -72,11 +78,7 @@
 import android.net.ConnectivityManager;
 import android.net.NetworkInfo;
 import android.net.Uri;
-import android.os.AsyncTask;
 import android.os.Build;
-import android.os.Handler;
-import android.os.HandlerThread;
-import android.os.Looper;
 import android.util.DisplayMetrics;
 import android.util.Log;
 import android.view.WindowManager;
@@ -96,8 +98,10 @@ public class Sentry {
 	private int verifySsl;
 	private SentryEventCaptureListener captureListener;
 	private JSONObject contexts = new JSONObject();
+	private Executor executor;
 
 	private static final String TAG = "Sentry";
+	private static final int MAX_QUEUE_LENGTH = 50;
 
 	private Sentry() {
 	}
@@ -134,11 +138,31 @@ public static void init(Context context, String dsn, boolean setupUncaughtExcept
 		Sentry.getInstance().packageInfo = findPackage(Sentry.getInstance().context);
 		Sentry.getInstance().verifySsl = getVerifySsl(dsn);
 		Sentry.getInstance().contexts = readContexts(Sentry.getInstance().context, Sentry.getInstance().packageInfo);
+		Sentry.getInstance().executor = fixedQueueDiscardingExecutor(MAX_QUEUE_LENGTH);
 
 		if (setupUncaughtExceptionHandler) {
 			Sentry.getInstance().setupUncaughtExceptionHandler();
 		}
 	}
+
+	private static Executor fixedQueueDiscardingExecutor(int queueSize) {
+		// Name our threads so that it is easy for app developers to see who is creating threads.
+		final ThreadFactory threadFactory = new ThreadFactory() {
+			private final AtomicLong count = new AtomicLong();
+			@Override
+			public Thread newThread(Runnable runnable) {
+				final Thread thread = new Thread(runnable);
+				thread.setName(String.format(Locale.US, "Sentry HTTP Thread %d", count.incrementAndGet()));
+				return thread;
+			}
+		};
+
+		return new ThreadPoolExecutor(
+				0, 1, // Keep 0 threads alive. Max pool size is 1.
+				60, TimeUnit.SECONDS, // Kill unused threads after this length.
+				new ArrayBlockingQueue<Runnable>(queueSize),
+				threadFactory, new ThreadPoolExecutor.DiscardPolicy()); // Discard exceptions
+	}
 
 	private static int getVerifySsl(String dsn) {
 		int verifySsl = 1;
@@ -319,24 +343,7 @@ public static void captureEvent(SentryEventBuilder builder) {
 
 		log("Request - " + request.getRequestData());
 
-		// Check if on main thread - if not, run on main thread
-		if (Looper.myLooper() == Looper.getMainLooper()) {
-			doCaptureEventPost(request);
-		} else if (Sentry.getInstance().context != null) {
-
-			HandlerThread thread = new HandlerThread("SentryThread") {};
-			thread.start();
-			Runnable runnable = new Runnable() {
-				@Override
-				public void run() {
-					doCaptureEventPost(request);
-				}
-			};
-			Handler h = new Handler(thread.getLooper());
-			h.post(runnable);
-
-		}
-
+		doCaptureEventPost(request);
 	}
 
 	private static boolean shouldAttemptPost() {
@@ -425,11 +432,10 @@ private static void doCaptureEventPost(final SentryEventRequest request) {
 			InternalStorage.getInstance().addRequest(request);
 			return;
 		}
-		
-		new AsyncTask<Void, Void, Void>(){
-			@Override
-			protected Void doInBackground(Void... params) {
 
+		getInstance().executor.execute(new Runnable() {
+			@Override
+			public void run() {
 				int projectId = Integer.parseInt(getProjectId());
 				String url = Sentry.getInstance().baseUrl + "/api/" + projectId + "/store/";
 
@@ -501,11 +507,9 @@ protected Void doInBackground(Void... params) {
 				} else {
 					InternalStorage.getInstance().addRequest(request);
 				}
-
-				return null;
 			}
 
-			private byte[] readBytes(InputStream inputStream) throws IOException { 
+			private byte[] readBytes(InputStream inputStream) throws IOException {
 				// this dynamically extends to take the bytes you read
 				ByteArrayOutputStream byteBuffer = new ByteArrayOutputStream();
 
@@ -523,7 +527,7 @@ private byte[] readBytes(InputStream inputStream) throws IOException {
 				return byteBuffer.toByteArray();
 			}
 
-		}.execute();
+		});
 
 	}