Please confirm/deny that MethodContext sender is nilled by the Interpreter.

I while ago, while studying Eliot's factorial copy example I made the mistake of assuming that since the sender of the MethodContext was the UndefinedObject (which is the Nil object) that that was why the sender was nil.

Eliot corrected me, writing:



and ends up at <primitive:188> in Object >>withArgs: argArray executeMethod: compiledMethod

{A whole bunch of stuff happens in System Space that I am do not know how to trace yet--but eventually, the return must happen....so..}


In the BlueBook on page 608, There is a section on Return Bytecodes where bytecode 123 does set the sender nil.

returnBytecode
   currentBytecode = 120
      ifTrue: [tself returnValue: receiver
                     to: self sender].
   currentBytecode = 121
      ifTrue: [tself returnValue: TruePointer
                     to: self sender].
   currentBytecode = 122
      ifTrue: [tself returnVatue: FalsePointer
                     to: self sender].
  currentBytecode = 123
      ifTrue: [tself returnValue: NilPointer
                     to: self sender].

Which exists on Squeak's Interpreter and is mapped to instance method

Interpreter >> returnNil.



and finally, Interpreter >> commonReturn


that seems the most possible path to me.

Conversely, any possibility of the sender being nilled in User Space would have to call
ContextPart>>privSender: aContext


Browsing the senders of that method paired with no apparent semaphores in the Compiler method, leads me to conclude it happens in system space.

Does that sound like its in the ballpark? Details are not neccessary as my goal was to just account for every variable we see in a Context.

thx

tty

Yep:

thisCntx := activeContext.

[thisCntx = localCntx]

whileFalse:

["climb up stack to localCntx"

contextOfCaller := objectMemory fetchPointer: SenderIndex ofObject: thisCntx.

"zap exited contexts so any future attempted use will be caught"

objectMemory storePointerUnchecked: SenderIndex ofObject: thisCntx withValue: nilOop.

objectMemory storePointerUnchecked: InstructionPointerIndex ofObject: thisCntx withValue: nilOop.

reclaimableContextCount > 0 ifTrue:

["try to recycle this context"

reclaimableContextCount := reclaimableContextCount - 1.

objectMemory recycleContextIfPossible: thisCntx].

thisCntx := contextOfCaller].

- Bert -