[Vm-dev] [VM-dev] Terminated process with zero pc

[Denis Kudriashov]

вт, 5 мая 2020 г. в 20:52, Eliot Miranda <eliot.miranda at gmail.com>:

>
> Hi Denis,
>
> On May 5, 2020, at 12:39 PM, Denis Kudriashov <dionisiydk at gmail.com>
> wrote:
>
> 
> Hi.
>
> I encounter interesting behavior of process termination. I can't reproduce
> it locally but I have constantly failing test on Pharo CI (as part of full
> test suite) due to following conditions:
>
> ended := false.
> process := [ Processor activeProcess suspend. ended := true]
>                        forkAt: Processor activePriority + 1.
> self assert: process isSuspended description: 'should be suspended'.
>
> process resume.
>
> self assert: ended description: 'last statement is done'.
> self assert: process suspendedContext pc equals: 0
>
> When I try to run it locally the pc is always greater than #startpc.
> On CI the test very rarely behaves same way. The process is always
> finished (#ended is true) but in most of runs the pc of #terminate context
> is somehow reset to zero (probably related to the order of overall test
> suite). .
>
> In Pharo succeed process ends here:
>
> terminate
>             ...........
>
>  self isActiveProcess ifTrue: [
>
> thisContext terminateTo: nil.
>
> self suspend ]
>
>
> It seems that Context>>#terminateTo: can reset the pc to zero under some
> condition (jitter related?).
>
>
> The JIT maps machine code PCs to bytecode PCs whenever the pc is accessed
> of a context which is running JITted code.  If the mapping fails then 0 may
> be returned.  But this is evidence of a bug in the mapping computation.
>

And in that case Process>>terminate would be a jitted method context. In
Pharo it is quite monstrous:

https://github.com/pharo-project/pharo/blob/7fc0df20a60bfbdf06e7fa6f21cfdc9bba81c3cc/src/Kernel/Process.class.st#L679
I will try to rerun my test with smaller refactored version.
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