SLIDE 1
Linked Weak Reference Arrays
A Hybrid Approach to Efficient Bulk Finalization
Andrés Valloud
IWST 2015
Weak arrays
ivars
Linked Weak Reference Arrays A Hybrid Approach to Efficient Bulk - - PowerPoint PPT Presentation
Linked Weak Reference Arrays A Hybrid Approach to Efficient Bulk - - PowerPoint PPT Presentation
Linked Weak Reference Arrays A Hybrid Approach to Efficient Bulk Finalization Andrs Valloud IWST 2015 Weak arrays ivars Weak arrays ivars Weak arrays mourn ivars 0 Ephemerons key Ephemerons key Ephemerons mourn key
SLIDE 2
SLIDE 3
Weak arrays
ivars
SLIDE 4
Weak arrays
ivars
mourn
SLIDE 5
Ephemerons
key
SLIDE 6
Ephemerons
key
SLIDE 7
Ephemerons
key
mourn
SLIDE 8
GemStone/S
Server Image GS Client
SLIDE 9
GemStone/S
Server Image Ephemerons
SLIDE 10
GemStone/S
Server Image Weak arrays
SLIDE 11
Observation overhead
Ephemerons Weak arrays Evaluation Space required per client
- bject
at least one extra
- bject header
negligible weak arrays much more compact VM cost per client object
- ne extra
finalization queue slot negligible weak arrays much more efficient in bulk Finalization cost per client
- bject
ephemerons finalized only as needed scanning for tombstones weak arrays induce linear search
SLIDE 12
No scanning, deployed
Begin interaction End interaction
SLIDE 13
No scanning, deployed
Begin interaction End interaction
SLIDE 14
No scanning, deployed
Begin interaction End interaction
H E N C E N O T O M B S T O N E S S T R O N G C O P Y
SLIDE 15
No scanning, deployed
Begin interaction End interaction
O R I G I N A L L Y W E A K S T R O N G A T T H I S T I M E W E A K O N C E A G A I N
isWeakContainer: false isWeakContainer: true
SLIDE 16
No scanning, proposed
Begin mourning End mourning WeakArray>>mourn 1 to: self size do: [:eachIndex | (self at: eachIndex) == 0 ifTrue: [self mournAt: eachIndex] ]
SLIDE 17
No scanning, proposed
Begin mourning End mourning
6 12 15
LinkedWeakArray
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No scanning, proposed
Begin mourning End mourning
6 12 15
LinkedWeakArray>>mourn | nextIndex | nextIndex := self firstTombstoneIndex. "6" [nextIndex == 0] whileFalse: [ self mournAt: nextIndex. nextIndex := self at: nextIndex "12, 15, 0" ]
SLIDE 19
No scanning, proposed
Begin GC End mourning
O R I G I N A L L Y W E A K S T R O N G A T T H I S T I M E W E A K O N C E A G A I N
setWeakContainer(false); isWeakContainer: true VM queues for finalization LinkedWeakArray>>mourn
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Mourning performance I
Quotient
0.0 0.6 1.3 1.9 2.6 3.2 3.9 4.5 5.2 5.8 6.5 7.1 7.8 8.4 9.1 9.7 10.4 11.0
Tombstoning rates
1 2 3 5 7 10
SLIDE 21
Tombstoning rates
2^8 2^20
Linked weak array sizes
2^4 2^14
SLIDE 22