6장 Thread Synchronization

1. Java Performance artdb@ex-em.com | performeister.tistory.com | twitter @novathinker Thread Synchronization

2. Java Performance 2 artdb@ex-em.com | performeister.tistory.com | twitter @novathinker Thread Synchronization 1) Java Thread 2) Thread Synchronization 3) Cooperation 4) Mutual execution 5) Light-Weight Lock Hotspot Synchronization 1) Light-Weight Lock 2) Biased Locking IBM JVM Synchronization 1) Thin Lock 2) Lock Reservation

3. Java Performance artdb@ex-em.com | performeister.tistory.com | twitter @novathinker Thread Synchnonization

4. Java Performance 4 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Java Thread – Green Thread • JVM Created, scheduling Thread • 1.1 JVM Thread model • OS Thread n:1 • OS Thread • CPU – Native Thread • OS Kernel Thread • 1.3 Default

5. Java Performance 5 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Thread Synchronization – Monitor : Java Synchronization Mechanism – Monitor • Cooperation – Class object wait(),notify() – Thread • Mutual Exclusion – Class class –

6. Java Performance 6 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Cooperation – Cooperation • wait() Reader Thread Buffer empty Listen notify() Thread Buffer full

7. Java Performance 7 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Cooperation – Monitor Monitor Critical Section Monitor suspend

8. Java Performance 8 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Cooperation – Monitor

9. Java Performance 9 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Mutual Exclusion – Shared Data • Runtime Data Area Data Thread • Heap  Instance Variables • Method Area  Class Variables • Object Class Monitor lock • Mutex object lock • Object Lock – Thread Object

10. Java Performance 10 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Mutual Exclusion – Object Lock • Class ﬁle java.lang.class instance • Object lock object(instance) locking • Thread object locking • object lock counter – Lock count – Lock count – Count = 0 thread lock • Thread Critical Section lock

11. Java Performance 11 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Mutual Exclusion – Critical Section • Critical Section – Synchronized statement – Synchronized method • Critical section object reference • Critical section instruction thread object lock • Critical section lock release • Object Lock critical section JVM

12. Java Performance 12 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Thread Synchronization • Light-Weight Lock – light-weight lock • JVM Light-Weight Lock • Object OS Mutex heavyweight lock • locking No Atomic Operation Enter, Exit monitor Contended Heavy-Weight OS Lock Yes

13. Java Performance artdb@ex-em.com | performeister.tistory.com | twitter @novathinker Hotspot Synchronization

14. Java Performance 14 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Light-Weight Lock – Object Header • Object Header word Mark Work Mark Word Hash Code (0) Age Biased Tag Thread ID, epoch(1) 23 bit 6 bit 1 bit 2 bit Hash Code (0) Age Biased Tag Biased bit Tag Thread ID, epoch(1) 0 01 Unlocked (000) Lock Record Address 0 00 Light-weight locked (010) Monitor Address 0 10 Heavy-weight locked 0 11 Marked for GC (011) Forwarding Address 1 01 Biased / Biasable

15. Java Performance 15 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Light-Weight Lock – Light-Weight Locking • Object Header word Mark Work • Atomic compare-and-swap(CAS) instruction lock • CAS thread lock • CAS heavy weight lock • Object lock thread stack frame mark word move (displaced mark ) • Lock Mark Word

16. Java Performance 16 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Light-Weight Lock – Light-Weight Locking Execution Execution Stack Stack Locking Method Method Activation Activation Mark word 01 Stack pointer Lock Displaced hdr Mark word 01 Record Object Object owner owner

17. Java Performance 17 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Light-Weight Lock – Light-Weight Locking Unlock Hash Code Age 0 01 Recursive lock Light weight lock Pointer to lock record 00 Unlock heavy weight lock Pointer to heavyweight 10

18. Java Performance 18 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Light-Weight Lock – Light-Weight Locking • Atomic Operation multiprocessor • lock Thread locking • Thread Lock • Thread lock –

19. Java Performance 19 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Biased Locking – Java 6 default • Java 5 update 6 – Light Weight lock • Object lock thread lock • CAS – Biased lock • lock CAS • Thread (biased) lock CAS

20. Java Performance 20 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Biased Locking Object Allocate Bias enabled Bias disabled Unlock Unlock 0 epoch Age 1 01 Hash Code Age 0 01 Recursive lock Initial lock Rebias Revoke bias Pointer to lock record 00 locked Thread ID epoch Age 1 01 Pointer to heavyweight monitor 10 Lock / Unlock

21. Java Performance 21 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Biased Locking – Biased lock • Mark word tag 1 • 101  biased or biasable (thread id 0 unlocked) – Bias revocation • Lock Thread Thread lock light weight lock • Owner thread bias • Object mark word – Thread suspend  expensive

22. Java Performance 22 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Biased Locking – Bulk Revocation • Class revocation • Class instance bias invalid – Bulk Rebiasing • Thread lock class • class instance bias invalid

23. Java Performance 23 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com Hotspot Synchronization • Biased Locking – Option • -XX:+UseBiasedLocking (Java5 update 6~) : biased lock java 6 default • -XX:BiasedLockingStartupDelay=0 (Java6~) : JVM Delay second • -XX:+TraceBiasedLocking (Java6~) : Biased Lock Debugging

24. Java Performance artdb@ex-em.com | performeister.tistory.com | twitter @novathinker IBM JVM Synchronization

25. Java Performance 25 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com IBM JVM Synchronization • Thin Lock – Thin lock Fat lock • Fat Lock : heavy-weight locking system • Thin Lock : Light-weight locking system – Object lock – Recursive lock • Lock default thin • Lock • IBM JDK 1.1.2

26. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 26 • Thin Lock – Object Layout for Thin Lock • Lock Word Garbage Collection (2bits) bit (2bits) Pinned Object Size G P (double word) Array bit (1bit) Class pointer or array size Monitor Shape bit Thread index count (1bit) S H T A Monitor index Type Hash code state (2bits) Object Data Hash code

27. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com27 • Thin Lock – Object Layout for Thin Lock • Object Lock Word 24 bit • Lock Word bit Lock – Monitor Shape Lock – 0  Thin lock – 1  Fat lock • Thin Lock •Recursive (nested) lock count •Maximum 255 nested lock Count 0 Thread ID (15 bits) (8bits)

28. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 28 • Thin Lock Spin – Thin Locking lock loop Fail Own No Get CAS Lock? Lock? No Success YES YES 0 Nested Lock Lock 24bit monitor shape, Count count 0 Lock Release Fat lock Thread ID Monitor index monitor Count Lock Release index Lock word CAS Monitor shape 1

29. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 29 • Lock Reservation – Java 5 – Atomic Operation • 75% Lock thread • Performance – Idea • Object Lock (reserve) cost

30. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 30 • Lock Reservation – Object Layout • Object Header Lock Word • LRV bit : Lock reserved –1 Reserved –0 locking System LRV bit Thread ID Recursion Cnt* 1 (deﬁned by base locking algorithm) 0

31. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 31 • Lock Reservation – Reserved mode • Reserve Thread ID • Recursion Count Lock Acquisition Thread ID 0 1 Reserved, Released Thread ID >0 1 Reserved , 0 0 1 Reserved

32. Java Performance Java Performance Fundamental | twitter @novathinker IBM JVM Synchronization artdb@ex-em.com | performeister.tistory.com 32 • Lock Reservation – Locking • Reserved mode atomic operation Recursion count • Thread Reservation cancel unreserve 0 0 1 Thread ID 0 1 aaaaaa 0 acquire release acquire unreserve Thread ID 1 1 bbbbbb 0 acquire release unreserve Thread ID 2 1 ccccccc 0 Reserved Mode Base Mode

33. Java Performance 33 Java Performance Fundamental | twitter @novathinker artdb@ex-em.com | performeister.tistory.com

6장 Thread Synchronization

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6장 Thread Synchronization