qt-everywhere-src-5.14.1/qtbase/examples/network/doc/src/threadedfortuneserver.qdoc

/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: https://www.gnu.org/licenses/fdl-1.3.html.
** $QT_END_LICENSE$
**
****************************************************************************/

/*!
    \example threadedfortuneserver
    \title Threaded Fortune Server Example
    \ingroup examples-network

    \brief The Threaded Fortune Server example shows how to create a server for a
    simple network service that uses threads to handle requests from different
    clients. It is intended to be run alongside the Fortune Client example.

    \image threadedfortuneserver-example.png

    The implementation of this example is similar to that of the
    \l{fortuneserver}{Fortune Server} example, but here we will
    implement a subclass of QTcpServer that starts each connection in a
    different thread.

    For this we need two classes: FortuneServer, a QTcpServer subclass, and
    FortuneThread, which inherits QThread.

    \snippet threadedfortuneserver/fortuneserver.h 0

    FortuneServer inherits QTcpServer and reimplements
    QTcpServer::incomingConnection(). We also use it for storing the list of
    random fortunes.

    \snippet threadedfortuneserver/fortuneserver.cpp 0

    We use FortuneServer's constructor to simply generate the list of
    fortunes.

    \snippet threadedfortuneserver/fortuneserver.cpp 1

    Our implementation of QTcpServer::incomingConnection() creates a
    FortuneThread object, passing the incoming socket descriptor and a random
    fortune to FortuneThread's constructor. By connecting FortuneThread's
    finished() signal to QObject::deleteLater(), we ensure that the thread
    gets deleted once it has finished. We can then call QThread::start(),
    which starts the thread.

    \snippet threadedfortuneserver/fortunethread.h 0

    Moving on to the FortuneThread class, this is a QThread subclass whose job
    is to write the fortune to the connected socket. The class reimplements
    QThread::run(), and it has a signal for reporting errors.

    \snippet threadedfortuneserver/fortunethread.cpp 0

    FortuneThread's constructor simply stores the socket descriptor and
    fortune text, so that they are available for run() later on.

    \snippet threadedfortuneserver/fortunethread.cpp 1

    The first thing our run() function does is to create a QTcpSocket object
    on the stack. What's worth noticing is that we are creating this object
    inside the thread, which automatically associates the socket to the
    thread's event loop. This ensures that Qt will not try to deliver events
    to our socket from the main thread while we are accessing it from
    FortuneThread::run().

    \snippet threadedfortuneserver/fortunethread.cpp 2

    The socket is initialized by calling QTcpSocket::setSocketDescriptor(),
    passing our socket descriptor as an argument. We expect this to succeed,
    but just to be sure, (although unlikely, the system may run out of
    resources,) we catch the return value and report any error.

    \snippet threadedfortuneserver/fortunethread.cpp 3

    As with the \l{fortuneserver}{Fortune Server} example, we encode
    the fortune into a QByteArray using QDataStream.

    \snippet threadedfortuneserver/fortunethread.cpp 4

    But unlike the previous example, we finish off by calling
    QTcpSocket::waitForDisconnected(), which blocks the calling thread until
    the socket has disconnected. Because we are running in a separate thread,
    the GUI will remain responsive.

    \sa {Fortune Server Example}, {Fortune Client Example}, {Blocking Fortune
    Client Example}
*/