[squeak-dev] Need help with identifying the problem

In VM w/o closures, i implemented a new primitive,
#primitiveInterrupt, which looks like following:

primitiveInterrupt
        "primitive"
        | context interruptProcess sched oldProc |
        self export: true.
        context := self stackTop.

        sched := self schedulerPointer.
        "check that we using a new scheduler , which having additional
instance variables:
         - interruptProcess
         - interruptedProcess"
        (self lastPointerOf: sched) >= (InterruptedProcessIndex *
BytesPerWord + BaseHeaderSize)
                ifFalse: [ ^ self primitiveFail ].

        oldProc := self fetchPointer: ActiveProcessIndex ofObject: sched.
        interruptProcess := self fetchPointer: InterruptProcessIndex ofObject: sched.
        oldProc == interruptProcess ifTrue: [
                "we are already in interrupt, proceed as with sending #value to block"
                ^ self primitiveValue
                ].
        self storePointer: InterruptedProcessIndex ofObject: sched withValue: oldProc.
        self storePointer: SuspendedContextIndex ofObject: interruptProcess
withValue: context.
        self putToSleep: oldProc.
        self transferTo: interruptProcess.

        self pop: 1 thenPush: self nilObject
       

A primitive is hooked in
BlockContext>>primInterrupt :

primInterrupt
        "Primitive. Evaluate the block in special interrupt process"
        <primitive: 'primitiveInterrupt' module: ''>
        self primitiveFail


And code, which is using it looks like following:

Processor>>interruptWith: aBlock
        "Interrupt the currently running process to evaluate given block
argument inside
        interrupt process"
        | result |
        [ result := aBlock value.  activeProcess suspend. ] asContext primInterrupt.
        ^ result
       
the VM crashing at attempt to return from aBlock value (it never gets
to the point for evaluating 'activeProcess suspend').

if i write code like following:

Processor>>interruptWith: aBlock
        "Interrupt the currently running process to evaluate given block
argument inside
        interrupt process"
        | result |
        [ [ result := aBlock value. ] value  activeProcess suspend. ]
asContext primInterrupt.
        ^ result

Then VM does not crashing, but silenty quits to OS.

The only way how i managed to make it work, is to do it as:

Processor>>interruptWith: aBlock
        "Interrupt the currently running process to evaluate given block
argument inside
        interrupt process"
        [ self runBlock: aBlock ] asContext primInterrupt.

and runBlock: aBlock is:

runBlock: aBlock
       
        aBlock value.
        activeProcess suspend.

it works fine, except that i unable to use the returned result. - i
could put it to instance variable.. but its a bit awkward :(

I suspect this somehow connected with the return to context who having
sender = nil. (a bottom context of process always having sender =
nil).
But i wonder, why my code not working, while code, which used for
#fork, it does? Any suggestions?

newProcess
        "Answer a Process running the code in the receiver. The process is not
        scheduled."

        <primitive: 19> "Simulation guard"
        ^ Process
                forContext:
                        [self value.
                        Processor terminateActive] asContext
                priority: Processor activePriority

here, the initial context of newly created process will point to:

[self value. Processor terminateActive]

and in my case, an initial context of interrupt process is set in
#primitiveInterrupt and points to:
[ result := aBlock value.  activeProcess suspend. ]

why i works for above case, but not for mine, no idea...

--
Best regards,
Igor Stasenko AKA sig.

On Wed, 29 Apr 2009 09:17:16 +0200, Igor Stasenko wrote:

Check(s) may lack this: any process can be in any state including the ones  
which you do not want and the ones which #transferTo: does not want.

(activeProcess suspend) you mean an instVar ??

Now with #activeProcess you are sending, versus the instVar above ??

> Then VM does not crashing, but silenty quits to OS.

Good luck :)

--
"If at first, the idea is not absurd, then there is no hope for it".  
Albert Einstein

2009/4/29 Klaus D. Witzel <[hidden email]>: at this stage i don't care.
Active process is healthy - because it runs.
An interrupt process is accessible only by scheduler, and scheduler
makes sure its in good shape. :)

yeah. why writing 'Processor activeProcess suspend', when self == Processor?
its just a typo. there is '.' missing.  I changed this code multiple
times trying multiple variants. And i can assure you that problem is
not because DNU :)
As i said, VM crashing/misbehaves after returning from send #value to
a block. So its really irrelevant what follows, i can write:

 [ result := aBlock value. ] value  foo bar zork.

and have the same result :)

>> Then VM does not crashing, but silenty quits to OS.
>
> Good luck :)
>

Actually, the problem is not relevant anymore because i changed a
strategy to simply have a primitive which does task switching.
Rest will be handled by scheduler process (including: scheduling
processes, signaling semaphores etc).

But still its would be good to know, what is wrong with it, to know
how to avoid it in future :)



--
Best regards,
Igor Stasenko AKA sig.