> On 05/16/11 20:33, Vlad Khorsun wrote:
>>> Could you explain, please, semantics of addRef/release on public
>>> provider interfaces?
>>>
>>> The issue was discussed on this list with two possibilities:
>>> - when refCount = 1, release does things like detach, rollback, free,
>>> etc. It's what was implemented so far.
>>> - sometime mentioned also that detach/rollback/etc would not release,
>>> and user would need to explicit call it.
>>>
>>> But now Vlad says we can't call release when refCount = 1, and it's just
>>> there to decrement addRefs.
>>>
>>> This broke code I wrote based on discussed ideas, and I don't feel it's
>>> correct.
>>>
>>> (Also note Alex code in jrd.cpp and is clear he wrote code not using
>>> this new assumption.)
>> I assume there must be a kind of symmetry : attach\detach,
>> startTx\commit,
>> startTx\rollback, allocateStmt\freeStmt, addRef\release. From semantic POV
>> attach\detach is like constructor\destructor pair while addRef\release
>> should be
>> used for additional references only (i.e. not instead of destructor).
>>
>> So, if code calls attach\release - this is bug, as for me, and i see no
>> reasons
>> to write code in this way intentionally. I consider at as very bad practice
>> as it
>> could lead to the inexpected side effects (such as implicit rollback).
>
> Unfortunately release() is also a kind of dtor, and we can't report
> about an error that happened inside release(). Therefore the question is
> - what to do if one called release() for an object with refCount == 1? I
> assume that for us this is a kind of broken network connection, i.e.
> attachment is closed, transactions rolled back, etc. Bad style - but we
> must do something here...
Sure, we must do something and current code seems more-or-less OK
in this regards.
> Certainly, nothing prevents us from adding error reporting to our
> release. Should we do it?
We can introduce some special mode to report such errors using exceptions,
or write message into log, or even provide callback for debugging purposes.
But Adriano's question was about *semantics*. So, do you agree with me that
explicit detach() must be called by good code and not just release() ? And that
call of release() when refCount == 1 is a bug in caller's code ?
Regards,
Vlad
------------------------------------------------------------------------------
Achieve unprecedented app performance and reliability
What every C/C++ and Fortran developer should know.
Learn how Intel has extended the reach of its next-generation tools
to help boost performance applications - inlcuding clusters.
http://p.sf.net/sfu/intel-dev2devmay
Firebird-Devel mailing list, web interface at
https://lists.sourceforge.net/lists/listinfo/firebird-devel
