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