From cf8f369f8575dcb9ca4d5116f3afc7cff4a080af Mon Sep 17 00:00:00 2001 From: Topi Reinio Date: Wed, 15 Oct 2014 13:50:27 +0200 Subject: Move Qt Core examples under a common subdirectory Qt Core examples were scattered into several subdirectories under qtbase/examples. This caused an issue with the example manifest file generated by QDoc; it expects to find all examples under a common directory in order to produde correct paths to the example .pro files. Qt Creator will not find the examples without a valid manifest file. This change moves the examples and edits the documentation files accordingly. Task-number: QTBUG-41963 Change-Id: I51d86782e0ba21c5c9bae5f15401ec774abe5cf8 Reviewed-by: Friedemann Kleint Reviewed-by: Oswald Buddenhagen Reviewed-by: Leena Miettinen --- examples/threads/doc/src/waitconditions.qdoc | 154 --------------------------- 1 file changed, 154 deletions(-) delete mode 100644 examples/threads/doc/src/waitconditions.qdoc (limited to 'examples/threads/doc/src/waitconditions.qdoc') diff --git a/examples/threads/doc/src/waitconditions.qdoc b/examples/threads/doc/src/waitconditions.qdoc deleted file mode 100644 index 25c9ce88fb..0000000000 --- a/examples/threads/doc/src/waitconditions.qdoc +++ /dev/null @@ -1,154 +0,0 @@ -/**************************************************************************** -** -** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies). -** Contact: http://www.qt-project.org/legal -** -** 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 Digia. For licensing terms and -** conditions see http://qt.digia.com/licensing. For further information -** use the contact form at http://qt.digia.com/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: http://www.gnu.org/copyleft/fdl.html. -** $QT_END_LICENSE$ -** -****************************************************************************/ - -/*! - \example 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 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 waitconditions/waitconditions.cpp 1 - \snippet 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 waitconditions/waitconditions.cpp 3 - \snippet 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 waitconditions/waitconditions.cpp 5 - \snippet 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 \c BufferSize - 1 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 consumer 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. -*/ -- cgit v1.2.3