Ouch! bad bug! I don't know if we need the speed, but we need the correctness.

To add to weirdness, I tested that (Object canUnderstand: Object methodDictionary size) is true, but I have (Object canUnderstand: Object selectors size) answering false, because it has two non nil slot less than the tally...

2013/10/25 Eliot Miranda eliot.miranda@gmail.com

Hi All,

I just got a little burned.  I was searching through an Array of

symbols and integers (it is the PrimitiveTable from the VM), wanting to filter-out methods with a with a certain pragma. The code looks like:

anArray doWithIndex: [:entry :index| (self whichClassIncludesSelector: entry) ifNotNil: [:c| | m | m := c >> entry. (m pragmaAt: #option:) ifNotNil: [:pragma| (initializationOptions at: (pragma arguments first) ifAbsent: [true]) ifFalse: [anArray at: index put: 0]]]]

the error was a keyNotFound error for c >> entry. Turns out entry was the integer 306, a code for a quick primitive that returns some inst var. The question is why did (self whichClassIncludesSelector: entry) evaluate to other than nil given that 306 is /not/ a selector in any of the classes from self on up. Well, it's MethodDictionary's use of pointsTo: that is at fault:

MethodDictionary>>includesKey: aSymbol "This override assumes that pointsTo is a fast primitive"

aSymbol ifNil: [^ false]. ^ self pointsTo: aSymbol

ProtoObject>>pointsTo: anObject "This method returns true if self contains a pointer to anObject, and returns false otherwise" <primitive: 132> 1 to: self class instSize do: [:i | (self instVarAt: i) == anObject ifTrue: [^ true]]. 1 to: self basicSize do: [:i | (self basicAt: i) == anObject ifTrue: [^ true]]. ^ false

Turns out that 306 was the tally of one of the method dictionaries along self's superclass chain. This seems to be to be completely bogus. Do we really need crude performance hacks like this any more? -- best, Eliot

On Fri, Oct 25, 2013 at 02:18:07PM -0700, Eliot Miranda wrote:

ProtoObject>>pointsTo: anObject "This method returns true if self contains a pointer to anObject, and returns false otherwise" <primitive: 132> 1 to: self class instSize do: [:i | (self instVarAt: i) == anObject ifTrue: [^ true]]. 1 to: self basicSize do: [:i | (self basicAt: i) == anObject ifTrue: [^ true]]. ^ false

The version of ProtoObject>>pointsTo: that you quote here has a time stamp from 1999. The current version in Squeak has a time stamp of 2008, and looks like this:

ProtoObject>>pointsTo: anObject "Answers true if I hold a reference to anObject, or false otherwise. Or stated another way:

Answers true if the garbage collector would fail to collect anObject because I hold a reference to it, or false otherwise"

^ (self instVarsInclude: anObject) or: [self class == anObject]