Bài chia sẻ của anh Trần Vũ Tất Bình tại hội thảo Vietnam Mobile Day 2013 tổ chức tại TP.Hồ Chí Minh vào ngày 18/05/2013.

1. Tran Vu Tat Binh

2. I’ve done all kind of micro-optimizations, use good
algorithms, choose the right data structures but still
got serious performance issues in my mobile apps.
Our online game took about 10
minutes to download 25 MB resources
using 3G in the old version

3. Performance issues?
 The overall application runs slow.
 The application makes other
applications on phone run slower (yes, it
can)
 Users feel the application slow.
 Be strict: it’s also performance issue if
we can do much better but we don’t

4. Some interesting points
 Number of threads
 Organizing threads
 Multi-threading and network
 Mobile network under the hood

5. Number of threads
 Using too many threads
After launch Rush hour

6. Number of threads
 Using too many threads:
 Overhead
 Hard to control
 Less time for each thread
 Concurrency

7. Number of threads
 Using too few threads:
 Not take advantage of system resources
 Not so responsive

8. Number of threads
So how many?
Flexible and should not be a fixed
number, see the next “Organizing
threads” for more details.

9. Organizing threads
 Usually, there are 3 kinds of task
 Blocking UI task
 Updater task
 Lazy media task

10. Organizing threads
 Blocking UI task
○ When there are no other data
on screen
○ When user definitely have to
wait for updated data only
Should be a single thread with
high priority since user can not
proceed if task is not done.

11. Organizing threads
 Updater task
○ Updating / refreshing
○ Loading more
○ User can still interact with
existed data on screen
○ Can move to other screen
without finishing task
Should be a thread pool
(suggest size 2-4)

12. Organizing threads
 Lazy media task
○ Thumbnails for existed data
○ A list/grid of images
Should be 2 thread pools: one
for downloading and one for
decoding

13. Organizing threads
 Lazy media task (con.)
 Usually most heavy task  focus optimizing
 Why separating into downloading and
decoding
○ Images might be in local cache already and
decoding usually much faster than
downloading, so don’t let downloading slow
down the progress
○ Decoding pool size should be based on CPU
cores
○ Downloading pool size should be based on
network status

14. Organizing threads
 Decoding pool size
NUMBER_OF_CORES = Runtime.getRuntime().availableProcessors();
mDecodeThreadPool = new ThreadPoolExecutor(NUMBER_OF_CORES,
NUMBER_OF_CORES, KEEP_ALIVE_TIME, KEEP_ALIVE_TIME_UNIT,
mDecodeWorkQueue);

15. Organizing threads
 Downloading pool size
 Normal:
○ Fixed size (may be 8 like in some tutorials)
 More optimized:
○ 2G – size 4
○ 3G – size 8
○ 4G – size 16 (or more)
○ WIFI – size 8
 Much more optimized:
○ Based on network speed, increasing size if
can still download faster, decreasing size if
still not slower, until get the best size.

16. Organizing threads
 Why variable size is better choice:
2G pool size 2
2G pool size 4
2G pool size 8

17. Organizing threads
 Why variable size is better choice:
3G pool size 4 3G pool size 8
3G pool size 24

18. Organizing threads
 Facts:
 Each connection has a limited bandwidth
 The phone’s network connection has a
overall limited bandwidth
 There are network latency causing “gaps”
while downloading

19. Organizing threads
 Downloading pool size
 Too small size
○ Waste network bandwidth
○ Drain battery life if using mobile network
○ Slow
 Too large size
○ Take more time to show individual image (not
overall images on screen)  users feel slow
○ TCP congestion control
○ Slower to start downloading new images when
scrolling
Variable size based on network status is good
choice but need more time to implement

20. Organizing threads
 Conclusion:
 Blocking UI task – 1 thread
 Updater task – 1 thread pool size 2 - 4
 Lazy media task – 2 thread pools
○ 1 thread pool for decoding size = available cores
○ 1 thread pool for downloading size based on
network status

21. Mobile network under the hood
 Online applications like messenger,
news reader, social app or online
game… some got serious issues when
using mobile network
○ Battery drain
○ Slow response

22. Mobile network
 Typical 3G wireless radio state machine (source)

23. Mobile network
 Messenger application
○ Small data message
○ Transferring more
frequently
○ No fixed schedule

24. Mobile network
 Online game
○ Small data message
○ Transferring much more
frequently
○ Usually fixed schedule
○ Responsiveness is
importance

25. Mobile network
 Social app
 News reader
 Photo sharing
 Music app
…

26. Mobile network
 Optimize data to transfer (as always)
 Batch operation
 Prefetch
 When receive, if need to transmit then
do quick
 If possible, do at the same time with
other apps

27. Q&A

28. Thank you!