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Diffstat (limited to 'doc/src/groups.qdoc')
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diff --git a/doc/src/groups.qdoc b/doc/src/groups.qdoc index 731ac58..f7296a3 100644 --- a/doc/src/groups.qdoc +++ b/doc/src/groups.qdoc @@ -202,20 +202,6 @@ */ /*! - \group explicitly-shared - \ingroup groups - - \title Explicitly Shared Classes - \brief Classes that use explicit sharing to manage internal data. - - \keyword explicit sharing - \keyword explicitly shared - - Unlike many of Qt's data types, which use \l{implicit sharing}, these - classes use explicit sharing to manage internal data. -*/ - -/*! \group geomanagement \title Layout Classes \ingroup groups @@ -377,103 +363,6 @@ */ /*! - \group shared - \title Implicitly Shared Classes - \ingroup architecture - \ingroup groups - - \brief Classes that use reference counting for fast copying. - - \keyword implicit data sharing - \keyword implicit sharing - \keyword implicitly shared - \keyword reference counting - \keyword shared implicitly - \keyword shared classes - - Many C++ classes in Qt use implicit data sharing to maximize - resource usage and minimize copying. Implicitly shared classes are - both safe and efficient when passed as arguments, because only a - pointer to the data is passed around, and the data is copied only - if and when a function writes to it, i.e., \e {copy-on-write}. - - \tableofcontents - - \section1 Overview - - A shared class consists of a pointer to a shared data block that - contains a reference count and the data. - - When a shared object is created, it sets the reference count to 1. The - reference count is incremented whenever a new object references the - shared data, and decremented when the object dereferences the shared - data. The shared data is deleted when the reference count becomes - zero. - - \keyword deep copy - \keyword shallow copy - - When dealing with shared objects, there are two ways of copying an - object. We usually speak about \e deep and \e shallow copies. A deep - copy implies duplicating an object. A shallow copy is a reference - copy, i.e. just a pointer to a shared data block. Making a deep copy - can be expensive in terms of memory and CPU. Making a shallow copy is - very fast, because it only involves setting a pointer and incrementing - the reference count. - - Object assignment (with operator=()) for implicitly shared objects is - implemented using shallow copies. - - The benefit of sharing is that a program does not need to duplicate - data unnecessarily, which results in lower memory use and less copying - of data. Objects can easily be assigned, sent as function arguments, - and returned from functions. - - Implicit sharing takes place behind the scenes; the programmer - does not need to worry about it. Even in multithreaded - applications, implicit sharing takes place, as explained in - \l{Threads and Implicit Sharing}. - - \section1 Implicit Sharing in Detail - - Implicit sharing automatically detaches the object from a shared - block if the object is about to change and the reference count is - greater than one. (This is often called \e {copy-on-write} or - \e {value semantics}.) - - An implicitly shared class has total control of its internal data. In - any member functions that modify its data, it automatically detaches - before modifying the data. - - The QPen class, which uses implicit sharing, detaches from the shared - data in all member functions that change the internal data. - - Code fragment: - \snippet doc/src/snippets/code/doc_src_groups.qdoc 0 - - \section1 List of Classes - - The classes listed below automatically detach from common data if - an object is about to be changed. The programmer will not even - notice that the objects are shared. Thus you should treat - separate instances of them as separate objects. They will always - behave as separate objects but with the added benefit of sharing - data whenever possible. For this reason, you can pass instances - of these classes as arguments to functions by value without - concern for the copying overhead. - - Example: - \snippet doc/src/snippets/code/doc_src_groups.qdoc 1 - - In this example, \c p1 and \c p2 share data until QPainter::begin() - is called for \c p2, because painting a pixmap will modify it. - - \warning Do not copy an implicitly shared container (QMap, - QVector, etc.) while you are iterating over it using an non-const - \l{STL-style iterator}. -*/ - -/*! \group ssl \title Secure Sockets Layer (SSL) Classes \ingroup groups |