qt_eventdispatcher_libevent

libevent-based event dispatcher for Qt

Features

• very fast :-)
• compatibile with Qt 4 (Qt 4.2+) and Qt 5
• does not use any private Qt headers
• passes Qt 4 and Qt 5 event dispatcher, event loop, timer and socket notifier tests

Unsupported Features

• QSocketNotifier::Exception (libevent offers no support for this)
• Qt 5/Windows only: QWinEventNotifier is not supported (registerEventNotifier() and unregisterEventNotifier() functions are currently implemented as stubs; libevent does not natively support Windows events and addition of the support to the event dispatcher will mean a completely different event loop code for Windows).

Requirements

• libevent >= 2.0.0 (the code seems to work with libevent 1.4.x but this has not been tested much — but the Qt tests are successfully passed though)
• Qt >= 4.2 (tests from tests-qt4 were run only on Qt 4.8.x, 4.5.4, 4.3.0, 4.2.1)

Build

cd src
qmake
make

Replace make with nmake if your are using Microsoft Visual C++.

The above commands will generate the static library and .prl file in ../lib directory.

Install

After completing Build step run

*NIX:

sudo make install

Windows:

nmake install

For Windows this will copy eventdispatcher_libevent.h and eventdispatcher_libevent_config.h to ../lib directory. For *NIX this will install eventdispatcher_libevent.h to /usr/include, libeventdispatcher_libevent.a and libeventdispatcher_libevent.prl to /usr/lib, eventdispatcher_libevent.pc to /usr/lib/pkgconfig.

Usage (Qt 4)

Simply include the header file and instantiate the dispatcher in main() before creating the Qt application object.

#include "eventdispatcher_libevent.h"
    
int main(int argc, char** argv)
{
    EventDispatcherLibEvent dispatcher;
    QCoreApplication app(argc, argv);

    // ...

    return app.exec();
}

And add these lines to the .pro file:

unix {
    CONFIG    += link_pkgconfig
    PKGCONFIG += eventdispatcher_libevent
}
else:win32 {
    include(/path/to/qt_eventdispatcher_libevent/lib/eventdispatcher_libevent.pri)
}

or

HEADERS += /path/to/eventdispatcher_libevent.h
LIBS    += -L/path/to/library -leventdispatcher_libevent

Usage (Qt 5)

Simply include the header file and instantiate the dispatcher in main() before creating the Qt application object.

#include "eventdispatcher_libevent.h"

int main(int argc, char** argv)
{
    QCoreApplication::setEventDispatcher(new EventDispatcherLibEvent);
    QCoreApplication app(argc, argv);

    // ...

    return app.exec();
}

And add these lines to the .pro file:

unix {
    CONFIG    += link_pkgconfig
    PKGCONFIG += eventdispatcher_libevent
}
else:win32 {
    include(/path/to/qt_eventdispatcher_libevent/lib/eventdispatcher_libevent.pri)
}

or

HEADERS += /path/to/eventdispatcher_libevent.h
LIBS    += -L/path/to/library -leventdispatcher_libevent

Qt 5 allows to specify a custom event dispatcher for the thread:

QThread* thr = new QThread;
thr->setEventDispatcher(new EventDispatcherLibEvent);

Interesting Facts

EventDispatcherLibEvent is more compatible with Qt 4.2.x and 4.3.x than the native UNIX event dispatcher from those Qt's.

For example, Qt 4.2.1 fails tst_QTimer::livelock(zero timer) and tst_QTimer::livelock(non-zero timer) tests ('tester.postEventAtRightTime' returned FALSE) and hangs in tst_QEventLoop::processEventsExcludeTimers test but EventDispatcherLibEvent passes them all!

It should, however, be noted that these tests were taken from Qt 4.8 :-)