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From Philippe Mouawad <philippe.moua...@gmail.com>
Subject Re: Why do Functions that only have values as instance variable synchronize execute ?
Date Thu, 16 Oct 2014 21:30:27 GMT
On Thursday, October 16, 2014, Vladimir Sitnikov <
sitnikov.vladimir@gmail.com> wrote:

> > know wether CompoundVariables
> >which are in AbstractFunction subclasses values

You didn't read correctly:)
I think the main issue in this topic is to know wether CompoundVariables
which are in AbstractFunction subclasses values are thread safe (to the
exception of the non thread safe functions).

I am saying values field is array of compoundvariables , values field is in
AbstractFunction subclasses.
Of course CompoundVariables do not extend AbstractFunction !




>
> I am looking at commit e9228ccf8cca9b130c8730771693cbda024f8bb0
> git-svn-id: https://svn.apache.org/repos/asf/jmeter/trunk@1632410 and
> it reads that CompoundVariable does not extend AbstractFunction.
>
> >Today with synchronized we ensure that:
> >- While execute is being called by one thread, setParameters and other
> >execute() (from other threads) are blocked.
>
> I hope we can forbid setParameters usage after JMeterThread start.
> I understand bad things can happen if setParameters and execute are
> performed concurrently.
> I have very little idea how JMeter works internally, however I hope it does
> not do such things.
>
> >And due to the fact that it seems we never enter this condition of
> >CompoundVariable#execute()  which alters an instance variable :
>
> 1) If the CV in question is dynamic (in terms of isDynamic==true after each
> execution), then execute is thread safe modulo thread safety of embedded
> functions/variables.
>
> 2) If the CV in question is not dynamic (e.g. it does not contain
> Functions/SimpleVariable), then CV is NOT thread-safe: isDynamic=false &
> permanentResults =... are not ordered, thus if multiple threads execute
> CV.execute concurrently, then a thread can observe isDynamic==false and
> stale value in permanentResults (== it would return wrong results)


This is what needs to be checked, but it requires reading jmeter code, I
can understand it can take time :)

>
> I see the following options to fix that (in order of my preference):
> 2.1) move "isDynamic" initialization to setParameters. It looks like it is
> just a instanceof check. If we can't calculate initial value in
> setParameters method (i.e. we must compute the value at the first execution
> of execute method), then initial value of permanentResults can be set to
> null and the check in execute() should read "if (isDynamic ||
> permanentResults==null)".
>
> 2.2) You can make isDynamic volatile and write code as
> "permanentResults=results.toString();
> isDynamic=false" (in this order!). This is a minimal change.
>
>
> PS. I would replace LinkedList compiledElements with ArrayList: it is
> faster, more memory efficient, etc and I would use indexed iteration in
> execute (to avoid creation of Iterator). It does not hurt readability in
> that particular method from my point of view.
>
>
> Vladimir
>


-- 
Cordialement.
Philippe Mouawad.

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