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Diffstat (limited to 'doc/src/corelib/threads-basics.qdoc')
| -rw-r--r-- | doc/src/corelib/threads-basics.qdoc | 88 |
1 files changed, 44 insertions, 44 deletions
diff --git a/doc/src/corelib/threads-basics.qdoc b/doc/src/corelib/threads-basics.qdoc index 44a3961177..e54f8a7ccb 100644 --- a/doc/src/corelib/threads-basics.qdoc +++ b/doc/src/corelib/threads-basics.qdoc @@ -123,8 +123,8 @@ There are basically two use cases for threads: \list - \o Make processing faster by making use of multicore processors. - \o Keep the GUI thread or other time critical threads responsive by + \li Make processing faster by making use of multicore processors. + \li Keep the GUI thread or other time critical threads responsive by offloading long lasting processing or blocking calls to other threads. \endlist @@ -138,23 +138,23 @@ \table \header - \o Alternative - \o Comment + \li Alternative + \li Comment \row - \o QEventLoop::processEvents() - \o Calling QEventLoop::processEvents() repeatedly during a + \li QEventLoop::processEvents() + \li Calling QEventLoop::processEvents() repeatedly during a time-consuming calculation prevents GUI blocking. However, this solution doesn't scale well because the call to processEvents() may occur too often, or not often enough, depending on hardware. \row - \o QTimer - \o Background processing can sometimes be done conveniently using a + \li QTimer + \li Background processing can sometimes be done conveniently using a timer to schedule execution of a slot at some point in the future. A timer with an interval of 0 will time out as soon as there are no more events to process. \row - \o QSocketNotifier QNetworkAccessManager QIODevice::readyRead() - \o This is an alternative to having one or multiple threads, each with + \li QSocketNotifier QNetworkAccessManager QIODevice::readyRead() + \li This is an alternative to having one or multiple threads, each with a blocking read on a slow network connection. As long as the calculation in response to a chunk of network data can be executed quickly, this reactive design is better than synchronous waiting in @@ -183,55 +183,55 @@ \table \header - \o Lifetime of thread - \o Development task - \o Solution + \li Lifetime of thread + \li Development task + \li Solution \row - \o One call - \o Run one method within another thread and quit the thread when the + \li One call + \li Run one method within another thread and quit the thread when the method is finished. - \o Qt provides different solutions: + \li Qt provides different solutions: \list - \o Write a function and run it with QtConcurrent::run() - \o Derive a class from QRunnable and run it in the global thread + \li Write a function and run it with QtConcurrent::run() + \li Derive a class from QRunnable and run it in the global thread pool with QThreadPool::globalInstance()->start() - \o Derive a class from QThread, reimplement the QThread::run() + \li Derive a class from QThread, reimplement the QThread::run() method and use QThread::start() to run it. \endlist \row - \o One call - \o Operations are to be performed on all items of a container. + \li One call + \li Operations are to be performed on all items of a container. Processing should be performed using all available cores. A common example is to produce thumbnails from a list of images. - \o QtConcurrent provides the \l{QtConcurrent::}{map()} function for + \li QtConcurrent provides the \l{QtConcurrent::}{map()} function for applying operations on every container element, \l{QtConcurrent::}{filter()} for selecting container elements, and the option of specifying a reduce function for combining the remaining elements. \row - \o One call - \o A long running operation has to be put in another thread. During the + \li One call + \li A long running operation has to be put in another thread. During the course of processing, status information should be sent to the GUI thread. - \o Use QThread, reimplement run and emit signals as needed. Connect the + \li Use QThread, reimplement run and emit signals as needed. Connect the signals to the GUI thread's slots using queued signal/slot connections. \row - \o Permanent - \o Have an object living in another thread and let it perform different + \li Permanent + \li Have an object living in another thread and let it perform different tasks upon request. This means communication to and from the worker thread is required. - \o Derive a class from QObject and implement the necessary slots and + \li Derive a class from QObject and implement the necessary slots and signals, move the object to a thread with a running event loop and communicate with the object over queued signal/slot connections. \row - \o Permanent - \o Have an object living in another thread, let the object perform + \li Permanent + \li Have an object living in another thread, let the object perform repeated tasks such as polling a port and enable communication with the GUI thread. - \o Same as above but also use a timer in the worker thread to implement + \li Same as above but also use a timer in the worker thread to implement polling. However, the best solution for polling is to avoid it completely. Sometimes using QSocketNotifier is an alternative. \endtable @@ -304,18 +304,18 @@ The anatomy of QThread is quite interesting: \list - \o QThread does not live in the new thread where \l{QThread::}{run()} is + \li QThread does not live in the new thread where \l{QThread::}{run()} is executed. It lives in the old thread. - \o Most QThread methods are the thread's control interface and are meant to + \li Most QThread methods are the thread's control interface and are meant to be called from the old thread. Do not move this interface to the newly created thread using \l{QObject::}{moveToThread()}; i.e., calling \l{QObject::moveToThread()}{moveToThread(this)} is regarded as bad practice. - \o \l{QThread::}{exec()} and the static methods + \li \l{QThread::}{exec()} and the static methods \l{QThread::}{usleep()}, \l{QThread::}{msleep()}, \l{QThread::}{sleep()} are meant to be called from the newly created thread. - \o Additional members defined in the QThread subclass are + \li Additional members defined in the QThread subclass are accessible by both threads. The developer is responsible for coordinating access. A typical strategy is to set the members before \l{QThread::}{start()} is called. Once the worker thread is running, @@ -432,11 +432,11 @@ main thread. \list - \o Using QThread as shown \l{Qt thread basics}{above} - \o \l{Example 1: Using the Thread Pool}{Using the global QThreadPool} - \o \l{Example 2: Using QtConcurrent}{Using QtConcurrent} - \o \l{Example 3: Clock}{Communication with the GUI thread} - \o \l{Example 4: A Permanent Thread}{A permanent QObject in another thread + \li Using QThread as shown \l{Qt thread basics}{above} + \li \l{Example 1: Using the Thread Pool}{Using the global QThreadPool} + \li \l{Example 2: Using QtConcurrent}{Using QtConcurrent} + \li \l{Example 3: Clock}{Communication with the GUI thread} + \li \l{Example 4: A Permanent Thread}{A permanent QObject in another thread provides service to the main thread} \endlist @@ -558,13 +558,13 @@ can help you go into the subject in more depth: \list - \o Good video tutorials about threads with Qt can be found in the material + \li Good video tutorials about threads with Qt can be found in the material from the \l{Training Day at Qt Developer Days 2009}. - \o The \l{Thread Support in Qt} document is a good starting point into + \li The \l{Thread Support in Qt} document is a good starting point into the reference documentation. - \o Qt comes with several additional examples for + \li Qt comes with several additional examples for \l{Threading and Concurrent Programming Examples}{QThread and QtConcurrent}. - \o Several good books describe how to work with Qt threads. The most + \li Several good books describe how to work with Qt threads. The most extensive coverage can be found in \e{Advanced Qt Programming} by Mark Summerfield, Prentice Hall - roughly 70 of 500 pages cover QThread and QtConcurrent. |