RE: [sv-ec] FW: [sv-bc] for sv-ec: Persistence of covergroup instances

From: Jonathan Bromley <jonathan.bromley_at_.....>
Date: Mon May 15 2006 - 10:07:04 PDT
Arturo,

[does a covergroup instance go on collecting data even after its
parent object has become unreachable?]

> The answer depends on how one triggers the data sampling. If 
> sampling is
> done by explicit calls to the sample method then data collection stops
> as soon as the object becomes unreachable (you can't call it's sample
> method anymore). If the covergroup defines a coverage event then
> coverage will stop at some unspecified time when the object is garbage
> collected. To avoid over-collecting data in such situations, it is a
> good practice to explicitly call the stop method just prior to setting
> the reference to null.

Thanks, that makes very good sense.  However, I find it faintly troubling.
Coverage is just one way in which an object can have side-effects even
when it's unreachable; I can think of a few others, and doubtless you
can think of many more.  I don't recall seeing any discussion of this
in the LRM, and it's potentially a serious "gotcha!".  (Usual caveat:
please forgive me if it's there and I simply haven't noticed it.)
And in the absence of any specific rules in the LRM, it *could* be
argued that an object that has side-effects (by reaching into other
parts of the simulation) should never be garbage collected, precisely
because of those side-effects.
-- 
Jonathan Bromley, Consultant

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Received on Mon May 15 10:06:59 2006

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