Every Java developer knows that multithreading is the root of all evil and it is quite hard to write correct code for concurrent environment. But what tasks do exist in real commercial development except running code in asynchronous way? In this talk I will present several tasks from my real projects and solutions we designed for them. This talk is very application oriented and allows participants to extend their vision of concurrent programming.

1. Concurrency
in practice
Mikalai Alimenkou
http://xpinjection.com
@xpinjection

3. Disclaimer
This is all my
personal experience

4. You could follow my slides
http://slidesha.re/1vCS9dx

5. Lets start from practical tasks!

7. #1. Graceful shutdown
SERVICE 1 SERVICE 2
DB
async jobs
long batch
operations

8. Shared boolean flag

9. #2. Retry on error task

10. Configurable retry until done

11. #3. Concurrent task executor
TASK EXECUTOR
SERVICE
add task
wait for tasks completion

12. Submit tasks in single thread

13. Limit concurrent tasks

14. Wait for single or all tasks

15. Get results and reduce count

16. #4. Resource locking
RESOURCE A
THREAD 1
THREAD 2
WAIT
THREAD 3 RESOURCE B

17. Simple map to store locks

18. Count lock usages to remove it

19. Reduce synchronization penalty

20. #5. Inter-process named locks
RESOURCE
THREAD 1
THREAD 2
THREAD 3
WAIT WAIT
PROCESS 1 PROCESS 2

21. Locks are stored in simple map

22. On error throw own exception

23. #6. Limit resource access rate
RESOURCE
THREAD 1
THREAD 2
WAIT
THREAD 1
THREAD 2
3 REQ/SEC

24. Use Semaphore as limiter

25. Work with current semaphore

26. Reset not used semaphores

27. #7. Transparent batching
TASK EXECUTOR
THREAD 1
add task
wait for results
THREAD 2
THREAD 3
wait for results
add task
add task
wait for results

28. Just add task to task executor

29. Tasks processed in batches

30. Wait for first item opening batch

31. Take full batch for processing

32. #8. Resource access control
RESOURCE A
THREAD 1
THREAD 2
ALLOW
FORBID
ALLOW
THREAD 3 RESOURCE B

33. Check if resource access allowed

34. Access success is based on time

35. Check for successful access

36. #9. Sharded quick counters

37. LongAdder algorithm

38. Lets review useful tools!

39. #1. Thread factory builder

40. #2. ConcurrentUtils

41. #3. TimedSemaphore

42. #4. TimeLimiter

43. #5. RateLimiter

44. #6. Striped

45. #7. ListenableFuture

46. #8. Uninterruptibles

47. #9. CLHQueueLock

48. Spin lock implementation

49. #10. Disruptor

50. #11. ZooKeeper + Curator
• Elections
• Locks
• Barriers
• Counters
• Caches
• Nodes
• Queues

51. Useful links
• https://code.google.com/p/guava-libraries/
• http://commons.apache.org/proper/commons-lang/
• http://dou.ua/lenta/articles/clh-lock/
• http://habrahabr.ru/company/luxoft/blog/157273/
• http://habrahabr.ru/post/130113/
• http://lmax-exchange.github.io/disruptor/
• http://zookeeper.apache.org/
• http://curator.apache.org/
• http://en.wikipedia.org/wiki/Ctrie
• https://code.google.com/p/guava-libraries/wiki/ListenableFutureExplained
• https://guava-libraries.googlecode.com/files/guava-concurrent-slides.pdf

52. And remember…

53. @xpinjection
http://xpinjection.com
mikalai.alimenkou@xpinjection.com