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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 heavy- weight 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