At JavaOne keynote this year, Mark Reinhold talked about how Java 9 was much bigger than Jigsaw. To put that in numbers - 80+ JEPs bigger! Yes, we see more presentations on Jigsaw since it brings about modularity to the once monolithic JDK. But what about those other JEPs?! One of those "other" JEPs, is JEP 143 - 'Improve Contended Locking'. Monica will apply her performance engineering approach and talk about JEP 143 and Oracle's Studio Analyzer Performance Tool. The crux of the presentation will entail comparing performance of contended locks in JDK 9 to JDK 8.

2. About Me
Java/JVM/GC performance person
Current Life:
Consultant who solves Managed Runtime performance issues
Past Life:
Worked with Oracle, Sun,AMD…
©2017 CodeKaram1

3. Agenda
• Setting the stage
• A quick glance at JDK 9 JEPs
• Building a problem statement
• Studying JEP 143 – Improve contended locking
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4. Agenda
• Quick overview of top-down and bottom-up performance
approaches
• Choosing the right approach!
• Building our arsenal!
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5. Agenda
• Observing the targeted improvements
• Demo comparing JDK 9 with JDK 8
• Summarizing the observations
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6. Setting The Stage
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7. JEPs in JDK 9
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There are 89 total JEPs in JDK 9

8. JEPs in JDK 9
…and contended locking performanceimprovement (JEP143) is
one of them J
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9. What is JEP 143?
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JEP 143 brings about improvements to contended locks*
*In the past (Java 6) we have alreadyseen improvements to uncontendedlocksusing
BiasedLockingtechnique.

10. Building A Problem
Statement
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11. Summary of JEP 143
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“Improve the performance of contended Java object monitors”

12. ©2017 CodeKaram11
“Improve the performance of contended Java object monitors”
Summary of JEP 143

13. Uncontended Locks
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A single thread ‘t’ is executing a synchronized method

14. Contended Locks
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A different thread ‘u’ wants to enter the synchronized method
that is already locked by thread ‘t’

15. Contended Locks
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This is a heavy weight lock also known as inflated lock
Object Monitor maintains “WaitSet” for threads waiting for the
contended lock

16. Java Monitors
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Wait
Q
Object
Monitor
Enter
Exit
Q

17. Wait Set
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• A set of threads
• At creation – empty set of threads
• Can be manipulated only by:
• Object.wait, Object.notify, Object.notifyAll

18. Java Monitors
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Wait
Q
Object
Monitor
Enter
Exit
Q
Wait
Notify

19. Top-Down
Performance Approach
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20. What areYouTrying to Achieve?
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Improve application?

21. Top-Down Approach
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OS
Hardware
Application Ecosystem
Application
JRE
JVM

22. Top Down Approach - Process
•Step 1Monitor
•Step 2 Profile
•Step 3Analyze
•Step 4 Tune +
Apply

23. Bottom-Up
Performance Approach
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24. What areYouTrying to Achieve?
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Improve the platform?

25. Bottom-Up Approach
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OS
Hardware
Application Ecosystem
Application
JRE
JVM

26. Bottom Up Approach - Process
•Step 1Monitor
•Step 2 Profile
•Step 3Analyze
•Step 4 Tune +
Apply

27. Choosing The Right
Approach …
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28. Improve the JVM
What AreWeTryingTo Do?
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29. The Bottom-Up
Approach
HenceWeChoose…
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30. Bottom Up Approach
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I NEED the power!!
… to stress the platform

31. Setting Up For
Benchmarking
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32. Where to Start?
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• Know what you are stressing
• Get/ write the appropriate workload/ application
• Get/write the appropriate tools

33. Know What You’re
Stressing…
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34. Speed UpTargets
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• PlatformEvent::unpark()
• Java monitor enter operations
• Java monitor exit operations
• Java monitor notify/notifyAll operations

35. Get/Write The
Appropriate
Workload/Application
…
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36. FromThe JEP …
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LockLoops-JSR166-Doug-Sept2009 (was LockLoops):
The benchmark compares multiple locking techniques
For our purpose, we just need to test the contended locks.

37. Contended Locking Test
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private static class BuiltinLockLoop extends LockLoop {
final int loop(int n) {
int sum = 0;
while (n-- > 0) {
synchronized (this) {
v = LoopHelpers.compute1(v);
}
sum += LoopHelpers.compute2(v);
}
return sum;
}
}

38. Contended Locking Test
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private static class BuiltinLockLoop extends LockLoop {
final int loop(int n) {
int sum = 0;
while (n-- > 0) {
synchronized (this) {
v = LoopHelpers.compute1(v);
}
sum += LoopHelpers.compute2(v);
}
return sum;
}
}

39. Where to Next?
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Ensure that you are in fact measuring contended object monitor
performance!

40. How DoWe DoThat?
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Bypass biased locking: Use -XX:-UseBiasedLocking
Bypass stack based locking: Use -XX:+UseHeavyMonitors

41. Get/Write The
Appropriate Tools …
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42. Oracle Developer
Studio Performance
Tool
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43. Profiling with ‘collect’
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• -j on: default for when target is Java
• -p on: default clock-profiling rate of ~100 samples/second
• -H on: heap tracing
• -t <duration>: time over which to record data
• -h <ctr_def>…: specify HW counter profiling

44. Observing The
Targeted
Improvements
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45. Speed UpTargets
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• PlatformEvent::unpark()
• Java monitor enter operations
• Java monitor exit operations
• Java monitor notify/notifyAll operations

46. Demo - Comparing
Contended Locking in
JDK 9 to JDK 8
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47. Summarizing the
Observations
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48. Speed UpTargets
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•PlatformEvent::unpark()
• Java monitor enter operations
• Java monitor exit operations
• Java monitor notify/notifyAll operations

49. ©2017 CodeKaram48
JDK 9 ExclusiveTime JDK8 ExclusiveTime Method Name
0.400 0.941 os::PlatformEvent::unpark()
Unpark

50. ImprovementTargets
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• PlatformEvent::unpark()
•Java monitor enter operations
• Java monitor exit operations
• Java monitor notify/notifyAll operations

51. ©2017 CodeKaram50
JDK 9 ExclusiveTime JDK8 ExclusiveTime Method Name
97.678 187.001 ObjectMonitor::enter(Thread*)
2.462 3.432 ObjectMonitor::EnterI(Thread*)
Monitor Enter

52. Speed UpTargets
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• PlatformEvent::unpark()
• Java monitor enter operations
•Java monitor exit operations
• Java monitor notify/notifyAll operations

53. ©2017 CodeKaram52
JDK 9 ExclusiveTime JDK8 ExclusiveTime Method Name
2.302 2.352 ObjectMonitor::exit(bool,…)
0.000 0.961 ObjectMonitor::ExitEpilog(Thread*
,…)
Monitor Exit

54. Speed UpTargets
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• PlatformEvent::unpark()
• Java monitor enter operations
• Java monitor exit operations
•Java monitor notify/notifyAll operations

55. ©2017 CodeKaram54
I’ll leave that as a take-home exercise for you all! J
Notify/ NotifyAll

56. Further Reading
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57. http://openjdk.java.net/jeps/143
https://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html
https://wiki.openjdk.java.net/display/HotSpot/Synchronization
https://blogs.oracle.com/dave/entry/biased_locking_in_hotspot
http://extremeperformance.expert
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