Thanks Levente!
Cheers,
Alexandre
On 3 Mar 2010, at 11:33, Levente Uzonyi wrote:
> On Wed, 3 Mar 2010, Stéphane Ducasse wrote:
>
>>
>> On Mar 2, 2010, at 10:33 PM, Levente Uzonyi wrote:
>>
>>> On Tue, 2 Mar 2010, Henrik Sperre Johansen wrote:
>>>
>>>>
>>>>>> PS. For the not-so-faint-of-heart, open a Transcript and try
>>>>>> evaluating:
>>>>>> |proc|
>>>>>> proc := [[Transcript show: 'Start!'. ] ensure: [Transcript show:
>>>>>> 'Finish!' Processor yield.]] newProcess.
>>>>>> proc resume.
>>>>>> Processor yield.
>>>>>> proc suspend.
>>>>>> proc terminate.
>>>>> Why don't we get it printing?
>>>> Forgot a . there, supposed to be
>>>>
>>>> |proc|
>>>> proc := [[Transcript show: 'Start!'. ] ensure: [Transcript show:
>>>> 'Finish!'. Processor yield.]] newProcess.
>>>> proc resume.
>>>> Processor yield.
>>>> proc suspend.
>>>> proc terminate.
>>>>
>>>> on my machine it prints:
>>>> *Start!Start!Finish!
>>>
>>> The problem occurs because Transcript >> #endEntry (sent from
>>> #show:)
>>> takes a while to execute, so the process (proc) prints 'Start!', but
>>> it gets terminated before execution reaches #resetContents (#reset
>>> in
>>> Squeak). So 'Start!' is still in the stream. Then our process
>>> executes the
>>> #ensure: block and it prints 'Start!' and 'Finish!' too.
>>
>>
>> Thanks for the explanation levente!
>> But I'm still dizzy :) why Transcript show: 'Finish' would also
>> print 'start' ?
>
> Transcript is just a stream. #show: is just a combination of
> #nextPutAll: and #endEntry. #endEntry displays the contents of the
> stream and when that's done it removes everything from the stream
> with #resetContents. #resetContents is never executed, because the
> process is terminated before that. So the contents of the stream are
> kept and displayed again later.
>
>
> Levente
>
>>
>>>
>>> There's worse problem with #ensure: and #terminate is that, a
>>> process executing an #ensure: block can be terminated. If you
>>> evaluate this code:
>>>
>>> | process stage1 stage2 stage3 counter |
>>> stage1 := stage2 := stage3 := false.
>>> counter := 0.
>>> process := [
>>> [ stage1 := true ] ensure: [
>>> stage2 := true.
>>> 1000000 timesRepeat: [ counter := counter + 1 ].
>>> stage3 := true ] ] newProcess.
>>> process resume.
>>> Processor yield.
>>> process suspend.
>>> process terminate.
>>> 1000 milliSeconds asDelay wait.
>>> { stage1. stage2. stage3. counter } explore
>>>
>>> you will find that stage1 and stage2 is reached as expected, but
>>> stage3 is not and counter is less than 1000000. That's because the
>>> forked process started evaluating the #ensure: block, but it was
>>> terminated by our process.
>>>
>>> Is this the expected behavior when sending #terminate to a process
>>> which is evaluating an #ensure: block?
>>>
>>>
>>> Cheers,
>>> Balázs & Levente
>>>
>>>
>>>>
>>>> *yay
>>>> Henry*
>>>> *
>>>
>>
>>
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Alexandre Bergel http://www.bergel.eu
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