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/*
timer.qdoc
This file is part of GammaRay, the Qt application inspection and manipulation tool.
SPDX-FileCopyrightText: 2017 Klarälvdalens Datakonsult AB, a KDAB Group company <info@kdab.com>
Author: Volker Krause <volker.krause@kdab.com>
SPDX-License-Identifier: GPL-2.0-or-later
Contact KDAB at <info@kdab.com> for commercial licensing options.
*/
/*!
\example timer
\title Timer
\brief Analyze out of control timers.
\ingroup examples-gammaray
This examples shows GammaRay's capabilities in analyzing timer activity.
\section1 Problem
The example application shows two buttons, clicking any one of them is supposed to trigger
a deferred repaint of the application using two variations of a single-shot timer. In both
cases we however observe 100% CPU load afterwards.
Analyzing the CPU load with a debugger or profiler points to frequently firing timers, but
doesn't support us in finding where that timer actually came from.
\section1 Investigation
While the target application is running, open the \l{Timers} view in GammaRay
to obtain a list of all active timers. Sorting by \uicontrol{Total Wakeups} or
\uicontrol{Wakeups/Sec} allows to quickly identify timers running amok, such as the
recurring 0-interval timers in our example.
When working with a debug build, the context menu on the \l{Timers} view allows you directly
to navigate to the source code of the created timer object, or timer event receiver.
\section2 QTimer and QML Timer
When using timer objects such as QTimer or a QML Timer, you can further inspect those by
switching to the \l{Object Browser} via the context menu in the \l{Timers} view. In the object
browser the following inspection views are particularly useful for timer objects:
\list
\li The \l{Connections} view allows you to inspect to which action the timeout() signal is connected
to, which can help to identify the timer if source navigation is not available.
\li The \l{Methods} view allows to manually stop timers, to verify a specific timer is the source
of a problem, or to observe if it gets erroneously restarted.
\endlist
In the above example, we notice that the QTimer::singleShot property was accidentally left on false,
causing the timer to fire constantly.
\snippet timer/timer.cpp Missing setSingleShot
The \l{Signal Plotter} view of GammaRay can provide additional help in finding too frequently triggering timer
object, by means of observing their timeout signals.
\section2 QTimerEvent
Raw timer events are less commonly used than timer object and provide fewer options for runtime
diagnostics unfortunately.
In our example the source of the problem is a missing QObject::killTimer call in the QTimerEvent handler.
\snippet timer/timer.cpp Missing killTimer
*/
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