On 01/08/2014 12:27 PM, Even Rouault wrote:
Le mercredi 08 janvier 2014 11:10:58, Tamas Szekeres a écrit :
Hi Devs,
Is that intentional that we don't call ReleaseResultset within the
destructor of the OGR Layer object?
The OGR Layer object has generally no pointer to the datasource from which it
originates (well, at the swig level we could probably attach one), so you
cannot call ReleaseResultSet
In the Perl bindings a link between OGR datasource and layer objects is
maintained and there is an explicit destructor for layer objects, which
may implicitly destruct a datasource object if one is left dangling.
Implicit because it is left for Perl to decide.
It's a good point that the ReleaseResultSet should be made a no-op and
hide it into the layer destructor. I'll look into implementing it in the
Perl bindings.
I assume it would be a good thing to implement this kind of machinery in
the Swig bindings but it may be a complex task.
Ari
Actually the destructor is not even
generated (at least for the C# API)
That must be the case of all bindings, because the OGR Layer object has no
destructor in its API. OGR C++ Layers obtained by OGRDataSource::GetLayer()
are owned by the C++ OGRDataSource and destroyed by it.
which seems to be an improper solution
and leads to memory leaks, definitely. However ReleaseResultset is exposed
in the API, but it's fairly dangerous to let the user decide whether to
call this method or not.
Yes, that's not very popular in garbage collected languages to let the user
deal with memory management...
In my understanding the destructor of the Layer object should look
something like the destructor of the DataSource (but calling
ReleaseResultset instead of ReleaseDatasource).
Actually you should distinguish how the Layer object has been created : if it
comes from GetLayer() or ExecuteSQL()
However modifying the code
this way, may lead to a crash for the existing code which call
ReleaseResultset directly.
Yes, that would cause breakage in all existing code. The alternative would be
that the public SWIG ReleaseResultSet() becomes a no-op and the destructor of
SWIG Layer object call OGR_DS_ReleaseResultSet() when appropriate.
Any opinion?
Best regards,
Tamas
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