[patch 0/6] Smart pointers for CPdf v2

[Michal H. <ms...@gm...>]

Hi.  

This the second attempt for patchset which adds support for smart 
pointers also for CPdf. It is based on smart_ptr & weak_ptr pattern 
(thanks Jozo for coming with idea and implementation howto).

CPdf unlike other cobject is not so simple to wrap by shared_ptr because of
cyclic references (CPdf initializes IProperty objects which in turn refers
back to the pdf).  However changing IProperty::pdf from CPdf* to the
weak_ptr<CPdf> does the trick.

This change is rather intrusive to the rest of code, because it has to update
all usage of CPdf usage as well as update low-level objects.

Attached patches transform CPdf* to
	- weak_ptr<CPdf> for low-level
	- smart_ptr<CPdf> for high-level 

Patches coming in this patch-set are split to add features incrementally (see
separate emails for detailed description and patch). All of them are
compilable and higher one depends on the lower.

I have tested it on couple of documents (including PDF specification) and no
single problem occurred. I think that risk for future problems is only that 
we can force some nasty hidden bugs to be visible. I think it is better to 
have them visible even if it would mean that we will have kind of less
stable next release.

@Jozo could you comment changes, you would like to change (code style etc.).
@Martin could you check whether this is mergeable with your current QT4
branch or it simple produce too many conflicts that it should wait for 
later inclusion. 
If it is OK with you (give me ACK), I would suggest to include ASAP.

I don't want to create separate branch for this changes because I don't see
any potential for future changes here (besides sync with current CVS). Let
me know if I am missing something.

Changelog v1 -> v2
==================
Mainly sync with current CVS state and one additional patch (06) for
tests/bench code which has been added in the mean time.

* Patch 01
----------
Changes CPdf::getInstance from CPdf* to shared_ptr<CPdf> and updates all places
where the result is used.

* Patch 02
----------
Preparatory patch for observers. Rationale is that sometimes it is impossible
to unregister observers right in time and it is much easier to disable them
(IObserver::setActive(false)) which guarantees that they are not called and
noting bad can happen even if they are still registered.

As an example, consider CPdf transformed to shared_ptr which is deallocated in
the moment when the last reference is droped and shared_ptr itself is expired.
This means that also all weak_ptr to this shared_ptr are not valid. As a
result, ~CPdf is not allowed to dereference any objects or do anything where
_this field (see Patch 03) is needed. 

Unfortunately this is the problem for page tree observers which can't be
cleaned up sooner then in ~CPdf. Effectively, it is much simpler to deactivate
them rather then store them in a complicated way and add more overhead for
synchronization with changes in the page tree. 

Leaving observer registered and not active, of course, adds some memory
overhead, but all properties are discarded in ~CPdf anyway.  However, if there
are some pending references to them (due to scripting e.g.) they could trigger
observer with invalid data.  IObserver::isActive is checked before this can
actually happen.  On the other hand, setActive can be particularly useful for
situations where we would need temporarily disable notification.  This patch
can be added also separately without the rest.

* Patch 03
---------- 
Changes IProperty::pdf from CPdf* to weak_ptr<CPdf> and CPdf::_this field was
added. The first one is used to reffer to the pdf and the second one is used to
initialize all its properties.  Both of them are initialized from shared_ptr
returned by getInstance factory method and they are valid until shared_ptr
is alive.

* Patch 04
----------
Updates pdf deleter to also close file handle so that it can be removed from
CPdf. This is cleanup patch.

* Patch 05
----------
Updates design documentation for CPdf. I haven't found any mention about CPdf 
usage in cobjects.xml so I haven't updated that part (the one in cpdf.html 
should be enough anyway).

* Patch 06
----------
Simple update of tests/bench code to follow changes in CPdf::getInstance 
signature.

-- 
Michal Hocko