The document discusses various threading mechanisms in Android: the UI thread, loopers and handlers, async tasks, intent services, executors, executor services, and callables/futures. It explains that the UI thread manages interactions with UI widgets and should not perform long operations. Other mechanisms like async tasks, intent services, executors, and callables allow offloading work to background threads to avoid blocking the UI.

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2. Threading
Muhammad Mateen| Android Mentor

3. Threading
Topics covered in the presentation
• UI Thread
• Loppers & Handlers
• Async Tasks
• Intent Services
• Executor
• Executor Service
• Callables & Futures
Muhammad Mateen| Android Mentor

4. Threading
UI Thread
• When an application is launched, the System creates a Thread
of execution called the Main Thread or the UI Thread.
• Called the UI Thread because it is this thread which interacts
with the UI widgets.
• Don’t execute tasks that take more then 5 seconds? Why ?
Muhammad Mateen| Android Mentor

5. Threading
UI Thread
•Things to remember
• No long operations
• Don’t interact other threads with UI thread
•The UI thread runs as a NORMAL PRIORITY thread.
Muhammad Mateen| Android Mentor

6. Threading
UI Thread
•UI Thread acts as a Pipeline Thread, similar to those from Swing or
any other UI Framework
•Each action is feed into a Pipeline, and processed
•Any long operation can starve other tasks in the queue
•We can use HANDLERS to interact with this queue
Muhammad Mateen| Android Mentor

7. Threading
Loopers and Handlers
•Ordinary thread to Pipeline thread
•Loopers implements the loop
•Handler feeds the task into Queue associated with the Thread
•Together, multi-threaded processes can be handled
•Handlers detect the Looper, implicitly
•Each Handler is always tied to one Looper
Muhammad Mateen| Android Mentor

8. Threading
Async Tasks
•Easiest way to offload onto a separate thread.
• Executes task off the UI thread and post result on UI
• Not used for long processes (why ? )
• Works parallel (for less 4.x)
• Tied with Activity
• On memory shortage, it likely to be killed
Muhammad Mateen| Android Mentor

9. Threading
Async Tasks
• Why should be take care of point 3 ?
• Well for one the API documentation says so
• Secondly the Resource Queue is created by the System
• Avoid straining resources that you did not allocate
Muhammad Mateen| Android Mentor

10. Threading
Async Tasks
Methods
• onPreExecute()
• doInBackground()
• onProgressUpdate()
• onPostExecute()
Muhammad Mateen| Android Mentor

11. Threading
Intent Service
• Subclass of Service Class
• Work Queue Process
• Runs off the UI Thread
• Can place long process in onHandleIntent()
• Manages Worker Thread itself.
• Can get a out-of-the-box-queue
• Broadcast intents
Muhammad Mateen| Android Mentor

12. Threading
Executor
• Pool of runnable tasks
• Decouples the mechanics of a Task Submission from the process
of how they will be executed.
•We use this instead of creating Threads separately.
Muhammad Mateen| Android Mentor

13. Threading
Executor Service
• Add lifecycle methods to Executor
• Create N number of thread pool
• Or Executors.newSingleThreadExecutor() for a Single runnable
pool
• shut down a executor will reject new Tasks
Muhammad Mateen| Android Mentor

14. Threading
Executor Service
•Methods
shutDown() – don’t kill the running tasks
shutDownNow() – kill the running tasks
• Unused ExecutorService can be shutdown, to claim for its
resources
•Upon termination, an executor has no tasks actively executing,
no tasks awaiting execution, and no new tasks can be submitted
Muhammad Mateen| Android Mentor

15. Threading
Callables And Futures
•Biggest Issue with Runnable ?
•Callable return values after completion
• Submitting callable to executor returns a Future
• Futures can be used to check Callable’s status
•Use the get method to retrieve the result of a Future
Muhammad Mateen| Android Mentor