[concurrency-interest] JSR-133 Cookbook and exit monitor

√iktor Ҡlang viktor.klang at gmail.com
Wed Oct 8 09:05:03 EDT 2014


On Wed, Oct 8, 2014 at 2:36 PM, Remi Forax <forax at univ-mlv.fr> wrote:

>
> On 10/08/2014 02:30 PM, √iktor Ҡlang wrote:
>
>
>
> On Wed, Oct 8, 2014 at 2:09 PM, Remi Forax <forax at univ-mlv.fr> wrote:
>
>>
>> On 10/08/2014 12:51 PM, √iktor Ҡlang wrote:
>>
>> Sounds really bad if this is the case. I can totally understand eliding
>> locks that are re-taken in a nested fashion, but coarsening in terms of
>> coalescing neighboring acquisitions seems dubious.
>>
>>
>>  even in this case,
>> class Foo {
>>   public synchronized void setBar(Bar bar) { ... }
>>   public synchronized void setBaz(Baz baz) { ... }
>> }
>> ...
>>   Foo foo = ...
>>   foo.setBar(bar);
>>   foo.setBaz(baz);
>>
>> because sadly this code is very common :(
>>
>
>  Agreed. The case above is not really problematic since there are no
> invocations/reads/writes in between.
>
>
> sorry my code was not clear, I should have written:
>   Foo foo = ...
>   foo.setBar(this.bar);
>   foo.setBaz(this.baz);
>
> there is a load of the field baz in between the call to setBar and the
> call to setBaz.
>

It sounds like an (unhealthy?) possible interaction between roach motel
rule and lock coarsening?


>
> Rémi
>
>
>
>
>>
>> Rémi
>>
>>
>>
>> On Wed, Oct 8, 2014 at 12:19 PM, thurstonn <thurston at nomagicsoftware.com>
>> wrote:
>>
>>> Hello,
>>>
>>> If I read the  jsr-133 cookbook
>>> <http://gee.cs.oswego.edu/dl/jmm/cookbook.html>   correctly, given the
>>> following:
>>>
>>>
>>> <code>
>>> //y is a global, non-volatile
>>> enter monitor x
>>> ...
>>> //do some work not involving y
>>> . . .
>>> exit monitor x
>>> y = 43
>>>
>>> </code>
>>>
>>> then at least according to the JMM, the following execution is possible:
>>> <code>
>>> //y is a global, non-volatile
>>> enter monitor x
>>> ...
>>> //do some work not involving y
>>> y = 43
>>> exit monitor x
>>> </code>
>>>
>>> as in the first table in the cookbook, *normal stores* are allowed to be
>>> re-ordered before a *monitor exit* (but not before a *monitor enter*).
>>>
>>> Although the issue isn't really one involving memory consistency, is that
>>> really allowed?  Because *increasing* the size of a critical section
>>> seems .
>>> . . I don't know . . . unhealthy.
>>> What if the program code computed the first 1000 prime numbers or
>>> something
>>> and wrote them to a global array (after the monitor exit)?
>>>
>>> I was always under the impression that only the operations specified
>>> within
>>> a critical section would actually be executed between the enter/exit
>>> monitor
>>> pair
>>>
>>> NB: Although, presumably the runtime/CPU would only do this if the
>>> critical
>>> section was leading to CPU stalls or the like and so in reality, not
>>> really
>>> producing a longer critical section execution time
>>>
>>>
>>>
>>>
>>> --
>>> View this message in context:
>>> http://jsr166-concurrency.10961.n7.nabble.com/JSR-133-Cookbook-and-exit-monitor-tp11323.html
>>> Sent from the JSR166 Concurrency mailing list archive at Nabble.com.
>>> _______________________________________________
>>> Concurrency-interest mailing list
>>> Concurrency-interest at cs.oswego.edu
>>> http://cs.oswego.edu/mailman/listinfo/concurrency-interest
>>>
>>
>>
>>
>> --
>>  Cheers,
>>>>
>>
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>>
>>
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>>
>
>
> --
>  Cheers,
>>
>
>


-- 
Cheers,
√
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