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

Denis Kudriashov dionisiydk at gmail.com
Mon May 11 21:34:33 UTC 2020


Hi Eliot.

I hope you did not spend your time on it. But if you did sorry for that.
I found that my issue is related to the Pharo bootstrap process. On CI we
run some kernel tests on fresh bootstrapped image to validate its
correctness. The code for this image is loaded from prebuilt  binary files
(containing precompiled methods). Nothing is recompiled there. So any
changes to related part of system requires special update of those files.

I am not sure what exactly happens in this tiny image. But I am quite
confident that it is not a VM issue.

Anyway thanks for your help


вт, 5 мая 2020 г. в 21:12, Denis Kudriashov <dionisiydk at gmail.com>:

>
> 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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