The Inbox: Collections-nice.723.mcz

Nicolas Cellier uploaded a new version of Collections to project The Inbox:
http://source.squeak.org/inbox/Collections-nice.723.mcz

==================== Summary ====================

Name: Collections-nice.723
Author: nice
Time: 27 October 2016, 8:04:09.437881 pm
UUID: 0c01b091-06e9-694d-9415-56c62c06babc
Ancestors: Collections-nice.722

Provide a WeakIdentityDictionary - a good candidate for being used as environments undeclared pool.

=============== Diff against Collections-nice.722 ===============

Item was changed:
  ----- Method: IdentityDictionary>>keyAtValue:ifAbsent: (in category 'accessing') -----
  keyAtValue: value ifAbsent: exceptionBlock
  "Answer the key that is the external name for the argument, value. If
  there is none, answer the result of evaluating exceptionBlock."
   
+ ^self keyAtIdentityValue: value ifAbsent: exceptionBlock!
- ^super keyAtIdentityValue: value ifAbsent: exceptionBlock!

Item was added:
+ IdentityDictionary subclass: #WeakIdentityDictionary
+ instanceVariableNames: 'vacuum'
+ classVariableNames: ''
+ poolDictionaries: ''
+ category: 'Collections-Weak'!
+
+ !WeakIdentityDictionary commentStamp: 'nice 10/27/2016 20:00' prior: 0!
+ I am a WeakIdentityDictionary, that is a dictionary pointing weakly to its associations of key->value pairs.
+ I am especially usefull for handling undeclared bindings that will be naturally garbage collected without having to scan all the CompiledMethods.
+
+ Instance variables:
+     vacuum    <Object> a unique object used for marking empty slots
+
+ Due to usage of WeakArray for my own storage, reclaimed slots will be nilled out.
+ I cannot consider a nil slot as empty because of garbage collection does not fix collisions.
+ Thus I need to differentiate empty slots (vacuum) from garbaged collected slots (nil).
+
+ If I did not reclaim the nil slots and make them vacuum again, then my capacity would grow indefinitely.
+ My strategy to avoid such growth is to randomly cleanup the garbage collected slot encountered when scanning for a key.
+ It should mitigate the growth since this method is used when adding a new entry.
+
+ Due to those not yet cleaned-up nil slots I might over-estimate my size. Don't take it too literally.!

Item was added:
+ ----- Method: WeakIdentityDictionary class>>arrayType (in category 'private') -----
+ arrayType
+ ^ WeakArray!

Item was added:
+ ----- Method: WeakIdentityDictionary>>add: (in category 'accessing') -----
+ add: anAssociation
+
+ | index |
+ index := self scanFor: anAssociation key.
+ (array at: index)
+ ifNil: [ self atNewIndex: index put: anAssociation ]
+ ifNotNil: [ :element |
+ element == vacuum
+ ifTrue: [ self atNewIndex: index put: anAssociation ]
+ ifFalse: [ element value: anAssociation value ] ].
+ ^anAssociation!

Item was added:
+ ----- Method: WeakIdentityDictionary>>associationAt:ifAbsent: (in category 'accessing') -----
+ associationAt: key ifAbsent: aBlock
+ "Answer the association with the given key.
+ If key is not found, return the result of evaluating aBlock."
+
+ ^((array at: (self scanFor: key))
+ ifNil: [ aBlock value ]
+ ifNotNil: [:association |
+ association == vacuum
+ ifTrue: [ aBlock value ]
+ ifFalse: [ association ] ])!

Item was added:
+ ----- Method: WeakIdentityDictionary>>associationsDo: (in category 'enumerating') -----
+ associationsDo: aBlock
+ "Evaluate aBlock for each of the receiver's elements (key/value
+ associations)."
+
+ tally = 0 ifTrue: [ ^self].
+ 1 to: array size do: [ :index |
+ (array at: index) ifNotNil: [ :element |
+ element == vacuum ifFalse: [ aBlock value: element ] ] ]!

Item was added:
+ ----- Method: WeakIdentityDictionary>>at:ifAbsent: (in category 'accessing') -----
+ at: key ifAbsent: aBlock
+ "Answer the value associated with the key or, if key isn't found,
+ answer the result of evaluating aBlock."
+
+ ^((array at: (self scanFor: key))
+ ifNil: [ aBlock ]
+ ifNotNil: [:association |
+ association == vacuum
+ ifTrue: [ aBlock ]
+ ifFalse: [ association ] ]) value "Blocks and Associations expect #value"!

Item was added:
+ ----- Method: WeakIdentityDictionary>>at:ifPresent:ifAbsentPut: (in category 'accessing') -----
+ at: key ifPresent: oneArgBlock ifAbsentPut: absentBlock
+ "Lookup the given key in the receiver. If it is present, answer the value of
+ evaluating oneArgBlock with the value associated with the key. Otherwise
+ add the value of absentBlock under the key, and answer that value."
+
+ | index value |
+ index := self scanFor: key.
+ (array at: index) ifNotNil:
+ [:element|
+ element == vacuum ifFalse: [^oneArgBlock value: element value] ].
+ value := absentBlock value.
+ self atNewIndex: index put: (self associationClass key: key value: value).
+ ^value!

Item was added:
+ ----- Method: WeakIdentityDictionary>>at:put: (in category 'accessing') -----
+ at: key put: anObject
+ "Set the value at key to be anObject.  If key is not found, create a
+ new entry for key and set is value to anObject. Answer anObject."
+
+ | index |
+ index := self scanFor: key.
+ (array at: index)
+ ifNil:
+ ["it's possible to get here if the association just died"
+ self atNewIndex: index put: (self associationClass key: key value: anObject) ]
+ ifNotNil: [ :association |
+ association == vacuum
+ ifTrue: [ self atNewIndex: index put: (self associationClass key: key value: anObject) ]
+ ifFalse: [association value: anObject ] ].
+ ^anObject!

Item was added:
+ ----- Method: WeakIdentityDictionary>>cleanupIndex: (in category 'private') -----
+ cleanupIndex: anInteger
+ array at: anInteger put: vacuum.
+ tally := tally - 1.
+ self fixCollisionsFrom: anInteger.!

Item was added:
+ ----- Method: WeakIdentityDictionary>>fixCollisionsFrom: (in category 'private') -----
+ fixCollisionsFrom: start
+ "The element at start has been removed and replaced by vacuum.
+ This method moves forward from there, relocating any entries
+ that had been placed below due to collisions with this one."
+
+ | element index |
+ index := start.
+ [ (element := array at: (index := index \\ array size + 1)) == vacuum ] whileFalse: [
+ element
+ ifNil:
+ [ "The binding at this slot was reclaimed - finish the cleanup"
+ array at: index put: vacuum.
+ tally := tally - 1 ]
+ ifNotNil:
+ [| newIndex |
+ (newIndex := self scanWithoutGarbagingFor: element key) = index ifFalse: [
+ array
+ at: newIndex put: element;
+ at: index put: vacuum ] ] ]!

Item was added:
+ ----- Method: WeakIdentityDictionary>>growTo: (in category 'private') -----
+ growTo: anInteger
+ "Grow the elements array and reinsert the old elements"
+
+ | oldElements |
+ oldElements := array.
+ array := self class arrayType new: anInteger withAll: vacuum.
+ self noCheckNoGrowFillFrom: oldElements!

Item was added:
+ ----- Method: WeakIdentityDictionary>>includesKey: (in category 'testing') -----
+ includesKey: key
+ "Answer whether the receiver has a key equal to the argument, key."
+
+ ^(array at: (self scanFor: key))
+ ifNil:
+ ["it just has been reclaimed"
+ false]
+ ifNotNil: [:element | element ~~ vacuum]!

Item was added:
+ ----- Method: WeakIdentityDictionary>>initialize: (in category 'private') -----
+ initialize: n
+ vacuum := Object new.
+ array := self class arrayType new: n withAll: vacuum.
+ tally := 0!

Item was added:
+ ----- Method: WeakIdentityDictionary>>noCheckNoGrowFillFrom: (in category 'private') -----
+ noCheckNoGrowFillFrom: anArray
+ "Add the elements of anArray except nils to me assuming that I don't contain any of them, they are unique and I have more free space than they require."
+
+ 1 to: anArray size do: [ :index |
+ (anArray at: index) ifNotNil: [ :association |
+ association == vacuum
+ ifFalse: [array
+ at: (self scanForEmptySlotFor: association key)
+ put: association ] ] ]!

Item was added:
+ ----- Method: WeakIdentityDictionary>>postCopy (in category 'copying') -----
+ postCopy
+ "Beware: do share the bindings, so changing a binding value in the copy will also change it in the original.
+ Copying the bindings would not make sense: we hold weakly on them, so they would die at first garbage collection."
+
+ | oldVacuum |
+ super postCopy.
+ oldVacuum := vacuum.
+ vacuum := Object new.
+ array := array collect: [ :association |
+ association ifNotNil: [
+ association == oldVacuum
+ ifTrue: [ vacuum ]
+ ifFalse: [ association ] ] ]!

Item was added:
+ ----- Method: WeakIdentityDictionary>>removeKey:ifAbsent: (in category 'removing') -----
+ removeKey: key ifAbsent: aBlock
+ "Remove key (and its associated value) from the receiver. If key is not in
+ the receiver, answer the result of evaluating aBlock. Otherwise, answer
+ the value externally named by key."
+
+ | index association |
+ index := self scanFor: key.
+ (association := (array at: index)) == vacuum ifTrue: [ ^aBlock value ].
+ self cleanupIndex: index.
+ ^association value!

Item was added:
+ ----- Method: WeakIdentityDictionary>>scanFor: (in category 'private') -----
+ scanFor: anObject
+ "Scan the array for the first slot containing either
+ - a vacuum object indicating an empty slot
+ - or a binding whose key matches anObject.
+ Answer the index of that slot or raise an error if no slot is found.
+ When garbage collected slots are encountered, perform a clean-up."
+
+ | index start rescan |
+ [
+ rescan := false.
+ index := start := anObject scaledIdentityHash \\ array size + 1.
+ [
+ (array at: index)
+ ifNil:
+ ["Object at this slot has been garbage collected.
+ A rescan is necessary because fixing collisions
+ might have moved the target before current index."
+ self cleanupIndex: index.
+ rescan := true]
+ ifNotNil:
+ [:element | (element == vacuum or: [ element key == anObject ])
+ ifTrue: [ ^index ].
+ (index := index \\ array size + 1) = start ] ] whileFalse.
+ rescan ] whileTrue.
+ self errorNoFreeSpace!

Item was added:
+ ----- Method: WeakIdentityDictionary>>scanForEmptySlotFor: (in category 'private') -----
+ scanForEmptySlotFor: anObject
+ "Scan the array for the first empty slot marked by vacuum object.
+ Answer the index of that slot or raise an error if no slot is found.
+ Ignore the slots that have been garbage collected (those containing nil)."
+
+ | index start |
+ index := start := anObject scaledIdentityHash \\ array size + 1.
+ [
+ (array at: index)
+ ifNotNil:
+ [:element | element == vacuum ifTrue: [ ^index ] ].
+ (index := index \\ array size + 1) = start ] whileFalse.
+ self errorNoFreeSpace!

Item was added:
+ ----- Method: WeakIdentityDictionary>>scanWithoutGarbagingFor: (in category 'private') -----
+ scanWithoutGarbagingFor: anObject
+ "Scan the array for the first slot containing either
+ - a vacuum object indicating an empty slot
+ - or a binding whose key matches anObject.
+ Answer the index of that slot or raise an error if no slot is found.
+ Ignore the slots that have been garbage collected (those containing nil)"
+
+ | index start |
+ index := start := anObject scaledIdentityHash \\ array size + 1.
+ [
+ (array at: index)
+ ifNotNil:
+ [:element | (element == vacuum or: [ element key == anObject ])
+ ifTrue: [ ^index ] ].
+ (index := index \\ array size + 1) = start ] whileFalse.
+ self errorNoFreeSpace!

Item was changed:
+ ----- Method: WeakSet class>>arrayType (in category 'private') -----
- ----- Method: WeakSet class>>arrayType (in category 'as yet unclassified') -----
  arrayType
 
  ^WeakArray!