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diff --git a/doc/src/examples/blockingfortuneclient.qdoc b/doc/src/examples/blockingfortuneclient.qdoc deleted file mode 100644 index 6c3be78859..0000000000 --- a/doc/src/examples/blockingfortuneclient.qdoc +++ /dev/null @@ -1,216 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2012 Nokia Corporation and/or its subsidiary(-ies). -** Contact: http://www.qt-project.org/ -** -** This file is part of the documentation of the Qt Toolkit. -** -** $QT_BEGIN_LICENSE:FDL$ -** GNU Free Documentation License -** 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. -** -** Other Usage -** Alternatively, this file may be used in accordance with the terms -** and conditions contained in a signed written agreement between you -** and Nokia. -** -** -** -** -** -** $QT_END_LICENSE$ -** -****************************************************************************/ - -/*! - \example network/blockingfortuneclient - \title Blocking Fortune Client Example - - The Blocking Fortune Client example shows how to create a client for a - network service using QTcpSocket's synchronous API in a non-GUI thread. - - \image blockingfortuneclient-example.png - - QTcpSocket supports two general approaches to network programming: - - \list - - \li \e{The asynchronous (non-blocking) approach.} Operations are scheduled - and performed when control returns to Qt's event loop. When the operation - is finished, QTcpSocket emits a signal. For example, - QTcpSocket::connectToHost() returns immediately, and when the connection - has been established, QTcpSocket emits - \l{QTcpSocket::connected()}{connected()}. - - \li \e{The synchronous (blocking) approach.} In non-GUI and multithreaded - applications, you can call the \c waitFor...() functions (e.g., - QTcpSocket::waitForConnected()) to suspend the calling thread until the - operation has completed, instead of connecting to signals. - - \endlist - - The implementation is very similar to the - \l{network/fortuneclient}{Fortune Client} example, but instead of having - QTcpSocket as a member of the main class, doing asynchronous networking in - the main thread, we will do all network operations in a separate thread - and use QTcpSocket's blocking API. - - The purpose of this example is to demonstrate a pattern that you can use - to simplify your networking code, without losing responsiveness in your - user interface. Use of Qt's blocking network API often leads to - simpler code, but because of its blocking behavior, it should only be used - in non-GUI threads to prevent the user interface from freezing. But - contrary to what many think, using threads with QThread does not - necessarily add unmanagable complexity to your application. - - We will start with the FortuneThread class, which handles the network - code. - - \snippet examples/network/blockingfortuneclient/fortunethread.h 0 - - FortuneThread is a QThread subclass that provides an API for scheduling - requests for fortunes, and it has signals for delivering fortunes and - reporting errors. You can call requestNewFortune() to request a new - fortune, and the result is delivered by the newFortune() signal. If any - error occurs, the error() signal is emitted. - - It's important to notice that requestNewFortune() is called from the main, - GUI thread, but the host name and port values it stores will be accessed - from FortuneThread's thread. Because we will be reading and writing - FortuneThread's data members from different threads concurrently, we use - QMutex to synchronize access. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 2 - - The requestNewFortune() function stores the host name and port of the - fortune server as member data, and we lock the mutex with QMutexLocker to - protect this data. We then start the thread, unless it is already - running. We will come back to the QWaitCondition::wakeOne() call later. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 4 - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 5 - - In the run() function, we start by acquiring the mutex lock, fetching the - host name and port from the member data, and then releasing the lock - again. The case that we are protecting ourselves against is that \c - requestNewFortune() could be called at the same time as we are fetching - this data. QString is \l reentrant but \e not \l{thread-safe}, and we must - also avoid the unlikely risk of reading the host name from one request, - and port of another. And as you might have guessed, FortuneThread can only - handle one request at a time. - - The run() function now enters a loop: - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 6 - - The loop will continue requesting fortunes for as long as \e quit is - false. We start our first request by creating a QTcpSocket on the stack, - and then we call \l{QTcpSocket::connectToHost()}{connectToHost()}. This - starts an asynchronous operation which, after control returns to Qt's - event loop, will cause QTcpSocket to emit - \l{QTcpSocket::connected()}{connected()} or - \l{QTcpSocket::error()}{error()}. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 8 - - But since we are running in a non-GUI thread, we do not have to worry - about blocking the user interface. So instead of entering an event loop, - we simply call QTcpSocket::waitForConnected(). This function will wait, - blocking the calling thread, until QTcpSocket emits connected() or an - error occurs. If connected() is emitted, the function returns true; if the - connection failed or timed out (which in this example happens after 5 - seconds), false is returned. QTcpSocket::waitForConnected(), like the - other \c waitFor...() functions, is part of QTcpSocket's \e{blocking - API}. - - After this statement, we have a connected socket to work with. Now it's - time to see what the fortune server has sent us. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 9 - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 10 - - This step is to read the size of the packet. Although we are only reading - two bytes here, and the \c while loop may seem to overdo it, we present this - code to demonstrate a good pattern for waiting for data using - QTcpSocket::waitForReadyRead(). It goes like this: For as long as we still - need more data, we call waitForReadyRead(). If it returns false, - we abort the operation. After this statement, we know that we have received - enough data. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 11 - - Now we can create a QDataStream object, passing the socket to - QDataStream's constructor, and as in the other client examples we set - the stream protocol version to QDataStream::Qt_4_0, and read the size - of the packet. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 12 - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 13 - - Again, we'll use a loop that waits for more data by calling - QTcpSocket::waitForReadyRead(). In this loop, we're waiting until - QTcpSocket::bytesAvailable() returns the full packet size. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 14 - - Now that we have all the data that we need, we can use QDataStream to - read the fortune string from the packet. The resulting fortune is - delivered by emitting newFortune(). - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 15 - - The final part of our loop is that we acquire the mutex so that we can - safely read from our member data. We then let the thread go to sleep by - calling QWaitCondition::wait(). At this point, we can go back to - requestNewFortune() and look closed at the call to wakeOne(): - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 1 - \dots - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 3 - - What happened here was that because the thread falls asleep waiting for a - new request, we needed to wake it up again when a new request - arrives. QWaitCondition is often used in threads to signal a wakeup call - like this. - - \snippet examples/network/blockingfortuneclient/fortunethread.cpp 0 - - Finishing off the FortuneThread walkthrough, this is the destructor that - sets \e quit to true, wakes up the thread and waits for the thread to exit - before returning. This lets the \c while loop in run() will finish its current - iteration. When run() returns, the thread will terminate and be destroyed. - - Now for the BlockingClient class: - - \snippet examples/network/blockingfortuneclient/blockingclient.h 0 - - BlockingClient is very similar to the Client class in the - \l{network/fortuneclient}{Fortune Client} example, but in this class - we store a FortuneThread member instead of a pointer to a QTcpSocket. - When the user clicks the "Get Fortune" button, the same slot is called, - but its implementation is slightly different: - - \snippet examples/network/blockingfortuneclient/blockingclient.cpp 0 - \snippet examples/network/blockingfortuneclient/blockingclient.cpp 1 - - We connect our FortuneThread's two signals newFortune() and error() (which - are somewhat similar to QTcpSocket::readyRead() and QTcpSocket::error() in - the previous example) to requestNewFortune() and displayError(). - - \snippet examples/network/blockingfortuneclient/blockingclient.cpp 2 - - The requestNewFortune() slot calls FortuneThread::requestNewFortune(), - which \e shedules the request. When the thread has received a new fortune - and emits newFortune(), our showFortune() slot is called: - - \snippet examples/network/blockingfortuneclient/blockingclient.cpp 3 - \codeline - \snippet examples/network/blockingfortuneclient/blockingclient.cpp 4 - - Here, we simply display the fortune we received as the argument. - - \sa {Fortune Client Example}, {Fortune Server Example} -*/ |