1. Mobile Computing
Dr. Mohsin Ali Memon

2. Threads • Basic approach
- Make a task list with Executors.newFixedThreadPool
- Add tasks to list with taskList.execute(someRunnable)
• Three variations on the theme
- Separate classes that implement Runnable
- Main Activity implements Runnable
- Inner classes that implement Runnable
- Race conditions and synchronization
• Related topics
- Helpful Thread-related methods

3. Motivation for Concurrent Programming
• Pros
- Advantages even on single-processor systems
• Efficiency
- Downloading image files
• Convenience
- A clock icon
• Responsiveness
- If you block the main thread, event handlers will not respond
- Some devices have multiple cpus or cores
• Find out via Runtime.getRuntime().availableProcessors()
• Cons
- Significantly harder to debug and maintain than single-
threaded apps

4. Steps for Concurrent Programming

5. Steps for Concurrent Programming cont’d

6. Approach One: Separate Classes that Implement Runnable

7. Separate Runnable Class: Template Code
This code should not update the UI. If you need to update UI, use AsyncTask class.

8. Thread Mechanism One: Example

9. Thread Mechanism One: Example con’d

10. Helper Class

11. Thread Mechanism One: Example Result

12. Pros and Cons of Approach

13. Approach Two: Main App Implements Runnable

14. Main App Implements Runnable: Template Code

15. Thread Mechanism Two: Example

16. Thread Mechanism Two: Results

17. Pros and Cons of Approach

18. Approach Three: Inner Class that Implements Runnable

19. Inner Class implements Runnable: Template code

20. Thread Mechanism Three: Example

21. Thread Mechanism Three: Example cont’d

22. Thread Mechanism Three: Example Result

23. Pros and cons of approach

24. Summary

25. Race Condition

26. Race Conditions: Example

27. Race Conditions: Example cont’d

28. Race Conditions: Result

29. Race Conditions: Solution

30. Race Conditions: Solution

31. Helpful –Thread related Methods

32. Methods in ExecutorService Class

33. Threads Cannot Update UI

34. Updating UI All at Once

35. Displaying a network image

36. BitmapUtils: Getting a Bitmap

37. Making a View for an Image

38. BitmapUtils:Getting a view for image

39. Example: Unthreaded Image Viewer

40. Activity

41. Results

42. Updating UI with View.post

43. Example: Multithreaded Image Viewer

44. Main Activity

45. Main Activity Button Handler

46. Main Activity: Runnable Inner Class (For Background)

47. Main Activity: Runnable Inner Class (For UI Thread)

48. Results

49. Downloading Images via AsyncTask