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COW cleanup patch (1583966):

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1. perform deep comparison for the classes for which it makes sense in the
   ports where this wasn't done yet
2. remove (shallow) comparison operators for the classes for which it does
   not make sense (such as wxBitmap)
3. makes wxBitmap use COW on all ports
4. adds wxObject::IsRefTo()
5. centralizes and improves COW docs


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42752 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
This commit is contained in:
Vadim Zeitlin
2006-10-30 19:26:48 +00:00
parent 8d1517cef2
commit 55ccdb93e4
102 changed files with 310 additions and 639 deletions
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36
docs/latex/wx/trefcount.tex
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@@ -1,6 +1,6 @@
\section{Reference counting}\label{trefcount}
\subsection{Reference counting and why you shouldn't care about it}\label{refcount}
\subsection{Why you shouldn't care about it}\label{refcount}
Many wxWidgets objects use a technique known as \it{reference counting}, also known
as {\it copy on write} (COW).
@@ -19,22 +19,54 @@ is not seen from the outside of the class - in any case, the result of any
operation on it is the same.
\subsection{List of reference-counted wxWidgets classes}\label{refcountlist}
\subsection{Object comparison}\label{refcountequality}
The $==$ and $!=$ operators of \helpref{wxWidgets COW objects}{refcountlist}
always do a {\tt deep} comparison.
This means that the equality operator will return \true if two objects are
identic and not only if they share the same data.
Note that wxWidgets follows the {\it STL philosophy}: when a comparison operator cannot
be implemented efficiently (like for e.g. wxImage's $==$ operator which would need to
compare pixel-by-pixel the entire image's data), it's not implemented at all.
That's why not all reference-counted wxWidgets classes provide comparison operators.
Also note that if you only need to do a {\tt shallow} comparison between two
\helpref{wxObject}{wxobject}-derived classes, you should not use the $==$ and $!=$ operators
but rather the \helpref{wxObject::IsRefTo}{wxobjectisrefto} function.
\subsection{Object destruction}\label{refcountdestruct}
When a COW object destructor is called, it may not delete the data: if it's shared,
the destructor will just decrement the shared data's reference count without destroying it.
Only when the destructor of the last object owning the data is called, the data is really
destroyed. As for all other COW-things, this happens transparently to the class users so
that you shouldn't care about it.
The following classes in wxWidgets have efficient (i.e. fast) assignment operators
and copy constructors since they are reference-counted:
\helpref{wxAcceleratorTable}{wxacceleratortable}\\
\helpref{wxAnimation}{wxanimation}\\
\helpref{wxBitmap}{wxbitmap}\\
\helpref{wxBrush}{wxbrush}\\
\helpref{wxCursor}{wxcursor}\\
\helpref{wxFont}{wxfont}\\
\helpref{wxIcon}{wxicon}\\
\helpref{wxImage}{wximage}\\
\helpref{wxMetafile}{wxmetafile}\\
\helpref{wxPalette}{wxpalette}\\
\helpref{wxPen}{wxpen}\\
\helpref{wxRegion}{wxregion}\\
\helpref{wxRegionIterator}{wxregioniterator}\\
\helpref{wxString}{wxstring}
Note that the list above reports the objects which are reference-counted in all ports of
wxWidgets; some ports may use this tecnique also for other classes.
\subsection{Make your own reference-counted class}\label{wxobjectoverview}
Reference counting can be implemented easily using \helpref{wxObject}{wxobject}