On 2021-12-30T20:08:48+01:00, christoph.thiede at student.hpi.uni-potsdam.de wrote:

> Hi all,
> 
> the docs on suspendedContext in the Process class comment say:
> 
>     if nil, then I am either the active process or I have been terminated.  If not nil it is the Context at the hot end of my stack
> 
> To me, this would indicate the following invariant:
> 
>     self assert: Processor activeProcess suspendedContext isNil.
> 
> However, this invariant is violated if you simulate this expression rather executing it:
> 
>     (Process
>         forBlock: [self assert: Processor activeProcess suspendedContext isNil]
>         runUntil: [:ctx | ctx isDead or: [ctx selector = #defaultAction]])
>             resume.
> 
> Do you think this is a bug and should be fixed? We could do this by patching all assignors to suspendedContext in the 'changing suspended state' protocol on Process, maybe even as a small pattern like this:
> 
>     step
> 
>         ^ self doStep: [:ctx | ctx step]
> 
>     stepToCallee
>         "Step until top context changes"
> 
>         ^ self doStep: [:ctx | | ctxt |
>             ctxt := ctx.
>             [ctxt == ctx] whileTrue: [ctxt := ctxt step].
>             ctxt]
> 
>     doStep: aBlock
>     
>         | ctxt |
>         ctxt := suspendedContext.
>         suspendedContext := nil.
>         ^ suspendedContext := Processor activeProcess
>             evaluate: [aBlock value: ctxt]
>             onBehalfOf: self
> 
> Where #doStep: would handle the effective process and read, set to nil, and set again the suspendedContext of the receiver. Disclaimer: The above is pseudocode only so far.
> 
> Or isn't this worth the overhead and the invariant above has only to be valid for processes that are executed by the VM? :-)
> 
> Best,
> Christoph
> 
> ---
> Sent from Squeak Inbox Talk
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Addendum: In some situations, the suspendedContext during simulation might even be out of date, for instance, inside a #stepToSendOrReturn.
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