Android Concurrency Presentation

Android Concurrencyand background processing

Karol Depka Pradzinski Senior Android Developer at Oblong

Meetup topic vote results

Strict mode@Overridepublic void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); try { new Socket("localhost", 999); } catch (IOException e) { throw new RuntimeException(e); } }

Strict mode

Caused by: android.os.NetworkOnMainThreadException at android.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1144) at java.net.InetAddress.lookupHostByName(InetAddress.java:385) at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236) at java.net.InetAddress.getAllByName(InetAddress.java:214) at java.net.Socket.tryAllAddresses(Socket.java:108) at java.net.Socket.<init>(Socket.java:177) at java.net.Socket.<init>(Socket.java:149) at com.oblong.example.ExampleActivity.onCreate(ExampleActivity.java:19) at android.app.Activity.performCreate(Activity.java:5372)

Strict mode

Abstraction layersHigher-Level Utility Libraries Universal Image Loader

Library, Volley, …

Android Concurrency Utils AsyncTask, Loader, Handler, Service, …

Java Concurrency Utilsjava.util.concurrent … ThreadPoolExecutor, BlockingQueue, …

Java Concurrency Primitives Object monitors, “synchronized”, volatile, …











AsyncTaskpublic class MyAsyncTask extends AsyncTask<String, String, String> { @Override protected void onPreExecute() { super.onPreExecute(); // Do stuff on UI thread } @Override protected String doInBackground(String... params) { // Do stuff on BACKGROUND thread. // Caveat: usually you need exactly one param, but params[0] is not very elegant/robust this.publishProgress("Progress"); return "Result"; } @Override protected void onProgressUpdate(String... values) { super.onProgressUpdate(values); // Do stuff on UI thread } @Override protected void onPostExecute(String s) { super.onPostExecute(s); // Do stuff on UI thread } @Override protected void onCancelled() { super.onCancelled(); // Do stuff on UI thread } @Override protected void onCancelled(String s) { super.onCancelled(s); // Do stuff on UI thread } }

AsyncTask

MyAsyncTask myAsyncTask = new MyAsyncTask(); myAsyncTask.execute("Param"); // OrmyAsyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR); // OrExecutorService executor = Executors.newFixedThreadPool(4); myAsyncTask.executeOnExecutor(executor);

AsyncTask

MyAsyncTask myAsyncTask = new MyAsyncTask(); myAsyncTask.execute("Param"); // OrmyAsyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, "Param" /* too easy to forget :-] */); // OrExecutorService executor = Executors.newFixedThreadPool(4); myAsyncTask.executeOnExecutor(executor, "Param" /* too easy to forget :-] */ );

No args - Void

Pitfall: var-args - allowing accidental no-args inexecute(Params…)

public class MyAsyncTask extends AsyncTask<Void, String, String> {

private final String mandatoryParam; public MyAsyncTask(String mandatorySingleParam) { this.mandatoryParam = mandatorySingleParam; } // ...

AsyncTask

AsyncTask threadingVersion Default execution

behaviour

October 2008: Android 1.0 single “single background thread”

September 2009: Android 1.6DONUT

multi“pool of threads allowing

multiple tasks to operate in parallel”

February 2011: Android 3.0HONEYCOMB

single+

executeOnExecutor()

“tasks are executed on a single thread to avoid

common application errors caused by parallel

execution”

Posting to UI thread// Call from other thread:Runnable runnable = new Runnable() { @Override public void run() { // do stuff on UI thread } }; activity.runOnUiThread(runnable); // Or:new Handler(Looper.getMainLooper()).post(runnable);

public final void runOnUiThread(Runnable action) { if (Thread.currentThread() != mUiThread) { mHandler.post(action); } else { action.run(); // Execute immediately } }

Handler, Looper, HandlerThread

HandlerThread ht = new HandlerThread("MyHandlerThread"); ht.start(); Handler h = new Handler(ht.getLooper()); Handler handler = new Handler(ht.getLooper()){ @Override public void handleMessage(Message msg) { //.... } }; h.sendMessage(new MyMessage("MessageParam")); h.post(new Runnable() { @Override public void run() { // do stuff on the handler thread } }); // Alternatives: postAtFrontOfQueue(), postAtTime(), postDelayed()

Loader, CursorLoader

• Loads data in the background

• Reacts to changes

• Survives configuration changes

• Topic for another presentation ;-)






java.util.concurrent

• Queues: ArrayBlockingQueue, …

• Locks: Lock, ReentrantLock, …

• Atomic: AtomicInteger, AtomicLong, …

• Executor, ThreadPoolExecutor

• CountDownLatch

BlockingQueue

Throws exception Special value Blocks Times out

Insert add(e) offer(e) put(e) offer(e, time, unit)

Remove remove() poll() take() poll(time, unit)

Examine element() peek() not applicable not applicable

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#add(E)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#offer(E)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#put(E)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#offer(E,%20long,%20java.util.concurrent.TimeUnit)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#remove(java.lang.Object)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#poll(long,%20java.util.concurrent.TimeUnit)

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#take()

https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/BlockingQueue.html#poll(long,%20java.util.concurrent.TimeUnit)

https://docs.oracle.com/javase/7/docs/api/java/util/Queue.html#element()

https://docs.oracle.com/javase/7/docs/api/java/util/Queue.html#peek()

“Java Concurrency in Practice”

@ThreadSafe @Immutable @GuardedBy @NotThreadSafe






Higher-Level Utility Libraries Universal Image Loader Library, Volley, …




Linux threading primitives

By the way, we are hiringSenior Android Developer position

Oblong Industries Inc. Barcelona Office

Android Concurrency Presentation

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