Qt

As you know QMap/QHash are little bit faster than std::map and std::unordered_map … but why? I have no ideas about this before I have used them in high-load muti-thread application. I send data in QHash via queued signal/slot between threads. Anything looks fine, but 1-2 times per day application gets segfault. It was very strange because it crashed after different count iterations but it was millions iterations. GDB shows something like this: #0 0x00007f8421029107 in __GI_raise (sig=sig@entry=6) at ../nptl/sysdeps/unix/sysv/linux/raise.c:56 #1 0x00007f842102a4e8 in __GI_abort () at abort.c:89 #2 0x00007f8421067044 in __libc_message (do_abort=do_abort@entry=1, fmt=fmt@entry=0x7f8421159c40 "*** Error in `%s': %s: 0x%s ***\n") at ../sysdeps/posix/libc_fatal.c:175 #3 0x00007f842106c81e in malloc_printerr (action=1, str=0x7f8421159d90 "double free or corruption (out)", ptr=<optimized out>) at malloc.c:4996 #4 0x00007f842106d526 in _int_free (av=<optimized out>, p=<optimized out>, have_lock=0) at malloc.c:3840 #5 0x00007f8421ede054 in QHashData::free_helper (this=0x7f8418003a80, node_delete=0x40b324 <QHash<unsigned long, logdata>::deleteNode2(QHashData::Node*)>) at tools/qhash.cpp:496 #6 0x000000000040b364 in QHash<unsigned long, logdata>::freeData (this=0x7f84180bb5e0, x=0x7f8418003a80) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qhash.h:600 #7 0x000000000040f208 in QHash<unsigned long, logdata>::~QHash (this=0x7f84180bb5e0, __in_chrg=<optimized out>) at /usr/include/x86_64-linux-gnu/qt5/QtCore/qhash.h:310 after some days of hard debug, Qt source code reading and liters of green tea i have found that different instances of QHash (and also QMap) may share some data structures.

To compile global menu plugin (as show in previous post) we need also one-line code modification due to using Qt 5.4 in QtCreator: --- appmenuplatformmenubar.cpp.orig 2014-12-12 14:02:46.059940656 +0100 +++ appmenuplatformmenubar.cpp 2014-12-12 14:02:55.943940215 +0100 @@ -301,7 +301,7 @@ KdeAppMenuPlatformTheme::KdeAppMenuPlatformTheme(const QString &kdeHome, int kdeVersion) - : QKdeTheme(kdeHome, kdeVersion) + : QKdeTheme(QStringList(kdeHome), kdeVersion) { }

What is is and why we need it? From the Qt documentation we know that “Qt’s meta-object system provides the signals and slots mechanism for inter-object communication, run-time type information, and the dynamic property system.” [1]. I hope everyone knows what is signal-slot in Qt and why you need Q_OBJECT macro at the beginning of each class declaration. Meta-object is also used for object casting using qobject_cast template function. It’s much more safe then build-in C++ cast functions and often is much faster.

I have just installed Qt 5.3.1 from qt-project.org and…. Qt Creator doesn’t supports global menu in Unity :-( Goggling doesn’t helps me at all. After a little bit tracing I see that it uses it’s own plugins directory and of course it have no libappmenu-qt5.so So we need just few commands to fix this: sudo apt−get install libgtk2.0−dev libdbusmenu−qt5−dev cd /tmp apt−get source appmenu−qt5 cd appmenu−qt5−0.3.0+14.04.20140415/src ~/Qt/5.3/gcc_64/bin/qmake src.pro make test