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1 /**************************************************************************** |
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2 ** |
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3 ** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies). |
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4 ** All rights reserved. |
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5 ** Contact: Nokia Corporation (qt-info@nokia.com) |
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7 ** This file is part of the documentation of the Qt Toolkit. |
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16 ** GNU Lesser General Public License Usage |
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18 ** General Public License version 2.1 as published by the Free Software |
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24 ** In addition, as a special exception, Nokia gives you certain additional |
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35 ** |
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36 ** |
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37 ** |
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38 ** $QT_END_LICENSE$ |
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39 ** |
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40 ****************************************************************************/ |
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41 |
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42 /*! |
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43 \page qt4-threads.html |
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44 \title Thread Support in Qt 4 |
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45 |
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46 \contentspage {What's New in Qt 4}{Home} |
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47 \previouspage The Qt 4 Style API |
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48 |
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49 Qt 4 makes it easier than ever to write multithreaded |
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50 applications. More classes have been made usable from non-GUI |
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51 threads, and the signals and slots mechanism can now be used to |
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52 communicate between threads. |
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53 |
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54 \section1 General Overview |
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55 |
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56 QThread now inherits QObject. It emits signals to indicate that |
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57 the thread started or finished executing, and provides a few |
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58 slots as well. |
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59 |
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60 Each thread can now have its own event loop. The initial thread |
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61 starts its event loops using QCoreApplication::exec(); other |
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62 threads can start an event loop using QThread::exec(). Like |
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63 QCoreApplication, QThread also provides an |
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64 \l{QThread::exit()}{exit(int)} function and a |
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65 \l{QThread::quit()}{quit()} slot. |
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66 |
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67 An event loop in a thread makes it possible for the thread to use |
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68 certain non-GUI Qt classes that require the presence of an event |
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69 loop (such as QTimer, QTcpSocket, and QProcess). It also makes it |
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70 possible to connect signals from any threads to slots of a |
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71 specific thread. When a signal is emitted, the slot isn't called |
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72 immediately; instead, it is invoked when control returns to the |
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73 event loop of the thread to which the object belongs. The slot is |
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74 executed in the thread where the receiver object lives. See |
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75 QObject::connect() for details. |
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76 |
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77 Qt 4 also introduces a new synchronization class: QReadWriteLock. |
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78 It is similar to QMutex, except that it distinguishes between |
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79 "read" and "write" access to shared data and allows multiple |
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80 readers to access the data simultaneously. Using QReadWriteLock |
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81 instead of QMutex when it is possible can make multithreaded |
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82 programs more concurrent. |
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83 |
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84 Since Qt 4, \l{implicitly shared} classes can safely be copied |
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85 across threads, like any other value classes. They are fully |
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86 reentrant. This is implemented using atomic reference counting |
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87 operations, which are implemented in assembly language for the |
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88 different platforms supported by Qt. Atomic reference counting is |
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89 very fast, much faster than using a mutex. |
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90 |
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91 See \l{Thread Support in Qt} for more information. |
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92 |
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93 \section1 Comparison with Qt 3 |
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94 |
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95 Earlier versions of Qt offered an option to build the library |
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96 without thread support. In Qt 4, threads are always enabled. |
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97 |
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98 Qt 3 had a class called \c QDeepCopy that you could use to take a |
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99 deep copy of an implicitly shared object. In Qt 4, the atomic |
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100 reference counting makes this class superfluous. |
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101 */ |