1QThreadStorage(3qt) QThreadStorage(3qt)
2
6 QThreadStorage - Per-thread data storage
7
9 All the functions in this class are thread-safe when Qt is built with
10 thread support.</p>
11 #include <qthreadstorage.h>
13 Public Members
15 QThreadStorage ()
16 ~QThreadStorage ()
17 bool hasLocalData () const
18 T & localData ()
19 T localData () const
20 void setLocalData ( T data )
21
23 The QThreadStorage class provides per-thread data storage.
24 QThreadStorage is a template class that provides per-thread data
26 storage.
27 Note that due to compiler limitations, QThreadStorage can only store
29 pointers.
30 The setLocalData() function stores a single thread-specific value for
32 the calling thread. The data can be accessed later using the
33 localData() functions. QThreadStorage takes ownership of the data
34 (which must be created on the heap with new) and deletes it when the
35 thread exits (either normally or via termination).
36 The hasLocalData() function allows the programmer to determine if data
38 has previously been set using the setLocalData() function. This is
39 useful for lazy initializiation.
40 For example, the following code uses QThreadStorage to store a single
42 cache for each thread that calls the cacheObject() and
43 removeFromCache() functions. The cache is automatically deleted when
44 the calling thread exits (either normally or via termination).
45 QThreadStorage<QCache<SomeClass> *> caches;
47 void cacheObject( const QString &key, SomeClass *object )
48 {
49 if ( ! caches.hasLocalData() )
50 caches.setLocalData( new QCache<SomeClass> );
51 caches.localData()->insert( key, object );
52 }
53 void removeFromCache( const QString &key )
54 {
55 if ( ! caches.hasLocalData() )
56 return; // nothing to do
57 caches.localData()->remove( key );
58 }
59
61 As noted above, QThreadStorage can only store pointers due to compiler
62 limitations. Support for value-based objects will be added when the
63 majority of compilers are able to support partial template
64 specialization.
65 The destructor does not delete per-thread data. QThreadStorage only
67 deletes per-thread data when the thread exits or when setLocalData() is
68 called multiple times.
69 QThreadStorage can only be used with threads started with QThread. It
71 cannot be used with threads started with platform-specific APIs.
72 As a corollary to the above, platform-specific APIs cannot be used to
74 exit or terminate a QThread using QThreadStorage. Doing so will cause
75 all per-thread data to be leaked. See QThread::exit() and
76 QThread::terminate().
77 QThreadStorage can be used to store data for the main() thread after
79 QApplication has been constructed. QThreadStorage deletes all data set
80 for the main() thread when QApplication is destroyed, regardless of
81 whether or not the main() thread has actually finished.
82 The implementation of QThreadStorage limits the total number of
84 QThreadStorage objects to 256. An unlimited number of threads can store
85 per-thread data in each QThreadStorage object.
86 See also Environment Classes and Threading.
88
91 Constructs a new per-thread data storage object.
92
94 Destroys the per-thread data storage object.
95 Note: The per-thread data stored is not deleted. Any data left in
97 QThreadStorage is leaked. Make sure that all threads using
98 QThreadStorage have exited before deleting the QThreadStorage.
99 See also hasLocalData().
101
103 Returns TRUE if the calling thread has non-zero data available;
104 otherwise returns FALSE.
105 See also localData().
107
109 Returns a reference to the data that was set by the calling thread.
110 Note: QThreadStorage can only store pointers. This function returns a
112 reference to the pointer that was set by the calling thread. The value
113 of this reference is 0 if no data was set by the calling thread,
114 See also hasLocalData().
116
118 This is an overloaded member function, provided for convenience. It
119 behaves essentially like the above function.
120 Returns a copy of the data that was set by the calling thread.
122 Note: QThreadStorage can only store pointers. This function returns a
124 pointer to the data that was set by the calling thread. If no data was
125 set by the calling thread, this function returns 0.
126 See also hasLocalData().
128
130 Sets the local data for the calling thread to data. It can be accessed
131 later using the localData() functions.
132 If data is 0, this function deletes the previous data (if any) and
134 returns immediately.
135 If data is non-zero, QThreadStorage takes ownership of the data and
137 deletes it automatically either when the thread exits (either normally
138 or via termination) or when setLocalData() is called again.
139 Note: QThreadStorage can only store pointers. The data argument must be
141 either a pointer to an object created on the heap (i.e. using new) or
142 0. You should not delete data yourself; QThreadStorage takes ownership
143 and will delete the data itself.
144 See also localData() and hasLocalData().
146
149 http://doc.trolltech.com/qthreadstorage.html
150 http://www.trolltech.com/faq/tech.html
151
153 Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
154 license file included in the distribution for a complete license
155 statement.
156
158 Generated automatically from the source code.
159
161 If you find a bug in Qt, please report it as described in
162 http://doc.trolltech.com/bughowto.html. Good bug reports help us to
163 help you. Thank you.
164 The definitive Qt documentation is provided in HTML format; it is
166 located at $QTDIR/doc/html and can be read using Qt Assistant or with a
167 web browser. This man page is provided as a convenience for those users
168 who prefer man pages, although this format is not officially supported
169 by Trolltech.
170 If you find errors in this manual page, please report them to qt-
172 bugs@trolltech.com. Please include the name of the manual page
173 (qthreadstorage.3qt) and the Qt version (3.3.8).
174Trolltech AS 2 February 2007 QThreadStorage(3qt)