Hi Max,

On Tue, Sep 16, 2014 at 11:05 AM, Max Leske <maxleske@gmail.com> wrote:

Hi

As always when I want to check if a process has died I get very confused by #isTerminated and I��m wondering if I just don��t get how it��s supposed to work or if there are others that share my confusion.

Old implementation:

isTerminated

�� self isActiveProcess ifTrue: [^ false].
�� ^suspendedContext isNil
�� or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess.
�� If so, and the pc is greater than the startpc, the bock has alrteady sent and returned
�� from value and there is nothing more to do."
�� suspendedContext isBottomContext
�� and: [ suspendedContext pc > suspendedContext startpc ] ]

Pharo 4 implementation:

isTerminated
�� self isActiveProcess ifTrue: [^ false].
�� ^suspendedContext isNil
�� or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess.
�� If so, and the pc is greater than the startpc, the bock has alrteady sent and returned
�� from value and there is nothing more to do.��
�� suspendedContext isBottomContext
�� and: [ suspendedContext isDead not ��<�� new"
�� and: [ suspendedContext pc > suspendedContext startpc ] ] ]

The old implementation would break if the suspended context was dead (i.e. the pc was nil) because the send of #> would produce an MNU.
The new implementation doesn��t fix that, even though it looks like it at first glance: if the pc is nil, the #> send will still happen -> MNU.

Off the top of my head it would seem that it should be isDead or: [] not isDead not and:

isTerminated
�� self isActiveProcess ifTrue: [^ false].
�� ^suspendedContext isNil
�� or: ["If the suspendedContext is the bottomContext it is the block in Process>>newProcess.
�� If so, and the pc is greater than the startpc, the bock has alrteady sent and returned
�� from value and there is nothing more to do.��
�� suspendedContext isBottomContext
�� and: [ suspendedContext isDead

�� or: [ suspendedContext pc > suspendedContext startpc ] ] ]��

isDead
�� ^ pc isNil

and maybe (suspendedContext pc ifNil: [true] ifNotNil: [:pc| pc��> suspendedContext startpc]) is more obvious.

Anyway, neither implementation will reliably tell me if the process has been terminated:
- an inactive process will be suspended when #terminate is sent and report that it has not been terminated (#isSuspended -> true, #isTerminated -> false)

except that it *hasn't* been terminated, it is merely in the process of termination. ��It isn't terminated until all unwind blocks have run, right?

��

- a properly terminated process will raise an MNU (although apparently not always��?)

but that's a bug the change I suggested will fix.

��

- all the states in between: no clue

I would like to know two things:
1. how can I check if a process has already *received* a #terminate? (I would then assume that the process will die eventually)

I don't think you can without putting a critical section around terminate and adding some process-specific variable that is set when you send terminate. ��termination is not instantaneous (unwind blocks have to be run), so it is potentially interruptible.

��

2. how can I check if a process is *actually* dead? (in case a ��half dead�� process will still unwind or whatever)

see above.

��

What would be necessary to make those tests (or better ones) possible (rewrite the whole process implementation?)?

Cheers,
Max

--
best,

Eliot