Hi eliot
> I repost the mail to the mailing-list since I do not see it in the vm-dev
>
> did you post to vm-dev?
yes but since I'm travelling may be the mail was lost or I could not see
appearing because one of my rules pushed it somewhere.
I changed machines and I have to get used to 10.8. My mail now decide to use
the wrong account :(
>>
>> Hi
>>
>> I was reading the following method in the VM code and I have a couple of
>> questions:
>>
>> - I do not understand why lookupMethodInClass: may return a class. I was
>> thinking that it would return a method.
>
>
> It doesn't matter what it returns as it's return value is always ignored.
Ok I will read again the code. reading Slang is still nicer than plain
generated C :)
> It assigns to newMethod. I suspect it returns currentClass because a) the
> return type was always sqInt because Slang didn't support void functions, and
> b) currentClass is a value in hand so probably in a register and hence cheap
> to return.
Ok
I was looking for an example to show a real lookup for the students that are
implementing ObjVlisp
Now I will see if I show them this method.
>> - what is the invariant?
>> that currentclass always point to the currently looked up class and
>> newMethod is the found method?
>
>
> The input arguments are messageSelector, argumentCount and its argument,
> class. The VM suffers somewhat from being cluttered with global variables,
> which is I think a legacy of the blue-book specification (the Smalltalk code
> that was used to implement Interpreter in VMMaker) being derived from the
> Alto and Dorado implementations in microcode. It would be nicer if there
> were fewer variables, but e.g. supplying argumentCount as a parameter
> throughout all the message handling routines can be difficult, especially
> when things like perform: and MNU change the argumentCount during message
> send.
I clearly see what you mean.
>
>> - why lookupMethodFor: selector InDictionary: dictionary is defined in
>> StackInterpreter but never used
>> only in CoInterpreter?
>
>
> Well, it belongs in StackInterpreter and could be used in the other lookup
> methods. I was probably considering rewriting the other lookup routines to
> use lookupMethodFor: InDictionary: but didn't get round to it.
ok I see.
While reading directly the see code I was wondering why you generate the ifdef
for different bytecode set?
Is it that you would have to call another object and that it would not have the
same instance variables.
Because I was thinking that such variation points could be handled by the
different interpreter subclasses.
>>
>> Thanks
>>
>>
>> lookupMethodInClass: class
>> | currentClass dictionary found |
>> <inline: false>
>> self assert: class ~= objectMemory nilObject.
>> currentClass := class.
>> [currentClass ~= objectMemory nilObject]
>> whileTrue:
>> [dictionary := objectMemory fetchPointer: MethodDictionaryIndex
>> ofObject: currentClass.
>>
>> *** trick with the cannotInterpret ***
>> dictionary = objectMemory nilObject ifTrue:
>> ["MethodDict pointer is nil (hopefully due a swapped
>> out stub)
>> -- raise exception #cannotInterpret:."
>> self createActualMessageTo: class.
>> messageSelector := objectMemory splObj:
>> SelectorCannotInterpret.
>> self sendBreak: messageSelector + BaseHeaderSize
>> point: (objectMemory lengthOf: messageSelector)
>> receiver: nil.
>> ^self lookupMethodInClass: (self superclassOf:
>> currentClass)].
>> *** trick with the cannotInterpret end ***
>>
>> found := self lookupMethodInDictionary: dictionary.
>> found ifTrue: [^currentClass].
>> ^^^^^^^^^^^^^^^^^^^^^^^^^
>>
>> currentClass := self superclassOf: currentClass].
>>
>> "Could not find #doesNotUnderstand: -- unrecoverable error."
>> messageSelector = (objectMemory splObj: SelectorDoesNotUnderstand)
>> ifTrue:
>> [self error: 'Recursive not understood error encountered'].
>>
>> "Cound not find a normal message -- raise exception #doesNotUnderstand:"
>> self createActualMessageTo: class.
>> messageSelector := objectMemory splObj: SelectorDoesNotUnderstand.
>> self sendBreak: messageSelector + BaseHeaderSize
>> point: (objectMemory lengthOf: messageSelector)
>> receiver: nil.
>> ^self lookupMethodInClass: class
>>
>>
>> if (found) {
>> return currentClass;
>> }
>>
>>
>> static sqInt
>> lookupMethodInClass(sqInt class)
>> {
>> // StackInterpreter>>#lookupMethodInClass: DECL_MAYBE_SQ_GLOBAL_STRUCT
>> sqInt currentClass;
>> sqInt dictionary;
>> sqInt found;
>> sqInt header;
>> sqInt index;
>> sqInt length;
>> sqInt mask;
>> sqInt methodArray;
>> sqInt nextSelector;
>> sqInt sz;
>> sqInt wrapAround;
>>
>> assert(class != (nilObject()));
>> currentClass = class;
>> while (currentClass != GIV(nilObj)) {
>> dictionary = longAt((currentClass + BaseHeaderSize) + (MethodDictionaryIndex
>> << ShiftForWord));
>> if (dictionary == GIV(nilObj)) {
>>
>> /* ifTrue: */
>>
>> createActualMessageTo(class);
>> GIV(messageSelector) = longAt((GIV(specialObjectsOop) +
>> BaseHeaderSize) + (SelectorCannotInterpret << ShiftForWord));
>> sendBreakpointreceiver(GIV(messageSelector) +
>> BaseHeaderSize, lengthOf(GIV(messageSelector)), null);
>> return lookupMethodInClass(longAt((currentClass +
>> BaseHeaderSize) + (SuperclassIndex << ShiftForWord)));
>> }
>> /* begin lookupMethodInDictionary: */
>> /* begin fetchWordLengthOf: */
>> /* begin sizeBitsOf: */
>> header = longAt(dictionary);
>> sz = ((header & TypeMask) == HeaderTypeSizeAndClass
>> ? (longAt(dictionary - (BytesPerWord * 2))) &
>> LongSizeMask
>> : header & SizeMask);
>> length = ((usqInt) (sz - BaseHeaderSize)) >> ShiftForWord;
>> mask = (length - SelectorStart) - 1;
>>
>> /* messageSelector */
>>
>> index = SelectorStart + (mask & (((GIV(messageSelector) & 1)
>> ? (GIV(messageSelector) >> 1)
>> : (((usqInt) (longAt(GIV(messageSelector)))) >> HashBitsOffset) &
>> HashMaskUnshifted)));
>> wrapAround = 0;
>> while (1) {
>> nextSelector = longAt((dictionary + BaseHeaderSize) + (index <<
>> ShiftForWord));
>> if (nextSelector == GIV(nilObj)) {
>> found = 0;
>> goto l1;
>> }
>> if (nextSelector == GIV(messageSelector)) {
>> methodArray = longAt((dictionary + BaseHeaderSize) + (MethodArrayIndex <<
>> ShiftForWord));
>> GIV(newMethod) = longAt((methodArray +
>> BaseHeaderSize) + ((index - SelectorStart) << ShiftForWord));
>> found = 1;
>> goto l1;
>> }
>> index += 1;
>> if (index == length) {
>> if (wrapAround) {
>> found = 0;
>> goto l1;
>> }
>> wrapAround = 1;
>> index = SelectorStart;
>> }
>> }
>> found = 0;
>> l1: /* end lookupMethodInDictionary: */;
>> if (found) {
>> return currentClass;
>> }
>> currentClass = longAt((currentClass + BaseHeaderSize) +
>> (SuperclassIndex << ShiftForWord));
>> }
>> if (GIV(messageSelector) == (longAt((GIV(specialObjectsOop) +
>> BaseHeaderSize) + (SelectorDoesNotUnderstand << ShiftForWord)))) {
>> error("Recursive not understood error encountered");
>> }
>> createActualMessageTo(class);
>> GIV(messageSelector) = longAt((GIV(specialObjectsOop) + BaseHeaderSize)
>> + (SelectorDoesNotUnderstand << ShiftForWord));
>> sendBreakpointreceiver(GIV(messageSelector) + BaseHeaderSize,
>> lengthOf(GIV(messageSelector)), null);
>> return lookupMethodInClass(class);
>> }
>>
>>
>>
>>
>
>
>
>
> --
> best,
> Eliot
