Re: [Pharo-project] [squeak-dev] #ensure: issues
FWIW, this quote from the following discussion on Squeak-dev distills
what I was trying (but failing) to demonstrate:
"We shouldn't stop trying to support well-behaved ensure blocks properly.
Because if we don't then ensure
becomes entirely random. Or can anyone here explain why it would be
reasonable to expect that this version works:
p := [[Processor yield] ensure:[Transcript show: 'finished']] fork.
Processor yield.
p terminate.
but this one doesn't:
p := [[] ensure:[Processor yield. Transcript show: 'finished']] fork.
Processor yield.
p terminate.
(we're using yield here to denote any kind of process switch) If the
only thing that determines whether an ensure block is executed is a
process switch, then we basically have random, non-predictable unwind
handling. Which is a problem that is entirely unrelated to whether the
unwind block is itself well-behaved or not. "
In a book with chapters discussing topics such as ensure and processes,
(based on Pharo 1.0 which is unlikely to contain any fixes for such an
issue), it deserves at least a mention.
Cheers,
Henry
Den 03.03.2010 15:33, skrev Levente Uzonyi:
> 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.
>>> 100 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 100. 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*
*
>>>
>>
>>
>> ___
>> Pharo-project mailing list
>> Pharo-project@lists.gforge.inria.fr
>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>>
>
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Re: [Pharo-project] [squeak-dev] #ensure: issues
btw henrik
does VW have the same behavior?
Stef
On Mar 4, 2010, at 11:38 AM, Henrik Johansen wrote:
> FWIW, this quote from the following discussion on Squeak-dev distills what I
> was trying (but failing) to demonstrate:
> "We shouldn't stop trying to support well-behaved ensure blocks properly.
> Because if we don't then ensure
> becomes entirely random. Or can anyone here explain why it would be
> reasonable to expect that this version works:
>
> p := [[Processor yield] ensure:[Transcript show: 'finished']] fork.
> Processor yield.
> p terminate.
>
> but this one doesn't:
>
> p := [[] ensure:[Processor yield. Transcript show: 'finished']] fork.
> Processor yield.
> p terminate.
>
> (we're using yield here to denote any kind of process switch) If the
> only thing that determines whether an ensure block is executed is a
> process switch, then we basically have random, non-predictable unwind
> handling. Which is a problem that is entirely unrelated to whether the
> unwind block is itself well-behaved or not. "
>
> In a book with chapters discussing topics such as ensure and processes,
> (based on Pharo 1.0 which is unlikely to contain any fixes for such an
> issue), it deserves at least a mention.
>
> Cheers,
> Henry
>
> Den 03.03.2010 15:33, skrev Levente Uzonyi:
>> 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.
100 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 100. 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*
> *
>>>
>>>
>>> ___
>>> Pharo-project mailing list
>>> Pharo-project@lists.gforge.inria.fr
>>> http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
>>>
>>
>> ___
>> Pharo-project mailing list
>>
>> Pharo-project@lists.gforge.inria.fr
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Re: [Pharo-project] [squeak-dev] #ensure: issues
In case anybody is interested, I tried Henrik's example in VAST:
| 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!Finish!
--
Cheers,
Peter
On Thu, Mar 4, 2010 at 1:19 PM, Stéphane Ducasse
wrote:
> btw henrik
>
> does VW have the same behavior?
>
> Stef
>
> On Mar 4, 2010, at 11:38 AM, Henrik Johansen wrote:
>
> > FWIW, this quote from the following discussion on Squeak-dev distills
> what I was trying (but failing) to demonstrate:
> > "We shouldn't stop trying to support well-behaved ensure blocks properly.
> > Because if we don't then ensure
> > becomes entirely random. Or can anyone here explain why it would be
> > reasonable to expect that this version works:
> >
> > p := [[Processor yield] ensure:[Transcript show: 'finished']] fork.
> > Processor yield.
> > p terminate.
> >
> > but this one doesn't:
> >
> > p := [[] ensure:[Processor yield. Transcript show: 'finished']] fork.
> > Processor yield.
> > p terminate.
> >
> > (we're using yield here to denote any kind of process switch) If the
> > only thing that determines whether an ensure block is executed is a
> > process switch, then we basically have random, non-predictable unwind
> > handling. Which is a problem that is entirely unrelated to whether the
> > unwind block is itself well-behaved or not. "
> >
> > In a book with chapters discussing topics such as ensure and processes,
> (based on Pharo 1.0 which is unlikely to contain any fixes for such an
> issue), it deserves at least a mention.
> >
> > Cheers,
> > Henry
> >
> > Den 03.03.2010 15:33, skrev Levente Uzonyi:
> >> 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.
> 100 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 100. 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*
> > *
>
> >>>
> >>>
> >>> ___
> >>> Pharo-project mailing list
> >>> Pharo-project@lists.gforge.inria.fr
> >>> http://lists.gforge.inria.fr/cgi-bin/mailman/lis
Re: [Pharo-project] [squeak-dev] #ensure: issues
Den 04.03.2010 13:19, skrev Stéphane Ducasse:
> btw henrik
>
> does VW have the same behavior?
>
> Stef
>
Short answer is no, Eliot described the details:
http://n4.nabble.com/ensure-issues-was-Re-Pharo-project-Pharo-by-Example-vol-2-new-chapter-available-tp1575765p1577519.html
Cheers,
Henry
> On Mar 4, 2010, at 11:38 AM, Henrik Johansen wrote:
>
>
>> FWIW, this quote from the following discussion on Squeak-dev distills what I
>> was trying (but failing) to demonstrate:
>> "We shouldn't stop trying to support well-behaved ensure blocks properly.
>> Because if we don't then ensure
>> becomes entirely random. Or can anyone here explain why it would be
>> reasonable to expect that this version works:
>>
>> p := [[Processor yield] ensure:[Transcript show: 'finished']] fork.
>> Processor yield.
>> p terminate.
>>
>> but this one doesn't:
>>
>> p := [[] ensure:[Processor yield. Transcript show: 'finished']] fork.
>> Processor yield.
>> p terminate.
>>
>> (we're using yield here to denote any kind of process switch) If the
>> only thing that determines whether an ensure block is executed is a
>> process switch, then we basically have random, non-predictable unwind
>> handling. Which is a problem that is entirely unrelated to whether the
>> unwind block is itself well-behaved or not. "
>>
>> In a book with chapters discussing topics such as ensure and processes,
>> (based on Pharo 1.0 which is unlikely to contain any fixes for such an
>> issue), it deserves at least a mention.
>>
>> Cheers,
>> Henry
>>
>> Den 03.03.2010 15:33, skrev Levente Uzonyi:
>>
>>> 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.
> 100 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 100. 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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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
2010/3/2 Levente Uzonyi :
> 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.
>
> 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.
> 100 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 100. 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?
>
>
What you think is expected behavior here:
a) process termination should start (be triggered) only when process
is outside of any #ensure: closure?
b) #ensure: block should always run to the end, despite anything?
Since you can't predict, what code will run inside ensure block, the
only guarantee that you having is actually
that your process will always enters such blocks during the normal
flow, or exception handling. But there is no guarantees that it will
be able to run the code inside it, when you terminating it.
> Cheers,
> Balázs & Levente
>
>
>>
>> *yay
>> Henry*
>> *
>
>
>
>
--
Best regards,
Igor Stasenko AKA sig.
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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
There might be not guarantee that it *can* run the code (an exception might be
raised ending the block, it might find itself waiting on an unsignaled
semaphore, etc.), but it should be **guaranteed** an opportunity to begin.
IIRC, Dolphin provides special handling to temporarily restart processes in
order to get this right.
Bill
-Original Message-
From: pharo-project-boun...@lists.gforge.inria.fr
[mailto:pharo-project-boun...@lists.gforge.inria.fr] On Behalf Of Igor Stasenko
Sent: Tuesday, March 02, 2010 4:57 PM
To: The general-purpose Squeak developers list
Cc: Pharo-project@lists.gforge.inria.fr
Subject: Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by
Example vol 2: new chapter available)
2010/3/2 Levente Uzonyi :
> 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.
>
> 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.
> 100 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 100. 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?
>
>
What you think is expected behavior here:
a) process termination should start (be triggered) only when process is outside
of any #ensure: closure?
b) #ensure: block should always run to the end, despite anything?
Since you can't predict, what code will run inside ensure block, the only
guarantee that you having is actually that your process will always enters such
blocks during the normal flow, or exception handling. But there is no
guarantees that it will be able to run the code inside it, when you terminating
it.
> Cheers,
> Balázs & Levente
>
>
>>
>> *yay
>> Henry*
>> *
>
>
>
>
--
Best regards,
Igor Stasenko AKA sig.
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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
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' ?
>
> 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.
> 100 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 100. 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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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
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.
100 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 100. 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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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
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.
>>> 100 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 100. 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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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
On Tue, 2 Mar 2010, Igor Stasenko wrote:
2010/3/2 Levente Uzonyi :
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.
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.
100 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 100. 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?
What you think is expected behavior here:
a) process termination should start (be triggered) only when process
is outside of any #ensure: closure?
b) #ensure: block should always run to the end, despite anything?
Since you can't predict, what code will run inside ensure block, the
only guarantee that you having is actually
that your process will always enters such blocks during the normal
flow, or exception handling. But there is no guarantees that it will
be able to run the code inside it, when you terminating it.
I'd expect it to be evaluated no matter what happens.
Levente
Cheers,
Balázs & Levente
*yay
Henry*
*
--
Best regards,
Igor Stasenko AKA sig.
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Re: [Pharo-project] [squeak-dev] #ensure: issues (was: Re: Pharo by Example vol 2: new chapter available)
> 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. I should have looked in the code. Now what is fun is that I did not not get at least an intuition. Anyway I learned something valuable. *Thanks* levente Now what is strange is that we always get this behavior because it relies on the fact that resetContents is not executed so if the process would be suspended a bit later it would be ok. Am'I correct? I will start to write a couple of chapter on concurrent programming because this is the best way to exorcize your doubts. I imagine that I will probably write for newbies and will need some concurrent minded people to catch up what I will write. Stef ___ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project
