diff options
Diffstat (limited to 'src/corelib/doc/src/threads-basics.qdoc')
| -rw-r--r-- | src/corelib/doc/src/threads-basics.qdoc | 105 |
1 files changed, 6 insertions, 99 deletions
diff --git a/src/corelib/doc/src/threads-basics.qdoc b/src/corelib/doc/src/threads-basics.qdoc index dd5267f0ba..5a5c003210 100644 --- a/src/corelib/doc/src/threads-basics.qdoc +++ b/src/corelib/doc/src/threads-basics.qdoc @@ -172,109 +172,16 @@ \section2 Which Qt Thread Technology Should You Use? - Sometimes you want to do more than just running a method in the context of - another thread. You may want to have an object which lives in another - thread that provides a service to the GUI thread. Maybe you want another - thread to stay alive forever to poll hardware ports and send a signal to - the GUI thread when something noteworthy has happened. Qt provides - different solutions for developing threaded applications. The right - solution depends on the purpose of the new thread as well as on the - thread's lifetime. - - \table - \header - \li Lifetime of thread - \li Development task - \li Solution - \row - \li One call - \li Run one method within another thread and quit the thread when the - method is finished. - \li Qt provides different solutions: - \list - \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() - \li Derive a class from QThread, reimplement the QThread::run() - method and use QThread::start() to run it. - \endlist - - \row - \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. - \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 - \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. - \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 - \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. - \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 - \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. - \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 + See the \l{Multithreading Technologies in Qt} page for an introduction to the + different approaches to multithreading to Qt, and for guidelines on how to + choose among them. \section1 Qt Thread Basics - QThread is a very convenient cross platform abstraction of native platform - threads. Starting a thread is very simple. Let us look at a short piece of - code that generates another thread which says hello in that thread and then - exits. - - \snippet ../widgets/tutorials/threads/hellothread/hellothread.h 1 - - We derive a class from QThread and reimplement the \l{QThread::}{run()} - method. - - \snippet ../widgets/tutorials/threads/hellothread/hellothread.cpp 1 - - The run method contains the code that will be run in a separate thread. In - this example, a message containing the thread ID will be printed. - QThread::start() will call the method in another thread. - - \snippet ../widgets/tutorials/threads/hellothread/main.cpp 1 - - To start the thread, our thread object needs to be instantiated. The - \l{QThread::}{start()} method creates a new thread and calls the - reimplemented \l{QThread::}{run()} method in this new thread. Right after - \l{QThread::}{start()} is called, two program counters walk through the - program code. The main function starts with only the GUI thread running and - it should terminate with only the GUI thread running. Exiting the program - when another thread is still busy is a programming error, and therefore, - wait is called which blocks the calling thread until the - \l{QThread::}{run()} method has completed. - - This is the result of running the code: - - \code - //bad code - hello from GUI thread 3079423696 - hello from worker thread 3076111216 - \endcode - + The following sections describe how QObjects interact with threads, how + programs can safely access data from multiple threads, and how asynchronous + execution produces results without blocking a thread. \section2 QObject and Threads |