Memory Nitpicks and Tidbits

Presentation from the Android meetup held on 19.4.2016 @Five.

Transcript

1. Memory tidbits and nitpicks 19.4.2016. @FIVE #android Tomislav Novoselec
2. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
3. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
4. Memory constraints • Low end devices are still widely used • Memory is shared across all the applications - be a good citizen!
5. Why are memory operations so expensive? • Allocation • Concurrent collection • Collection for allocation
6. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
13. Impact on your heap • More allocations mean larger heap • Larger heap means less memory for everything else • Task manager will kill greedy apps
14. Talk is cheap, show me the code!
15. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
16. int vs Integer • int takes only 4 bytes • Integer takes at least 16 bytes (even more on different JVM-s and architectures)
17. - “But I need null value to tell me that something was not found” Anonymous developer
18. - ”But I need to use them in some kind of collection” Another anonymous developer
19. Sparse collections to the rescue! - No need for boxing/autoboxing - Approximately same performance but smaller memory footprint - Suitable for smaller number of items in collection
20. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
21. Avoid allocations in inner loop
22. @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Rect outRect = new Rect(); outRect.set(0, 0, canvas.getWidth()/2, canvas.getHeight()/2); Paint blue = new Paint(); blue.setColor(Color.BLUE); blue.setStyle(Paint.Style.FILL); canvas.drawRect(outRect, blue); }
23. Reuse objects
24. View.java /** * <p>Computes the coordinates of this view on the screen. The argument * must be an array of two integers. After the method returns, the array * contains the x and y location in that order.</p> * * @param location an array of two integers in which to hold the coordinates */ public void getLocationOnScreen(@Size(2) int[] location) { getLocationInWindow(location); final AttachInfo info = mAttachInfo; if (info != null) { location[0] += info.mWindowLeft; location[1] += info.mWindowTop; } }
25. int[] startingLocation = new int[2]; listItem.getLocationOnScreen(startingLocation); this.containerTop = startingLocation[1]; this.containerHeight = listItem.getHeight(); orderId.getLocationOnScreen(startingLocation); this.idTop = startingLocation[1]; this.idLeft = startingLocation[0]; clientName.getLocationOnScreen(startingLocation); this.clientNameTop = startingLocation[1]; this.clientNameLeft = startingLocation[0]; time.getLocationOnScreen(startingLocation); this.timeTop = startingLocation[1]; this.timeLeft = startingLocation[0];
26. • Object caches • Object pools Reuse objects II
27. Content • Memory constraints • Garbage collector • Primitives vs object types • Avoiding allocations • Beware the language • Q&A
28. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
29. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
30. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
31. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
32. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
33. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
34. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
35. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
36. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
37. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
38. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
39. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
40. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
41. Trashing memory with ArrayList public List<String> names(List<User> users) { List<String> names = new ArrayList<>(users.size()); for (User user : users) { names.add(user.name); } return unmodifiableList(names); }
42. Enhanced foreach loop int[] arrayOfNumbers = getArrayOfNumbers(); for (int number : arrayOfNumbers){ // Body } List<Integer> listOfNumbers = getListOfNumbers(); for (Integer number : listOfNumbers){ // Body }
43. After compilation for (int i = 0; i < arrayOfNumbers.length; i++) { int number = arrayOfNumbers[i]; // Body } for (Iterator<Integer> iter = listOfNumbers.iterator(); iter.hasNext(); ) { Integer number = iter.next(); // Body }
44. Better? public void numbers(List<Integer> listOfNumbers) { for (int i = 0, size = listOfNumbers.size(); i < size; i++) { Integer number = listOfNumbers.get(i); // Body } }
45. Conclusion • Memory is precious, be thoughtful of how you use it • Garbage collector is your best friend, and your worst enemy • Saving memory bit by bit could improve your app’s performance
46. Q&A
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