Amrit Sanjeev talks about how AsyncTask works internally and how you can tweak it to work it better or understand it better

1. Async is not as simple as we think
DEEP DIVE INTO
ANDROID ASYNCTASK
Amrit Sanjeev
Bangalore Android User Group

2. Agenda
• About me
• Blrdroid GDG
• Some of my thoughts
• Q&A

3. About me
• Organizer, Bangalore Android User Group
( www.blrdroid.org )
• Staff engineer for Mobile at Digital Insight (formerly
Intuit)
• Previous companies – Philips research, IBM.
• Active in the local developer community
• Mentor at 10,000 startups (www.10000startups.com)
• Part of Intel Influencer program

4. Bangalore Android User Group ( www.BlrDroid.org)
• Largest open Android developer community in the India
• Over 5100+ members
• 4.5 years and completely free.
• 53 meet-ups
• 5 hackathons
• Blrdroid teach – College edition more than 2400+ students from over
35 colleges participated.
• Active participation in events like Droidcon, Global Android
Developer hackathon, Google Bizdroid etc

5. How threading in android works
most general principles apply well here too

6. Processes and threads
• Android system starts a new Linux process for the
application with a single thread of execution
• All components of the same application run in the
same process and thread (called the "main"
thread)
• you can arrange for different components in
your application to run in separate processes, and
you can create additional threads for any process.

7. Processes
android:process attribute that can specify a process
in which that component should run
Android tries to shut processes before activities
when it wants memory.
A process is started again for those components
when there's again work for them to do.
Use this when you want to isolate component
execution from each other .

8. Process ranking and priority

9. Threads – General guidelines
Do not block
the UI thread
Do not access
the Android
UI toolkit from
outside the UI
thread

10. Threads types
• Main
– important because it is in charge of dispatching
events to the appropriate user interface.
– also the thread in which your application interacts
with components from the Android UI toolkit
• Worker threads
– operations to perform that are not instantaneous
– code can get complicated

11. Here’s where AsyncTask comes
Just the basics

12. What is an Asynctask
Android implements a single thread model
Abstract class provided to help UI Thread
properly
Perform long operation in background
without locking the UI thread

13. Steps
• doInBackground: Code performing long running
operation goes in this method.
• onPostExecute: This method is called after
doInBackground method completes processing. Result from
doInBackground is passed to this method.
• onPreExecute: This method is called before
doInBackground method is called.
• onProgressUpdate: This method is invoked by calling
publishProgress anytime from doInBackground call this
method.

14. Pros and cons
Pros
• easy to use
• android specific
• easy UI-
interaction
Cons
• Different
behavior in
different
versions of
android

15. Deep dive into Asynctask
its more complicated than it seems

16. Quick question
How many of you are confident implementing
concurrent code in java ??

17. Changes over time
Before Donut
• All tasks execute serially.
• Before a task can execute, all the previous tasks have to be finished
• Bad throughput
From Donut to
GingerBread
• Each task was executed on a separate thread
• Concurrency issues
Honeycomb
and onwards
• Execution was switched back to the sequential implementation
• executeOnExecutor(Executor) was added if parallel execution was
needed.
• SERIAL_EXECUTOR & THREAD_POOL_EXECUTOR

18. Standard coding pattern – Concurrent execution
public class ConcurrentAsyncTask {
public static void execute(AsyncTask asyncTask) {
if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.HONEYCOMB_MR1) {
asyncTask.execute();
} else {
asyncTask.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR);
}
}
}

19. Cancelling a task
A task can be cancelled at any time by invoking cancel().
Invoking this method will cause subsequent calls to isCancelled() to
return true.
After invoking this method, onCancelled(), instead of onPostExecute()
will be invoked after doInBackground() returns.
To ensure that a task is cancelled as quickly as possible, you should always
check the return value of isCancelled() periodically from doInBackground()