"Preallocate objects, so we won't count gc time."
n := 1000000.
objects := Array new: n streamContents: [ :stream |
       n timesRepeat: [ stream nextPut: Object new ] ].

set := IdentitySet new: n.

Smalltalk garbageCollect.
[1 to: n do: [ :i | set add: (objects at: i) ] ] timeToRun. "4949"

set := LargeIdentitySet new.
Smalltalk garbageCollect.
[1 to: n do: [ :i | set add: (objects at: i) ] ] timeToRun. "331"

set := (PluggableSet new: n)
       hashBlock: [ :object | object identityHash * 4096 + object class identityHash * 64 ]; "Change this to #basicIdentityHash in Pharo"
       equalBlock: [ :a :b | a == b ];
       yourself.
Smalltalk garbageCollect.
[1 to: n do: [ :i | set add: (objects at: i) ] ] timeToRun. "5511"


I also have a LargeIdentityDictionary, which is relatively fast, but not as fast as LargeIdentitySet, because (for some unknown reason) we don't have a primitive that could support it. If we had a primitive like primitive 132 which would return the index of the element if found or 0 if not, then we could have a really fast LargeIdentityDictionary.

Levente

Cheers,
Henry