qt 6.5.1 original

examples/corelib/threads/CMakeLists.txt

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+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+qt_internal_add_example(semaphores)
+qt_internal_add_example(waitconditions)
+if(TARGET Qt6::Widgets)
+    qt_internal_add_example(mandelbrot)
+    qt_internal_add_example(queuedcustomtype)
+endif()

examples/corelib/threads/README

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+This folder contains examples for the use of the threading-related classes
+in Qt Core. For examples using the higher-level Qt Concurrent module,
+check out the "qtconcurrent" folder instead.
+
+Documentation for examples can be found via the Examples and Tutorials link
+in the main Qt documentation. The examples and their documentation can also
+be opened from the Examples tab of Qt Creator's Welcome mode.

examples/corelib/threads/doc/src/mandelbrot.qdoc

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+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example threads/mandelbrot
+    \title Mandelbrot Example
+    \ingroup qtconcurrent-mtexamples
+
+    \brief The Mandelbrot example demonstrates multi-thread programming
+    using Qt. It shows how to use a worker thread to
+    perform heavy computations without blocking the main thread's
+    event loop.
+
+    \image mandelbrot-example.png Screenshot of the Mandelbrot example
+
+    The heavy computation here is the Mandelbrot set, probably the world's most
+    famous fractal. These days, while sophisticated programs, such as
+    \l{https://xaos-project.github.io/}{XaoS}, provide real-time zooming in
+    the Mandelbrot set, the standard Mandelbrot algorithm is just slow enough
+    for our purposes.
+
+    In real life, the approach described here is applicable to a
+    large set of problems, including synchronous network I/O and
+    database access, where the user interface must remain responsive
+    while some heavy operation is taking place. The \l
+    {Blocking Fortune Client} example shows the same principle at
+    work in a TCP client.
+
+    The Mandelbrot application supports zooming and scrolling using
+    the mouse or the keyboard. To avoid freezing the main thread's
+    event loop (and, as a consequence, the application's user
+    interface), we put all the fractal computation in a separate
+    worker thread. The thread emits a signal when it is done
+    rendering the fractal.
+
+    During the time where the worker thread is recomputing the
+    fractal to reflect the new zoom factor position, the main thread
+    simply scales the previously rendered pixmap to provide immediate
+    feedback. The result doesn't look as good as what the worker
+    thread eventually ends up providing, but at least it makes the
+    application more responsive. The sequence of screenshots below
+    shows the original image, the scaled image, and the rerendered
+    image.
+
+    \table
+    \row
+    \li \inlineimage mandelbrot_zoom1.png
+    \li \inlineimage mandelbrot_zoom2.png
+    \li \inlineimage mandelbrot_zoom3.png
+    \endtable
+
+    Similarly, when the user scrolls, the previous pixmap is scrolled
+    immediately, revealing unpainted areas beyond the edge of the
+    pixmap, while the image is rendered by the worker thread.
+
+    \table
+    \row
+    \li \inlineimage mandelbrot_scroll1.png
+    \li \inlineimage mandelbrot_scroll2.png
+    \li \inlineimage mandelbrot_scroll3.png
+    \endtable
+
+    The application consists of two classes:
+
+    \list
+    \li \c RenderThread is a QThread subclass that renders
+       the Mandelbrot set.
+    \li \c MandelbrotWidget is a QWidget subclass that shows the
+       Mandelbrot set on screen and lets the user zoom and scroll.
+    \endlist
+
+    If you are not already familiar with Qt's thread support, we
+    recommend that you start by reading the \l{Thread Support in Qt}
+    overview.
+
+    \section1 RenderThread Class Definition
+
+    We'll start with the definition of the \c RenderThread class:
+
+    \snippet threads/mandelbrot/renderthread.h 0
+
+    The class inherits QThread so that it gains the ability to run in
+    a separate thread. Apart from the constructor and destructor, \c
+    render() is the only public function. Whenever the thread is done
+    rendering an image, it emits the \c renderedImage() signal.
+
+    The protected \c run() function is reimplemented from QThread. It
+    is automatically called when the thread is started.
+
+    In the \c private section, we have a QMutex, a QWaitCondition,
+    and a few other data members. The mutex protects the other data
+    member.
+
+    \section1 RenderThread Class Implementation
+
+    \snippet threads/mandelbrot/renderthread.cpp 0
+
+    In the constructor, we initialize the \c restart and \c abort
+    variables to \c false. These variables control the flow of the \c
+    run() function.
+
+    We also initialize the \c colormap array, which contains a series
+    of RGB colors.
+
+    \snippet threads/mandelbrot/renderthread.cpp 1
+
+    The destructor can be called at any point while the thread is
+    active. We set \c abort to \c true to tell \c run() to stop
+    running as soon as possible. We also call
+    QWaitCondition::wakeOne() to wake up the thread if it's sleeping.
+    (As we will see when we review \c run(), the thread is put to
+    sleep when it has nothing to do.)
+
+    The important thing to notice here is that \c run() is executed
+    in its own thread (the worker thread), whereas the \c
+    RenderThread constructor and destructor (as well as the \c
+    render() function) are called by the thread that created the
+    worker thread. Therefore, we need a mutex to protect accesses to
+    the \c abort and \c condition variables, which might be accessed
+    at any time by \c run().
+
+    At the end of the destructor, we call QThread::wait() to wait
+    until \c run() has exited before the base class destructor is
+    invoked.
+
+    \snippet threads/mandelbrot/renderthread.cpp 2
+
+    The \c render() function is called by the \c MandelbrotWidget
+    whenever it needs to generate a new image of the Mandelbrot set.
+    The \c centerX, \c centerY, and \c scaleFactor parameters specify
+    the portion of the fractal to render; \c resultSize specifies the
+    size of the resulting QImage.
+
+    The function stores the parameters in member variables. If the
+    thread isn't already running, it starts it; otherwise, it sets \c
+    restart to \c true (telling \c run() to stop any unfinished
+    computation and start again with the new parameters) and wakes up
+    the thread, which might be sleeping.
+
+    \snippet threads/mandelbrot/renderthread.cpp 3
+
+    \c run() is quite a big function, so we'll break it down into
+    parts.
+
+    The function body is an infinite loop which starts by storing the
+    rendering parameters in local variables. As usual, we protect
+    accesses to the member variables using the class's mutex. Storing
+    the member variables in local variables allows us to minimize the
+    amount of code that needs to be protected by a mutex. This ensures
+    that the main thread will never have to block for too long when
+    it needs to access \c{RenderThread}'s member variables (e.g., in
+    \c render()).
+
+    The \c forever keyword is, like \c foreach, a Qt pseudo-keyword.
+
+    \snippet threads/mandelbrot/renderthread.cpp 4
+    \snippet threads/mandelbrot/renderthread.cpp 5
+    \snippet threads/mandelbrot/renderthread.cpp 6
+    \snippet threads/mandelbrot/renderthread.cpp 7
+
+    Then comes the core of the algorithm. Instead of trying to create
+    a perfect Mandelbrot set image, we do multiple passes and
+    generate more and more precise (and computationally expensive)
+    approximations of the fractal.
+
+    We create a high resolution pixmap by applying the device
+    pixel ratio to the target size (see
+    \l{Drawing High Resolution Versions of Pixmaps and Images}).
+
+    If we discover inside the loop that \c restart has been set to \c
+    true (by \c render()), we break out of the loop immediately, so
+    that the control quickly returns to the very top of the outer
+    loop (the \c forever loop) and we fetch the new rendering
+    parameters. Similarly, if we discover that \c abort has been set
+    to \c true (by the \c RenderThread destructor), we return from
+    the function immediately, terminating the thread.
+
+    The core algorithm is beyond the scope of this tutorial.
+
+    \snippet threads/mandelbrot/renderthread.cpp 8
+    \snippet threads/mandelbrot/renderthread.cpp 9
+
+    Once we're done with all the iterations, we call
+    QWaitCondition::wait() to put the thread to sleep,
+    unless \c restart is \c true. There's no use in keeping a worker
+    thread looping indefinitely while there's nothing to do.
+
+    \snippet threads/mandelbrot/renderthread.cpp 10
+
+    The \c rgbFromWaveLength() function is a helper function that
+    converts a wave length to a RGB value compatible with 32-bit
+    \l{QImage}s. It is called from the constructor to initialize the
+    \c colormap array with pleasing colors.
+
+    \section1 MandelbrotWidget Class Definition
+
+    The \c MandelbrotWidget class uses \c RenderThread to draw the
+    Mandelbrot set on screen. Here's the class definition:
+
+    \snippet threads/mandelbrot/mandelbrotwidget.h 0
+
+    The widget reimplements many event handlers from QWidget. In
+    addition, it has an \c updatePixmap() slot that we'll connect to
+    the worker thread's \c renderedImage() signal to update the
+    display whenever we receive new data from the thread.
+
+    Among the private variables, we have \c thread of type \c
+    RenderThread and \c pixmap, which contains the last rendered
+    image.
+
+    \section1 MandelbrotWidget Class Implementation
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 0
+
+    The implementation starts with a few constants that we'll need
+    later on.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 1
+
+    The interesting part of the constructor is the
+    QObject::connect() call.
+
+    Although it looks like a standard signal-slot connection between
+    two \l{QObject}s, because the signal is emitted in a different
+    thread than the receiver lives in, the connection is effectively a
+    \l{Qt::QueuedConnection}{queued connection}. These connections are
+    asynchronous (i.e., non-blocking), meaning that the slot will be
+    called at some point after the \c emit statement. What's more, the
+    slot will be invoked in the thread in which the receiver lives.
+    Here, the signal is emitted in the worker thread, and the slot is
+    executed in the GUI thread when control returns to the event loop.
+
+    With queued connections, Qt must store a copy of the arguments
+    that were passed to the signal so that it can pass them to the
+    slot later on. Qt knows how to take of copy of many C++ and Qt
+    types, so, no further action is needed for QImage.
+    If a custom type was used, a call to the template function
+    qRegisterMetaType() would be required before the type
+    could be used as a parameter in queued connections.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 2
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 3
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 4
+
+    In \l{QWidget::paintEvent()}{paintEvent()}, we start by filling
+    the background with black. If we have nothing to paint yet (\c
+    pixmap is null), we display a message on the widget asking the user
+    to be patient and return from the function immediately.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 5
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 6
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 7
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 8
+
+    If the pixmap has the right scale factor, we draw the pixmap directly onto
+    the widget.
+
+    Otherwise, we create a preview pixmap to be shown until the calculation
+    finishes and translate the \l{Coordinate System}{coordinate system}
+    accordingly.
+
+    Since we are going to use transformations on the painter
+    and use an overload of QPainter::drawPixmap() that does not support
+    high resolution pixmaps in that case, we create a pixmap with device pixel
+    ratio 1.
+
+    By reverse mapping the widget's rectangle using the scaled painter matrix,
+    we also make sure that only the exposed areas of the pixmap are drawn.
+    The calls to QPainter::save() and QPainter::restore() make sure that any
+    painting performed afterwards uses the standard coordinate system.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 9
+
+    At the end of the paint event handler, we draw a text string and
+    a semi-transparent rectangle on top of the fractal.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 10
+
+    Whenever the user resizes the widget, we call \c render() to
+    start generating a new image, with the same \c centerX, \c
+    centerY, and \c curScale parameters but with the new widget size.
+
+    Notice that we rely on \c resizeEvent() being automatically
+    called by Qt when the widget is shown the first time to generate
+    the initial image.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 11
+
+    The key press event handler provides a few keyboard bindings for
+    the benefit of users who don't have a mouse. The \c zoom() and \c
+    scroll() functions will be covered later.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 12
+
+    The wheel event handler is reimplemented to make the mouse wheel
+    control the zoom level. QWheelEvent::angleDelta() returns the angle
+    of the wheel mouse movement, in eighths of a degree. For most mice,
+    one wheel step corresponds to 15 degrees. We find out how many
+    mouse steps we have and determine the resulting zoom factor.
+    For example, if we have two wheel steps in the positive direction
+    (i.e., +30 degrees), the zoom factor becomes \c ZoomInFactor
+    to the second power, i.e. 0.8 * 0.8 = 0.64.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 13
+
+    Pinch to zoom has been implemented with QGesture as outlined in
+    \l{Gestures in Widgets and Graphics View}.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp gesture1
+
+    When the user presses the left mouse button, we store the mouse
+    pointer position in \c lastDragPos.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 14
+
+    When the user moves the mouse pointer while the left mouse button
+    is pressed, we adjust \c pixmapOffset to paint the pixmap at a
+    shifted position and call QWidget::update() to force a repaint.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 15
+
+    When the left mouse button is released, we update \c pixmapOffset
+    just like we did on a mouse move and we reset \c lastDragPos to a
+    default value. Then, we call \c scroll() to render a new image
+    for the new position. (Adjusting \c pixmapOffset isn't sufficient
+    because areas revealed when dragging the pixmap are drawn in
+    black.)
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 16
+
+    The \c updatePixmap() slot is invoked when the worker thread has
+    finished rendering an image. We start by checking whether a drag
+    is in effect and do nothing in that case. In the normal case, we
+    store the image in \c pixmap and reinitialize some of the other
+    members. At the end, we call QWidget::update() to refresh the
+    display.
+
+    At this point, you might wonder why we use a QImage for the
+    parameter and a QPixmap for the data member. Why not stick to one
+    type? The reason is that QImage is the only class that supports
+    direct pixel manipulation, which we need in the worker thread. On
+    the other hand, before an image can be drawn on screen, it must
+    be converted into a pixmap. It's better to do the conversion once
+    and for all here, rather than in \c paintEvent().
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 17
+
+    In \c zoom(), we recompute \c curScale. Then we call
+    QWidget::update() to draw a scaled pixmap, and we ask the worker
+    thread to render a new image corresponding to the new \c curScale
+    value.
+
+    \snippet threads/mandelbrot/mandelbrotwidget.cpp 18
+
+    \c scroll() is similar to \c zoom(), except that the affected
+    parameters are \c centerX and \c centerY.
+
+    \section1 The main() Function
+
+    The application's multithreaded nature has no impact on its \c
+    main() function, which is as simple as usual:
+
+    \snippet threads/mandelbrot/main.cpp 0
+*/

examples/corelib/threads/doc/src/queuedcustomtype.qdoc

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+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example threads/queuedcustomtype
+    \title Queued Custom Type Example
+    \brief Demonstrates multi-thread programming using Qt.
+    \ingroup qtconcurrent-mtexamples
+
+    \brief The Queued Custom Type example shows how to send custom types between
+    threads with queued signals and slots.
+
+    \image queuedcustomtype-example.png
+
+    Contents:
+
+    \tableofcontents
+
+    \section1 Overview
+
+    In the \l{Custom Type Example}, we showed how to integrate custom types with
+    the meta-object system, enabling them to be stored in QVariant objects, written
+    out in debugging information and used in signal-slot communication.
+
+    In this example, we create a new value class, \c Block, and register it
+    with the meta-object system to enable us to send instances of it between
+    threads using queued signals and slots.
+
+    \section1 The Block Class
+
+    The \c Block class is similar to the \c Message class described in the
+    \l{Custom Type Example}. It provides the default constructor, copy
+    constructor and destructor in the public section of the class that the
+    meta-object system requires. It describes a colored rectangle.
+
+    \snippet threads/queuedcustomtype/block.h custom type definition and meta-type declaration
+
+    We will still need to register it with the meta-object system at
+    run-time by calling the qRegisterMetaType() template function before
+    we make any signal-slot connections that use this type.
+    Even though we do not intend to use the type with QVariant in this example,
+    it is good practice to also declare the new type with Q_DECLARE_METATYPE().
+
+    The implementation of the \c Block class is trivial, so we avoid quoting
+    it here.
+
+    \section1 The Window Class
+
+    We define a simple \c Window class with a public slot that accepts a
+    \c Block object. The rest of the class is concerned with managing the
+    user interface and handling images.
+
+    \snippet threads/queuedcustomtype/window.h Window class definition
+
+    The \c Window class also contains a worker thread, provided by a
+    \c RenderThread object. This will emit signals to send \c Block objects
+    to the window's \c addBlock(Block) slot.
+
+    The parts of the \c Window class that are most relevant are the constructor
+    and the \c addBlock(Block) slot.
+
+    The constructor creates a thread for rendering images, sets up a user
+    interface containing a label and two push buttons that are connected to
+    slots in the same class.
+
+    \snippet threads/queuedcustomtype/window.cpp Window constructor start
+    \snippet threads/queuedcustomtype/window.cpp set up widgets and connections
+    \snippet threads/queuedcustomtype/window.cpp connecting signal with custom type
+
+    In the last of these connections, we connect a signal in the
+    \c RenderThread object to the \c addBlock(Block) slot in the window.
+
+    \dots
+    \snippet threads/queuedcustomtype/window.cpp Window constructor finish
+
+    The rest of the constructor simply sets up the layout of the window.
+
+    The \c addBlock(Block) slot receives blocks from the rendering thread via
+    the signal-slot connection set up in the constructor:
+
+    \snippet threads/queuedcustomtype/window.cpp Adding blocks to the display
+
+    We simply paint these onto the label as they arrive.
+
+    \section1 The RenderThread Class
+
+    The \c RenderThread class processes an image, creating \c Block objects
+    and using the \c sendBlock(Block) signal to send them to other components
+    in the example.
+
+    \snippet threads/queuedcustomtype/renderthread.h RenderThread class definition
+
+    The constructor and destructor are not quoted here. These take care of
+    setting up the thread's internal state and cleaning up when it is destroyed.
+
+    Processing is started with the \c processImage() function, which calls the
+    \c RenderThread class's reimplementation of the QThread::run() function:
+
+    \snippet threads/queuedcustomtype/renderthread.cpp processing the image (start)
+
+    Ignoring the details of the way the image is processed, we see that the
+    signal containing a block is emitted in the usual way:
+
+    \dots
+    \snippet threads/queuedcustomtype/renderthread.cpp processing the image (finish)
+
+    Each signal that is emitted will be queued and delivered later to the
+    window's \c addBlock(Block) slot.
+
+    \section1 Registering the Type
+
+    In the example's \c{main()} function, we perform the registration of the
+    \c Block class as a custom type with the meta-object system by calling the
+    qRegisterMetaType() template function:
+
+    \snippet threads/queuedcustomtype/main.cpp main function
+
+    This call is placed here to ensure that the type is registered before any
+    signal-slot connections are made that use it.
+
+    The rest of the \c{main()} function is concerned with setting a seed for
+    the pseudo-random number generator, creating and showing the window, and
+    setting a default image. See the source code for the implementation of the
+    \c createImage() function.
+
+    \section1 Further Reading
+
+    This example showed how a custom type can be registered with the
+    meta-object system so that it can be used with signal-slot connections
+    between threads. For ordinary communication involving direct signals and
+    slots, it is enough to simply declare the type in the way described in the
+    \l{Custom Type Example}.
+
+    In practice, both the Q_DECLARE_METATYPE() macro and the qRegisterMetaType()
+    template function can be used to register custom types, but
+    qRegisterMetaType() is only required if you need to perform signal-slot
+    communication or need to create and destroy objects of the custom type
+    at run-time.
+
+    More information on using custom types with Qt can be found in the
+    \l{Creating Custom Qt Types} document.
+*/

examples/corelib/threads/doc/src/semaphores.qdoc

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+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example threads/semaphores
+    \title Semaphores Example
+    \brief Demonstrates multi-thread programming using Qt.
+    \ingroup qtconcurrent-mtexamples
+
+    \brief The Semaphores example shows how to use QSemaphore to control
+    access to a circular buffer shared by a producer thread and a
+    consumer thread.
+
+    The producer writes data to the buffer until it reaches the end
+    of the buffer, at which point it restarts from the beginning,
+    overwriting existing data. The consumer thread reads the data as
+    it is produced and writes it to standard error.
+
+    Semaphores make it possible to have a higher level of concurrency
+    than mutexes. If accesses to the buffer were guarded by a QMutex,
+    the consumer thread couldn't access the buffer at the same time
+    as the producer thread. Yet, there is no harm in having both
+    threads working on \e{different parts} of the buffer at the same
+    time.
+
+    The example comprises two classes: \c Producer and \c Consumer.
+    Both inherit from QThread. The circular buffer used for
+    communicating between these two classes and the semaphores that
+    protect it are global variables.
+
+    An alternative to using QSemaphore to solve the producer-consumer
+    problem is to use QWaitCondition and QMutex. This is what the
+    \l{Wait Conditions Example} does.
+
+    \section1 Global Variables
+
+    Let's start by reviewing the circular buffer and the associated
+    semaphores:
+
+    \snippet threads/semaphores/semaphores.cpp 0
+
+    \c DataSize is the amount of data that the producer will generate.
+    To keep the example as simple as possible, we make it a constant.
+    \c BufferSize is the size of the circular buffer. It is less than
+    \c DataSize, meaning that at some point the producer will reach
+    the end of the buffer and restart from the beginning.
+
+    To synchronize the producer and the consumer, we need two
+    semaphores. The \c freeBytes semaphore controls the "free" area
+    of the buffer (the area that the producer hasn't filled with data
+    yet or that the consumer has already read). The \c usedBytes
+    semaphore controls the "used" area of the buffer (the area that
+    the producer has filled but that the consumer hasn't read yet).
+
+    Together, the semaphores ensure that the producer is never more
+    than \c BufferSize bytes ahead of the consumer, and that the
+    consumer never reads data that the producer hasn't generated yet.
+
+    The \c freeBytes semaphore is initialized with \c BufferSize,
+    because initially the entire buffer is empty. The \c usedBytes
+    semaphore is initialized to 0 (the default value if none is
+    specified).
+
+    \section1 Producer Class
+
+    Let's review the code for the \c Producer class:
+
+    \snippet threads/semaphores/semaphores.cpp 1
+    \snippet threads/semaphores/semaphores.cpp 2
+
+    The producer generates \c DataSize bytes of data. Before it
+    writes a byte to the circular buffer, it must acquire a "free"
+    byte using the \c freeBytes semaphore. The QSemaphore::acquire()
+    call might block if the consumer hasn't kept up the pace with the
+    producer.
+
+    At the end, the producer releases a byte using the \c usedBytes
+    semaphore. The "free" byte has successfully been transformed into
+    a "used" byte, ready to be read by the consumer.
+
+    \section1 Consumer Class
+
+    Let's now turn to the \c Consumer class:
+
+    \snippet threads/semaphores/semaphores.cpp 3
+    \snippet threads/semaphores/semaphores.cpp 4
+
+    The code is very similar to the producer, except that this time
+    we acquire a "used" byte and release a "free" byte, instead of
+    the opposite.
+
+    \section1 The main() Function
+
+    In \c main(), we create the two threads and call QThread::wait()
+    to ensure that both threads get time to finish before we exit:
+
+    \snippet threads/semaphores/semaphores.cpp 5
+    \snippet threads/semaphores/semaphores.cpp 6
+
+    So what happens when we run the program? Initially, the producer
+    thread is the only one that can do anything; the consumer is
+    blocked waiting for the \c usedBytes semaphore to be released (its
+    initial \l{QSemaphore::available()}{available()} count is 0).
+    Once the producer has put one byte in the buffer,
+    \c{freeBytes.available()} is \c BufferSize - 1 and
+    \c{usedBytes.available()} is 1. At that point, two things can
+    happen: Either the consumer thread takes over and reads that
+    byte, or the producer thread gets to produce a second byte.
+
+    The producer-consumer model presented in this example makes it
+    possible to write highly concurrent multithreaded applications.
+    On a multiprocessor machine, the program is potentially up to
+    twice as fast as the equivalent mutex-based program, since the
+    two threads can be active at the same time on different parts of
+    the buffer.
+
+    Be aware though that these benefits aren't always realized.
+    Acquiring and releasing a QSemaphore has a cost. In practice, it
+    would probably be worthwhile to divide the buffer into chunks and
+    to operate on chunks instead of individual bytes. The buffer size
+    is also a parameter that must be selected carefully, based on
+    experimentation.
+*/

examples/corelib/threads/doc/src/waitconditions.qdoc

@@ -0,0 +1,130 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example threads/waitconditions
+    \title Wait Conditions Example
+    \brief Demonstrates multi-thread programming using Qt.
+    \ingroup qtconcurrent-mtexamples
+
+    \brief The Wait Conditions example shows how to use QWaitCondition and
+    QMutex to control access to a circular buffer shared by a
+    producer thread and a consumer thread.
+
+    The producer writes data to the buffer until it reaches the end
+    of the buffer, at which point it restarts from the beginning,
+    overwriting existing data. The consumer thread reads the data as
+    it is produced and writes it to standard error.
+
+    Wait conditions make it possible to have a higher level of
+    concurrency than what is possible with mutexes alone. If accesses
+    to the buffer were simply guarded by a QMutex, the consumer
+    thread couldn't access the buffer at the same time as the
+    producer thread. Yet, there is no harm in having both threads
+    working on \e{different parts} of the buffer at the same time.
+
+    The example comprises two classes: \c Producer and \c Consumer.
+    Both inherit from QThread. The circular buffer used for
+    communicating between these two classes and the synchronization
+    tools that protect it are global variables.
+
+    An alternative to using QWaitCondition and QMutex to solve the
+    producer-consumer problem is to use QSemaphore. This is what the
+    \l{Semaphores Example} does.
+
+    \section1 Global Variables
+
+    Let's start by reviewing the circular buffer and the associated
+    synchronization tools:
+
+    \snippet threads/waitconditions/waitconditions.cpp 0
+
+    \c DataSize is the amount of data that the producer will generate.
+    To keep the example as simple as possible, we make it a constant.
+    \c BufferSize is the size of the circular buffer. It is less than
+    \c DataSize, meaning that at some point the producer will reach
+    the end of the buffer and restart from the beginning.
+
+    To synchronize the producer and the consumer, we need two wait
+    conditions and one mutex. The \c bufferNotEmpty condition is
+    signalled when the producer has generated some data, telling the
+    consumer that it can start reading it. The \c bufferNotFull
+    condition is signalled when the consumer has read some data,
+    telling the producer that it can generate more. The \c numUsedBytes
+    is the number of bytes in the buffer that contain data.
+
+    Together, the wait conditions, the mutex, and the \c numUsedBytes
+    counter ensure that the producer is never more than \c BufferSize
+    bytes ahead of the consumer, and that the consumer never reads
+    data that the producer hasn't generated yet.
+
+    \section1 Producer Class
+
+    Let's review the code for the \c Producer class:
+
+    \snippet threads/waitconditions/waitconditions.cpp 1
+    \snippet threads/waitconditions/waitconditions.cpp 2
+
+    The producer generates \c DataSize bytes of data. Before it
+    writes a byte to the circular buffer, it must first check whether
+    the buffer is full (i.e., \c numUsedBytes equals \c BufferSize).
+    If the buffer is full, the thread waits on the \c bufferNotFull
+    condition.
+
+    At the end, the producer increments \c numUsedBytes and signalls
+    that the condition \c bufferNotEmpty is true, since \c
+    numUsedBytes is necessarily greater than 0.
+
+    We guard all accesses to the \c numUsedBytes variable with a
+    mutex. In addition, the QWaitCondition::wait() function accepts a
+    mutex as its argument. This mutex is unlocked before the thread
+    is put to sleep and locked when the thread wakes up. Furthermore,
+    the transition from the locked state to the wait state is atomic,
+    to prevent race conditions from occurring.
+
+    \section1 Consumer Class
+
+    Let's turn to the \c Consumer class:
+
+    \snippet threads/waitconditions/waitconditions.cpp 3
+    \snippet threads/waitconditions/waitconditions.cpp 4
+
+    The code is very similar to the producer. Before we read the
+    byte, we check whether the buffer is empty (\c numUsedBytes is 0)
+    instead of whether it's full and wait on the \c bufferNotEmpty
+    condition if it's empty. After we've read the byte, we decrement
+    \c numUsedBytes (instead of incrementing it), and we signal the
+    \c bufferNotFull condition (instead of the \c bufferNotEmpty
+    condition).
+
+    \section1 The main() Function
+
+    In \c main(), we create the two threads and call QThread::wait()
+    to ensure that both threads get time to finish before we exit:
+
+    \snippet threads/waitconditions/waitconditions.cpp 5
+    \snippet threads/waitconditions/waitconditions.cpp 6
+
+    So what happens when we run the program? Initially, the producer
+    thread is the only one that can do anything; the consumer is
+    blocked waiting for the \c bufferNotEmpty condition to be
+    signalled (\c numUsedBytes is 0). Once the producer has put one
+    byte in the buffer, \c numUsedBytes is strictly greater than 0, and the
+    \c bufferNotEmpty condition is signalled. At that point, two
+    things can happen: Either the consumer thread takes over and
+    reads that byte, or the producer gets to produce a second byte.
+
+    The producer-consumer model presented in this example makes it
+    possible to write highly concurrent multithreaded applications.
+    On a multiprocessor machine, the program is potentially up to
+    twice as fast as the equivalent mutex-based program, since the
+    two threads can be active at the same time on different parts of
+    the buffer.
+
+    Be aware though that these benefits aren't always realized.
+    Locking and unlocking a QMutex has a cost. In practice, it would
+    probably be worthwhile to divide the buffer into chunks and to
+    operate on chunks instead of individual bytes. The buffer size is
+    also a parameter that must be selected carefully, based on
+    experimentation.
+*/

examples/corelib/threads/mandelbrot/CMakeLists.txt

@@ -0,0 +1,38 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(mandelbrot LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/threads/mandelbrot")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
+
+qt_standard_project_setup()
+
+qt_add_executable(mandelbrot
+    main.cpp
+    mandelbrotwidget.cpp mandelbrotwidget.h
+    renderthread.cpp renderthread.h
+)
+
+set_target_properties(mandelbrot PROPERTIES
+    WIN32_EXECUTABLE TRUE
+    MACOSX_BUNDLE TRUE
+)
+
+target_link_libraries(mandelbrot PRIVATE
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Widgets
+)
+
+install(TARGETS mandelbrot
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/threads/mandelbrot/main.cpp

@@ -0,0 +1,44 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "mandelbrotwidget.h"
+
+#include <QApplication>
+
+#include <QScreen>
+
+#include <QCommandLineParser>
+#include <QCommandLineOption>
+#include <QDebug>
+#include <QRect>
+
+//! [0]
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+
+    QCommandLineParser parser;
+    parser.setApplicationDescription("Qt Mandelbrot Example");
+    parser.addHelpOption();
+    parser.addVersionOption();
+    QCommandLineOption passesOption("passes", "Number of passes (1-8)", "passes");
+    parser.addOption(passesOption);
+    parser.process(app);
+
+    if (parser.isSet(passesOption)) {
+        const auto passesStr = parser.value(passesOption);
+        bool ok;
+        const int passes = passesStr.toInt(&ok);
+        if (!ok || passes < 1 || passes > 8) {
+            qWarning() << "Invalid value:" << passesStr;
+            return -1;
+        }
+        RenderThread::setNumPasses(passes);
+    }
+
+    MandelbrotWidget widget;
+    widget.grabGesture(Qt::PinchGesture);
+    widget.show();
+    return app.exec();
+}
+//! [0]

examples/corelib/threads/mandelbrot/mandelbrot.pro

@@ -0,0 +1,11 @@
+QT += widgets
+
+HEADERS       = mandelbrotwidget.h \
+                renderthread.h
+SOURCES       = main.cpp \
+                mandelbrotwidget.cpp \
+                renderthread.cpp
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/threads/mandelbrot
+INSTALLS += target

examples/corelib/threads/mandelbrot/mandelbrotwidget.cpp

@@ -0,0 +1,248 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "mandelbrotwidget.h"
+
+#include <QGesture>
+#include <QKeyEvent>
+#include <QPainter>
+
+#include <math.h>
+
+//! [0]
+const double DefaultCenterX = -0.637011;
+const double DefaultCenterY = -0.0395159;
+const double DefaultScale = 0.00403897;
+
+const double ZoomInFactor = 0.8;
+const double ZoomOutFactor = 1 / ZoomInFactor;
+const int ScrollStep = 20;
+//! [0]
+
+//! [1]
+MandelbrotWidget::MandelbrotWidget(QWidget *parent) :
+    QWidget(parent),
+    centerX(DefaultCenterX),
+    centerY(DefaultCenterY),
+    pixmapScale(DefaultScale),
+    curScale(DefaultScale)
+{
+    help = tr("Zoom with mouse wheel, +/- keys or pinch.  Scroll with arrow keys or by dragging.");
+    connect(&thread, &RenderThread::renderedImage,
+            this, &MandelbrotWidget::updatePixmap);
+
+    setWindowTitle(tr("Mandelbrot"));
+#if QT_CONFIG(cursor)
+    setCursor(Qt::CrossCursor);
+#endif
+}
+//! [1]
+
+//! [2]
+void MandelbrotWidget::paintEvent(QPaintEvent * /* event */)
+{
+    QPainter painter(this);
+    painter.fillRect(rect(), Qt::black);
+
+    if (pixmap.isNull()) {
+        painter.setPen(Qt::white);
+        painter.drawText(rect(), Qt::AlignCenter|Qt::TextWordWrap, tr("Rendering initial image, please wait..."));
+//! [2] //! [3]
+        return;
+//! [3] //! [4]
+    }
+//! [4]
+
+//! [5]
+    if (qFuzzyCompare(curScale, pixmapScale)) {
+//! [5] //! [6]
+        painter.drawPixmap(pixmapOffset, pixmap);
+//! [6] //! [7]
+    } else {
+//! [7] //! [8]
+        auto previewPixmap = qFuzzyCompare(pixmap.devicePixelRatio(), qreal(1))
+            ? pixmap
+            : pixmap.scaled(pixmap.deviceIndependentSize().toSize(), Qt::KeepAspectRatio,
+                            Qt::SmoothTransformation);
+        double scaleFactor = pixmapScale / curScale;
+        int newWidth = int(previewPixmap.width() * scaleFactor);
+        int newHeight = int(previewPixmap.height() * scaleFactor);
+        int newX = pixmapOffset.x() + (previewPixmap.width() - newWidth) / 2;
+        int newY = pixmapOffset.y() + (previewPixmap.height() - newHeight) / 2;
+
+        painter.save();
+        painter.translate(newX, newY);
+        painter.scale(scaleFactor, scaleFactor);
+
+        QRectF exposed = painter.transform().inverted().mapRect(rect()).adjusted(-1, -1, 1, 1);
+        painter.drawPixmap(exposed, previewPixmap, exposed);
+        painter.restore();
+    }
+//! [8] //! [9]
+
+    QFontMetrics metrics = painter.fontMetrics();
+    if (!info.isEmpty()){
+        int infoWidth = metrics.horizontalAdvance(info);
+        int infoHeight = metrics.height();
+
+        painter.setPen(Qt::NoPen);
+        painter.setBrush(QColor(0, 0, 0, 127));
+        infoHeight = (infoWidth/width()+1) * (infoHeight + 5);
+        painter.drawRect((width() - infoWidth) / 2 - 5, 0, infoWidth + 10, infoHeight);
+
+        painter.setPen(Qt::white);
+        painter.drawText(rect(), Qt::AlignHCenter|Qt::AlignTop|Qt::TextWordWrap, info);
+    }
+
+    int helpWidth = metrics.horizontalAdvance(help);
+    int helpHeight = metrics.height();
+
+    painter.setPen(Qt::NoPen);
+    painter.setBrush(QColor(0, 0, 0, 127));
+    helpHeight = (helpWidth/width()+1) * (helpHeight + 5);
+    painter.drawRect((width() - helpWidth) / 2 - 5, height()-helpHeight, helpWidth + 10, helpHeight);
+
+    painter.setPen(Qt::white);
+    painter.drawText(rect(), Qt::AlignHCenter|Qt::AlignBottom|Qt::TextWordWrap, help);
+
+}
+//! [9]
+
+//! [10]
+void MandelbrotWidget::resizeEvent(QResizeEvent * /* event */)
+{
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatio());
+}
+//! [10]
+
+//! [11]
+void MandelbrotWidget::keyPressEvent(QKeyEvent *event)
+{
+    switch (event->key()) {
+    case Qt::Key_Plus:
+        zoom(ZoomInFactor);
+        break;
+    case Qt::Key_Minus:
+        zoom(ZoomOutFactor);
+        break;
+    case Qt::Key_Left:
+        scroll(-ScrollStep, 0);
+        break;
+    case Qt::Key_Right:
+        scroll(+ScrollStep, 0);
+        break;
+    case Qt::Key_Down:
+        scroll(0, -ScrollStep);
+        break;
+    case Qt::Key_Up:
+        scroll(0, +ScrollStep);
+        break;
+    case Qt::Key_Q:
+        close();
+        break;
+    default:
+        QWidget::keyPressEvent(event);
+    }
+}
+//! [11]
+
+#if QT_CONFIG(wheelevent)
+//! [12]
+void MandelbrotWidget::wheelEvent(QWheelEvent *event)
+{
+    const int numDegrees = event->angleDelta().y() / 8;
+    const double numSteps = numDegrees / double(15);
+    zoom(pow(ZoomInFactor, numSteps));
+}
+//! [12]
+#endif
+
+//! [13]
+void MandelbrotWidget::mousePressEvent(QMouseEvent *event)
+{
+    if (event->button() == Qt::LeftButton)
+        lastDragPos = event->position().toPoint();
+}
+//! [13]
+
+//! [14]
+void MandelbrotWidget::mouseMoveEvent(QMouseEvent *event)
+{
+    if (event->buttons() & Qt::LeftButton) {
+        pixmapOffset += event->position().toPoint() - lastDragPos;
+        lastDragPos = event->position().toPoint();
+        update();
+    }
+}
+//! [14]
+
+//! [15]
+void MandelbrotWidget::mouseReleaseEvent(QMouseEvent *event)
+{
+    if (event->button() == Qt::LeftButton) {
+        pixmapOffset += event->position().toPoint() - lastDragPos;
+        lastDragPos = QPoint();
+
+        const auto pixmapSize = pixmap.deviceIndependentSize().toSize();
+        int deltaX = (width() - pixmapSize.width()) / 2 - pixmapOffset.x();
+        int deltaY = (height() - pixmapSize.height()) / 2 - pixmapOffset.y();
+        scroll(deltaX, deltaY);
+    }
+}
+//! [15]
+
+//! [16]
+void MandelbrotWidget::updatePixmap(const QImage &image, double scaleFactor)
+{
+    if (!lastDragPos.isNull())
+        return;
+
+    info = image.text(RenderThread::infoKey());
+
+    pixmap = QPixmap::fromImage(image);
+    pixmapOffset = QPoint();
+    lastDragPos = QPoint();
+    pixmapScale = scaleFactor;
+    update();
+}
+//! [16]
+
+//! [17]
+void MandelbrotWidget::zoom(double zoomFactor)
+{
+    curScale *= zoomFactor;
+    update();
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatio());
+}
+//! [17]
+
+//! [18]
+void MandelbrotWidget::scroll(int deltaX, int deltaY)
+{
+    centerX += deltaX * curScale;
+    centerY += deltaY * curScale;
+    update();
+    thread.render(centerX, centerY, curScale, size(), devicePixelRatio());
+}
+//! [18]
+
+//! [gesture1]
+#ifndef QT_NO_GESTURES
+bool MandelbrotWidget::gestureEvent(QGestureEvent *event)
+{
+    if (auto *pinch = static_cast<QPinchGesture *>(event->gesture(Qt::PinchGesture))) {
+        if (pinch->changeFlags().testFlag(QPinchGesture::ScaleFactorChanged))
+            zoom(1.0 / pinch->scaleFactor());
+        return true;
+    }
+    return false;
+}
+
+bool MandelbrotWidget::event(QEvent *event)
+{
+    if (event->type() == QEvent::Gesture)
+        return gestureEvent(static_cast<QGestureEvent*>(event));
+    return QWidget::event(event);
+}
+#endif
+//! [gesture1]

examples/corelib/threads/mandelbrot/mandelbrotwidget.h

@@ -0,0 +1,59 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef MANDELBROTWIDGET_H
+#define MANDELBROTWIDGET_H
+
+#include <QGestureEvent>
+#include <QPixmap>
+#include <QWidget>
+#include "renderthread.h"
+
+
+//! [0]
+class MandelbrotWidget : public QWidget
+{
+    Q_OBJECT
+
+public:
+    MandelbrotWidget(QWidget *parent = nullptr);
+
+protected:
+    QSize sizeHint() const override { return {1024, 768}; };
+    void paintEvent(QPaintEvent *event) override;
+    void resizeEvent(QResizeEvent *event) override;
+    void keyPressEvent(QKeyEvent *event) override;
+#if QT_CONFIG(wheelevent)
+    void wheelEvent(QWheelEvent *event) override;
+#endif
+    void mousePressEvent(QMouseEvent *event) override;
+    void mouseMoveEvent(QMouseEvent *event) override;
+    void mouseReleaseEvent(QMouseEvent *event) override;
+#ifndef QT_NO_GESTURES
+    bool event(QEvent *event) override;
+#endif
+
+private slots:
+    void updatePixmap(const QImage &image, double scaleFactor);
+    void zoom(double zoomFactor);
+
+private:
+    void scroll(int deltaX, int deltaY);
+#ifndef QT_NO_GESTURES
+    bool gestureEvent(QGestureEvent *event);
+#endif
+
+    RenderThread thread;
+    QPixmap pixmap;
+    QPoint pixmapOffset;
+    QPoint lastDragPos;
+    QString help;
+    QString info;
+    double centerX;
+    double centerY;
+    double pixmapScale;
+    double curScale;
+};
+//! [0]
+
+#endif // MANDELBROTWIDGET_H

examples/corelib/threads/mandelbrot/renderthread.cpp

@@ -0,0 +1,198 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "renderthread.h"
+
+#include <QImage>
+
+#include <QElapsedTimer>
+#include <QTextStream>
+
+#include <cmath>
+
+int RenderThread::numPasses = 8;
+
+//! [0]
+RenderThread::RenderThread(QObject *parent)
+    : QThread(parent)
+{
+    for (int i = 0; i < ColormapSize; ++i)
+        colormap[i] = rgbFromWaveLength(380.0 + (i * 400.0 / ColormapSize));
+}
+//! [0]
+
+//! [1]
+RenderThread::~RenderThread()
+{
+    mutex.lock();
+    abort = true;
+    condition.wakeOne();
+    mutex.unlock();
+
+    wait();
+}
+//! [1]
+
+//! [2]
+void RenderThread::render(double centerX, double centerY, double scaleFactor,
+                          QSize resultSize, double devicePixelRatio)
+{
+    QMutexLocker locker(&mutex);
+
+    this->centerX = centerX;
+    this->centerY = centerY;
+    this->scaleFactor = scaleFactor;
+    this->devicePixelRatio = devicePixelRatio;
+    this->resultSize = resultSize;
+
+    if (!isRunning()) {
+        start(LowPriority);
+    } else {
+        restart = true;
+        condition.wakeOne();
+    }
+}
+//! [2]
+
+//! [3]
+void RenderThread::run()
+{
+    QElapsedTimer timer;
+    forever {
+        mutex.lock();
+        const double devicePixelRatio = this->devicePixelRatio;
+        const QSize resultSize = this->resultSize * devicePixelRatio;
+        const double requestedScaleFactor = this->scaleFactor;
+        const double scaleFactor = requestedScaleFactor / devicePixelRatio;
+        const double centerX = this->centerX;
+        const double centerY = this->centerY;
+        mutex.unlock();
+//! [3]
+
+//! [4]
+        int halfWidth = resultSize.width() / 2;
+//! [4] //! [5]
+        int halfHeight = resultSize.height() / 2;
+        QImage image(resultSize, QImage::Format_RGB32);
+        image.setDevicePixelRatio(devicePixelRatio);
+
+        int pass = 0;
+        while (pass < numPasses) {
+            const int MaxIterations = (1 << (2 * pass + 6)) + 32;
+            const int Limit = 4;
+            bool allBlack = true;
+
+            timer.restart();
+
+            for (int y = -halfHeight; y < halfHeight; ++y) {
+                if (restart)
+                    break;
+                if (abort)
+                    return;
+
+                auto scanLine =
+                        reinterpret_cast<uint *>(image.scanLine(y + halfHeight));
+                const double ay = centerY + (y * scaleFactor);
+
+                for (int x = -halfWidth; x < halfWidth; ++x) {
+                    const double ax = centerX + (x * scaleFactor);
+                    double a1 = ax;
+                    double b1 = ay;
+                    int numIterations = 0;
+
+                    do {
+                        ++numIterations;
+                        const double a2 = (a1 * a1) - (b1 * b1) + ax;
+                        const double b2 = (2 * a1 * b1) + ay;
+                        if ((a2 * a2) + (b2 * b2) > Limit)
+                            break;
+
+                        ++numIterations;
+                        a1 = (a2 * a2) - (b2 * b2) + ax;
+                        b1 = (2 * a2 * b2) + ay;
+                        if ((a1 * a1) + (b1 * b1) > Limit)
+                            break;
+                    } while (numIterations < MaxIterations);
+
+                    if (numIterations < MaxIterations) {
+                        *scanLine++ = colormap[numIterations % ColormapSize];
+                        allBlack = false;
+                    } else {
+                        *scanLine++ = qRgb(0, 0, 0);
+                    }
+                }
+            }
+
+            if (allBlack && pass == 0) {
+                pass = 4;
+            } else {
+                if (!restart) {
+                    QString message;
+                    QTextStream str(&message);
+                    str << " Pass " << (pass + 1) << '/' << numPasses
+                        << ", max iterations: " << MaxIterations << ", time: ";
+                    const auto elapsed = timer.elapsed();
+                    if (elapsed > 2000)
+                        str << (elapsed / 1000) << 's';
+                    else
+                        str << elapsed << "ms";
+                    image.setText(infoKey(), message);
+
+                    emit renderedImage(image, requestedScaleFactor);
+                }
+//! [5] //! [6]
+                ++pass;
+            }
+//! [6] //! [7]
+        }
+//! [7]
+
+//! [8]
+        mutex.lock();
+//! [8] //! [9]
+        if (!restart)
+            condition.wait(&mutex);
+        restart = false;
+        mutex.unlock();
+    }
+}
+//! [9]
+
+//! [10]
+uint RenderThread::rgbFromWaveLength(double wave)
+{
+    double r = 0;
+    double g = 0;
+    double b = 0;
+
+    if (wave >= 380.0 && wave <= 440.0) {
+        r = -1.0 * (wave - 440.0) / (440.0 - 380.0);
+        b = 1.0;
+    } else if (wave >= 440.0 && wave <= 490.0) {
+        g = (wave - 440.0) / (490.0 - 440.0);
+        b = 1.0;
+    } else if (wave >= 490.0 && wave <= 510.0) {
+        g = 1.0;
+        b = -1.0 * (wave - 510.0) / (510.0 - 490.0);
+    } else if (wave >= 510.0 && wave <= 580.0) {
+        r = (wave - 510.0) / (580.0 - 510.0);
+        g = 1.0;
+    } else if (wave >= 580.0 && wave <= 645.0) {
+        r = 1.0;
+        g = -1.0 * (wave - 645.0) / (645.0 - 580.0);
+    } else if (wave >= 645.0 && wave <= 780.0) {
+        r = 1.0;
+    }
+
+    double s = 1.0;
+    if (wave > 700.0)
+        s = 0.3 + 0.7 * (780.0 - wave) / (780.0 - 700.0);
+    else if (wave <  420.0)
+        s = 0.3 + 0.7 * (wave - 380.0) / (420.0 - 380.0);
+
+    r = std::pow(r * s, 0.8);
+    g = std::pow(g * s, 0.8);
+    b = std::pow(b * s, 0.8);
+    return qRgb(int(r * 255), int(g * 255), int(b * 255));
+}
+//! [10]

examples/corelib/threads/mandelbrot/renderthread.h

@@ -0,0 +1,57 @@
+// Copyright (C) 2021 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef RENDERTHREAD_H
+#define RENDERTHREAD_H
+
+#include <QMutex>
+#include <QSize>
+#include <QThread>
+#include <QWaitCondition>
+
+QT_BEGIN_NAMESPACE
+class QImage;
+QT_END_NAMESPACE
+
+//! [0]
+class RenderThread : public QThread
+{
+    Q_OBJECT
+
+public:
+    RenderThread(QObject *parent = nullptr);
+    ~RenderThread();
+
+    void render(double centerX, double centerY, double scaleFactor, QSize resultSize,
+                double devicePixelRatio);
+
+    static void setNumPasses(int n) { numPasses = n; }
+
+    static QString infoKey() { return QStringLiteral("info"); }
+
+signals:
+    void renderedImage(const QImage &image, double scaleFactor);
+
+protected:
+    void run() override;
+
+private:
+    static uint rgbFromWaveLength(double wave);
+
+    QMutex mutex;
+    QWaitCondition condition;
+    double centerX;
+    double centerY;
+    double scaleFactor;
+    double devicePixelRatio;
+    QSize resultSize;
+    static int numPasses;
+    bool restart = false;
+    bool abort = false;
+
+    enum { ColormapSize = 512 };
+    uint colormap[ColormapSize];
+};
+//! [0]
+
+#endif // RENDERTHREAD_H

examples/corelib/threads/queuedcustomtype/CMakeLists.txt

@@ -0,0 +1,39 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(queuedcustomtype LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/threads/queuedcustomtype")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets)
+
+qt_standard_project_setup()
+
+qt_add_executable(queuedcustomtype
+    block.cpp block.h
+    main.cpp
+    renderthread.cpp renderthread.h
+    window.cpp window.h
+)
+
+set_target_properties(queuedcustomtype PROPERTIES
+    WIN32_EXECUTABLE TRUE
+    MACOSX_BUNDLE TRUE
+)
+
+target_link_libraries(queuedcustomtype PRIVATE
+    Qt6::Core
+    Qt6::Gui
+    Qt6::Widgets
+)
+
+install(TARGETS queuedcustomtype
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/threads/queuedcustomtype/block.cpp

@@ -0,0 +1,32 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "block.h"
+
+Block::Block()
+{
+}
+
+Block::Block(const Block &other)
+    : m_rect(other.m_rect), m_color(other.m_color)
+{
+}
+
+Block::~Block()
+{
+}
+
+Block::Block(const QRect &rect, const QColor &color)
+    : m_rect(rect), m_color(color)
+{
+}
+
+QColor Block::color() const
+{
+    return m_color;
+}
+
+QRect Block::rect() const
+{
+    return m_rect;
+}

examples/corelib/threads/queuedcustomtype/block.h

@@ -0,0 +1,32 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef BLOCK_H
+#define BLOCK_H
+
+#include <QColor>
+#include <QMetaType>
+#include <QRect>
+
+//! [custom type definition and meta-type declaration]
+class Block
+{
+public:
+    Block();
+    Block(const Block &other);
+    ~Block();
+
+    Block(const QRect &rect, const QColor &color);
+
+    QColor color() const;
+    QRect rect() const;
+
+private:
+    QRect m_rect;
+    QColor m_color;
+};
+
+Q_DECLARE_METATYPE(Block);
+//! [custom type definition and meta-type declaration]
+
+#endif

examples/corelib/threads/queuedcustomtype/main.cpp

@@ -0,0 +1,90 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QApplication>
+#include <QPainter>
+#include <QTime>
+#include "block.h"
+#include "window.h"
+
+QImage createImage(int width, int height)
+{
+    QImage image(width, height, QImage::Format_RGB16);
+    QPainter painter;
+    QPen pen;
+    pen.setStyle(Qt::NoPen);
+    QBrush brush(Qt::blue);
+
+    painter.begin(&image);
+    painter.fillRect(image.rect(), brush);
+    brush.setColor(Qt::white);
+    painter.setPen(pen);
+    painter.setBrush(brush);
+
+    static const QPointF points1[3] = {
+        QPointF(4, 4),
+        QPointF(7, 4),
+        QPointF(5.5, 1)
+    };
+
+    static const QPointF points2[3] = {
+        QPointF(1, 4),
+        QPointF(7, 4),
+        QPointF(10, 10)
+    };
+
+    static const QPointF points3[3] = {
+        QPointF(4, 4),
+        QPointF(10, 4),
+        QPointF(1, 10)
+    };
+
+    painter.setWindow(0, 0, 10, 10);
+
+    int x = 0;
+    int y = 0;
+    int starWidth = image.width()/3;
+    int starHeight = image.height()/3;
+
+    QRect rect(x, y, starWidth, starHeight);
+
+    for (int i = 0; i < 9; ++i) {
+
+        painter.setViewport(rect);
+        painter.drawPolygon(points1, 3);
+        painter.drawPolygon(points2, 3);
+        painter.drawPolygon(points3, 3);
+
+        if (i % 3 == 2) {
+            y = y + starHeight;
+            rect.moveTop(y);
+
+            x = 0;
+            rect.moveLeft(x);
+
+        } else {
+            x = x + starWidth;
+            rect.moveLeft(x);
+        }
+    }
+
+    painter.end();
+    return image;
+}
+
+//! [main function] //! [main start]
+int main(int argc, char *argv[])
+{
+    QApplication app(argc, argv);
+//! [main start] //! [register meta-type for queued communications]
+    qRegisterMetaType<Block>();
+//! [register meta-type for queued communications]
+
+    Window window;
+    window.show();
+
+    window.loadImage(createImage(256, 256));
+//! [main finish]
+    return app.exec();
+}
+//! [main finish] //! [main function]

examples/corelib/threads/queuedcustomtype/queuedcustomtype.pro

@@ -0,0 +1,15 @@
+HEADERS   = block.h \
+            renderthread.h \
+            window.h
+SOURCES   = main.cpp \
+            block.cpp \
+            renderthread.cpp \
+            window.cpp
+QT += widgets
+requires(qtConfig(filedialog))
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/threads/queuedcustomtype
+INSTALLS += target
+
+

examples/corelib/threads/queuedcustomtype/renderthread.cpp

@@ -0,0 +1,74 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "renderthread.h"
+
+#include <QRandomGenerator>
+
+RenderThread::RenderThread(QObject *parent)
+    : QThread(parent)
+{
+    m_abort = false;
+}
+
+RenderThread::~RenderThread()
+{
+    mutex.lock();
+    m_abort = true;
+    mutex.unlock();
+
+    wait();
+}
+
+//![processing the image (start)]
+void RenderThread::processImage(const QImage &image)
+{
+    if (image.isNull())
+        return;
+
+    m_image = image;
+    m_abort = false;
+    start();
+}
+
+void RenderThread::run()
+{
+    int size = qMax(m_image.width()/20, m_image.height()/20);
+    for (int s = size; s > 0; --s) {
+        for (int c = 0; c < 400; ++c) {
+//![processing the image (start)]
+            int x1 = qMax(0, QRandomGenerator::global()->bounded(m_image.width()) - s/2);
+            int x2 = qMin(x1 + s/2 + 1, m_image.width());
+            int y1 = qMax(0, QRandomGenerator::global()->bounded(m_image.height()) - s/2);
+            int y2 = qMin(y1 + s/2 + 1, m_image.height());
+            int n = 0;
+            int red = 0;
+            int green = 0;
+            int blue = 0;
+            for (int i = y1; i < y2; ++i) {
+                for (int j = x1; j < x2; ++j) {
+                    QRgb pixel = m_image.pixel(j, i);
+                    red += qRed(pixel);
+                    green += qGreen(pixel);
+                    blue += qBlue(pixel);
+                    n += 1;
+                }
+            }
+//![processing the image (finish)]
+            Block block(QRect(x1, y1, x2 - x1 + 1, y2 - y1 + 1),
+                        QColor(red/n, green/n, blue/n));
+            emit sendBlock(block);
+            if (m_abort)
+                return;
+            msleep(10);
+        }
+    }
+}
+//![processing the image (finish)]
+
+void RenderThread::stopProcess()
+{
+    mutex.lock();
+    m_abort = true;
+    mutex.unlock();
+}

examples/corelib/threads/queuedcustomtype/renderthread.h

@@ -0,0 +1,39 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef RENDERTHREAD_H
+#define RENDERTHREAD_H
+
+#include <QImage>
+#include <QMutex>
+#include <QThread>
+#include "block.h"
+
+//! [RenderThread class definition]
+class RenderThread : public QThread
+{
+    Q_OBJECT
+
+public:
+    RenderThread(QObject *parent = nullptr);
+    ~RenderThread();
+
+    void processImage(const QImage &image);
+
+signals:
+    void sendBlock(const Block &block);
+
+public slots:
+    void stopProcess();
+
+protected:
+    void run();
+
+private:
+    bool m_abort;
+    QImage m_image;
+    QMutex mutex;
+};
+//! [RenderThread class definition]
+
+#endif

examples/corelib/threads/queuedcustomtype/window.cpp

@@ -0,0 +1,103 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "window.h"
+#include <QtWidgets>
+
+//! [Window constructor start]
+Window::Window(QWidget *parent)
+    : QWidget(parent), thread(new RenderThread(this))
+{
+//! [Window constructor start] //! [set up widgets and connections]
+
+    label = new QLabel(this);
+    label->setAlignment(Qt::AlignCenter);
+
+    loadButton = new QPushButton(tr("&Load image..."), this);
+    resetButton = new QPushButton(tr("&Stop"), this);
+    resetButton->setEnabled(false);
+
+    connect(loadButton, &QPushButton::clicked,
+            this, QOverload<>::of(&Window::loadImage));
+    connect(resetButton, &QPushButton::clicked,
+            thread, &RenderThread::stopProcess);
+    connect(thread, &RenderThread::finished,
+            this, &Window::resetUi);
+//! [set up widgets and connections] //! [connecting signal with custom type]
+    connect(thread, &RenderThread::sendBlock,
+            this, &Window::addBlock);
+//! [connecting signal with custom type]
+
+    QHBoxLayout *buttonLayout = new QHBoxLayout;
+    buttonLayout->addStretch();
+    buttonLayout->addWidget(loadButton);
+    buttonLayout->addWidget(resetButton);
+    buttonLayout->addStretch();
+
+    QVBoxLayout *layout = new QVBoxLayout(this);
+    layout->addWidget(label);
+    layout->addLayout(buttonLayout);
+
+//! [Window constructor finish]
+    setWindowTitle(tr("Queued Custom Type"));
+}
+//! [Window constructor finish]
+
+void Window::loadImage()
+{
+    QStringList formats;
+    const QList<QByteArray> supportedFormats = QImageReader::supportedImageFormats();
+    for (const QByteArray &format : supportedFormats)
+        if (format.toLower() == format)
+            formats.append(QLatin1String("*.") + QString::fromLatin1(format));
+
+    QString newPath = QFileDialog::getOpenFileName(this, tr("Open Image"),
+        path, tr("Image files (%1)").arg(formats.join(' ')));
+
+    if (newPath.isEmpty())
+        return;
+
+    QImage image(newPath);
+    if (!image.isNull()) {
+        loadImage(image);
+        path = newPath;
+    }
+}
+
+void Window::loadImage(const QImage &image)
+{
+    QImage useImage;
+    QRect space = QGuiApplication::primaryScreen()->availableGeometry();
+    if (image.width() > 0.75*space.width() || image.height() > 0.75*space.height())
+        useImage = image.scaled(0.75*space.width(), 0.75*space.height(),
+                                Qt::KeepAspectRatio, Qt::SmoothTransformation);
+    else
+        useImage = image;
+
+    pixmap = QPixmap(useImage.width(), useImage.height());
+    pixmap.fill(qRgb(255, 255, 255));
+    label->setPixmap(pixmap);
+    loadButton->setEnabled(false);
+    resetButton->setEnabled(true);
+    thread->processImage(useImage);
+}
+
+//! [Adding blocks to the display]
+void Window::addBlock(const Block &block)
+{
+    QColor color = block.color();
+    color.setAlpha(64);
+
+    QPainter painter;
+    painter.begin(&pixmap);
+    painter.fillRect(block.rect(), color);
+    painter.end();
+    label->setPixmap(pixmap);
+}
+//! [Adding blocks to the display]
+
+void Window::resetUi()
+{
+    loadButton->setEnabled(true);
+    resetButton->setEnabled(false);
+}

examples/corelib/threads/queuedcustomtype/window.h

@@ -0,0 +1,41 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef WINDOW_H
+#define WINDOW_H
+
+#include <QWidget>
+#include "renderthread.h"
+
+QT_BEGIN_NAMESPACE
+class QLabel;
+class QPushButton;
+QT_END_NAMESPACE
+
+//! [Window class definition]
+class Window : public QWidget
+{
+    Q_OBJECT
+
+public:
+    Window(QWidget *parent = nullptr);
+    void loadImage(const QImage &image);
+
+public slots:
+    void addBlock(const Block &block);
+
+private slots:
+    void loadImage();
+    void resetUi();
+
+private:
+    QLabel *label;
+    QPixmap pixmap;
+    QPushButton *loadButton;
+    QPushButton *resetButton;
+    QString path;
+    RenderThread *thread;
+};
+//! [Window class definition]
+
+#endif

examples/corelib/threads/semaphores/CMakeLists.txt

@@ -0,0 +1,29 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(semaphores LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/threads/semaphores")
+
+find_package(Qt6 REQUIRED COMPONENTS Core)
+
+qt_standard_project_setup()
+
+qt_add_executable(semaphores
+    semaphores.cpp
+)
+
+target_link_libraries(semaphores PRIVATE
+    Qt6::Core
+)
+
+install(TARGETS semaphores
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/threads/semaphores/semaphores.cpp

@@ -0,0 +1,65 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QtCore>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+//! [0]
+const int DataSize = 100000;
+
+const int BufferSize = 8192;
+char buffer[BufferSize];
+
+QSemaphore freeBytes(BufferSize);
+QSemaphore usedBytes;
+//! [0]
+
+//! [1]
+class Producer : public QThread
+//! [1] //! [2]
+{
+public:
+    void run() override
+    {
+        for (int i = 0; i < DataSize; ++i) {
+            freeBytes.acquire();
+            buffer[i % BufferSize] = "ACGT"[QRandomGenerator::global()->bounded(4)];
+            usedBytes.release();
+        }
+    }
+};
+//! [2]
+
+//! [3]
+class Consumer : public QThread
+//! [3] //! [4]
+{
+public:
+    void run() override
+    {
+        for (int i = 0; i < DataSize; ++i) {
+            usedBytes.acquire();
+            fprintf(stderr, "%c", buffer[i % BufferSize]);
+            freeBytes.release();
+        }
+        fprintf(stderr, "\n");
+    }
+};
+//! [4]
+
+//! [5]
+int main(int argc, char *argv[])
+//! [5] //! [6]
+{
+    QCoreApplication app(argc, argv);
+    Producer producer;
+    Consumer consumer;
+    producer.start();
+    consumer.start();
+    producer.wait();
+    consumer.wait();
+    return 0;
+}
+//! [6]

examples/corelib/threads/semaphores/semaphores.pro

@@ -0,0 +1,8 @@
+SOURCES += semaphores.cpp
+QT = core
+
+CONFIG += cmdline
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/threads/semaphores
+INSTALLS += target

examples/corelib/threads/threads.pro

@@ -0,0 +1,9 @@
+TEMPLATE      = subdirs
+CONFIG += no_docs_target
+
+SUBDIRS       = semaphores \
+                waitconditions
+
+qtHaveModule(widgets): SUBDIRS += \
+    mandelbrot \
+    queuedcustomtype

examples/corelib/threads/waitconditions/CMakeLists.txt

@@ -0,0 +1,29 @@
+# Copyright (C) 2022 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(waitconditions LANGUAGES CXX)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/threads/waitconditions")
+
+find_package(Qt6 REQUIRED COMPONENTS Core)
+
+qt_standard_project_setup()
+
+qt_add_executable(waitconditions
+    waitconditions.cpp
+)
+
+target_link_libraries(waitconditions PRIVATE
+    Qt6::Core
+)
+
+install(TARGETS waitconditions
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)

examples/corelib/threads/waitconditions/waitconditions.cpp

@@ -0,0 +1,108 @@
+// Copyright (C) 2016 The Qt Company Ltd.
+// Copyright (C) 2022 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QCoreApplication>
+#include <QMutex>
+#include <QMutexLocker>
+#include <QObject>
+#include <QRandomGenerator>
+#include <QThread>
+#include <QWaitCondition>
+
+#include <stdio.h>
+#include <stdlib.h>
+
+//! [0]
+constexpr int DataSize = 100000;
+constexpr int BufferSize = 8192;
+
+QMutex mutex; // protects the buffer and the counter
+char buffer[BufferSize];
+int numUsedBytes;
+
+QWaitCondition bufferNotEmpty;
+QWaitCondition bufferNotFull;
+//! [0]
+
+//! [1]
+class Producer : public QThread
+//! [1] //! [2]
+{
+public:
+    explicit Producer(QObject *parent = nullptr)
+        : QThread(parent)
+    {
+    }
+
+private:
+    void run() override
+    {
+        for (int i = 0; i < DataSize; ++i) {
+            {
+                const QMutexLocker locker(&mutex);
+                while (numUsedBytes == BufferSize)
+                    bufferNotFull.wait(&mutex);
+            }
+
+            buffer[i % BufferSize] = "ACGT"[QRandomGenerator::global()->bounded(4)];
+
+            {
+                const QMutexLocker locker(&mutex);
+                ++numUsedBytes;
+                bufferNotEmpty.wakeAll();
+            }
+        }
+    }
+};
+//! [2]
+
+//! [3]
+class Consumer : public QThread
+//! [3] //! [4]
+{
+public:
+    explicit Consumer(QObject *parent = nullptr)
+        : QThread(parent)
+    {
+    }
+
+private:
+    void run() override
+    {
+        for (int i = 0; i < DataSize; ++i) {
+            {
+                const QMutexLocker locker(&mutex);
+                while (numUsedBytes == 0)
+                    bufferNotEmpty.wait(&mutex);
+            }
+
+            fprintf(stderr, "%c", buffer[i % BufferSize]);
+
+            {
+                const QMutexLocker locker(&mutex);
+                --numUsedBytes;
+                bufferNotFull.wakeAll();
+            }
+        }
+        fprintf(stderr, "\n");
+    }
+};
+//! [4]
+
+
+//! [5]
+int main(int argc, char *argv[])
+//! [5] //! [6]
+{
+    QCoreApplication app(argc, argv);
+    Producer producer;
+    Consumer consumer;
+    producer.start();
+    consumer.start();
+    producer.wait();
+    consumer.wait();
+    return 0;
+}
+//! [6]
+

examples/corelib/threads/waitconditions/waitconditions.pro

@@ -0,0 +1,9 @@
+QT = core
+CONFIG -= moc
+CONFIG += cmdline
+
+SOURCES += waitconditions.cpp
+
+# install
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/threads/waitconditions
+INSTALLS += target