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58 lines
1.9 KiB
Text
58 lines
1.9 KiB
Text
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Preface:
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======
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You've probably noticed the epic struggle we've had with Amarok 2
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hanging on exit. After _months_ of tinkering I've now been able to
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identify and fix this issue. This document explains how to prevent
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such issues in the future.
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What is a static object?
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=================
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A static object is being initialized on program start, and will only
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become instantiated once. It's conveniently used with the singleton
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design pattern, e.g. in Amarok code.
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Example:
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static AmarokMenu s_menu;
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What is so dangerous about static objects?
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================================
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A static object's destructor is called _after_ the QApplication
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destructor has been executed. This is fine for plain old datatypes
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(POD) like int, float, and pointers, as they do not have a destructor.
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It's also fine for objects with a trivial destructor that does not
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interfere with the rest of the program.
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The danger lies in using static objects that call other parts of the
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application in their destructor. This is e.g. true for most QObjects,
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which rely on the QApplication being intact. If the QApplication is
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destroyed before the static QObject's destructor is run, _bad_ things
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can happen. To name a few: Crashing, hanging, eating live kitten, or
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forcing you to use XMMS.
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How can I prevent these problems?
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==========================
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Use K_GLOBAL_STATIC, and use qAddPostRoutine() to ensure that the
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static object's destructor is called when QCoreApplication destructs.
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Example:
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class AmarokMenu : public QMenu
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{
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AmarokMenu();
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};
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K_GLOBAL_STATIC( AmarokMenu, s_menu )
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AmarokMenu::AmarokMenu()
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{
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// K_GLOBAL_STATIC is cleaned up *after* Q(Core)Application is gone
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// but we have to cleanup before -> use qAddPostRoutine
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qAddPostRoutine( s_menu.destroy );
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}
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Further reading:
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===========
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http://api.kde.org/4.0-api/kdelibs-apidocs/kdecore/html/group__KDEMacros.html
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Thanks for reading, and happy hacking :)
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