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QThreadStorage(3qt)							      QThreadStorage(3qt)

NAME
       QThreadStorage - Per-thread data storage

SYNOPSIS
       All the functions in this class are thread-safe when Qt is built with thread support.</p>

       #include <qthreadstorage.h>

   Public Members
       QThreadStorage ()
       ~QThreadStorage ()
       bool hasLocalData () const
       T & localData ()
       T localData () const
       void setLocalData ( T data )

DESCRIPTION
       The QThreadStorage class provides per-thread data storage.

       QThreadStorage is a template class that provides per-thread data storage.

       Note that due to compiler limitations, QThreadStorage can only store pointers.

       The setLocalData() function stores a single thread-specific value for the calling thread.
       The data can be accessed later using the localData() functions. QThreadStorage takes
       ownership of the data (which must be created on the heap with new) and deletes it when the
       thread exits (either normally or via termination).

       The hasLocalData() function allows the programmer to determine if data has previously been
       set using the setLocalData() function. This is useful for lazy initializiation.

       For example, the following code uses QThreadStorage to store a single cache for each
       thread that calls the cacheObject() and removeFromCache() functions. The cache is
       automatically deleted when the calling thread exits (either normally or via termination).

	   QThreadStorage<QCache<SomeClass> *> caches;
	   void cacheObject( const QString &key, SomeClass *object )
	   {
	       if ( ! caches.hasLocalData() )
		   caches.setLocalData( new QCache<SomeClass> );
	       caches.localData()->insert( key, object );
	   }
	   void removeFromCache( const QString &key )
	   {
	       if ( ! caches.hasLocalData() )
		   return; // nothing to do
	       caches.localData()->remove( key );
	   }

Caveats
       As noted above, QThreadStorage can only store pointers due to compiler limitations.
       Support for value-based objects will be added when the majority of compilers are able to
       support partial template specialization.

       The destructor does not delete per-thread data. QThreadStorage only deletes per-thread
       data when the thread exits or when setLocalData() is called multiple times.

       QThreadStorage can only be used with threads started with QThread. It cannot be used with
       threads started with platform-specific APIs.

       As a corollary to the above, platform-specific APIs cannot be used to exit or terminate a
       QThread using QThreadStorage. Doing so will cause all per-thread data to be leaked. See
       QThread::exit() and QThread::terminate().

       QThreadStorage can be used to store data for the main() thread after QApplication has been
       constructed. QThreadStorage deletes all data set for the main() thread when QApplication
       is destroyed, regardless of whether or not the main() thread has actually finished.

       The implementation of QThreadStorage limits the total number of QThreadStorage objects to
       256. An unlimited number of threads can store per-thread data in each QThreadStorage
       object.

       See also Environment Classes and Threading.

MEMBER FUNCTION DOCUMENTATION
QThreadStorage::QThreadStorage ()
       Constructs a new per-thread data storage object.

QThreadStorage::~QThreadStorage ()
       Destroys the per-thread data storage object.

       Note: The per-thread data stored is not deleted. Any data left in QThreadStorage is
       leaked. Make sure that all threads using QThreadStorage have exited before deleting the
       QThreadStorage.

       See also hasLocalData().

bool QThreadStorage::hasLocalData () const
       Returns TRUE if the calling thread has non-zero data available; otherwise returns FALSE.

       See also localData().

T &; QThreadStorage::localData ()
       Returns a reference to the data that was set by the calling thread.

       Note: QThreadStorage can only store pointers. This function returns a reference to the
       pointer that was set by the calling thread. The value of this reference is 0 if no data
       was set by the calling thread,

       See also hasLocalData().

T QThreadStorage::localData () const
       This is an overloaded member function, provided for convenience. It behaves essentially
       like the above function.

       Returns a copy of the data that was set by the calling thread.

       Note: QThreadStorage can only store pointers. This function returns a pointer to the data
       that was set by the calling thread. If no data was set by the calling thread, this
       function returns 0.

       See also hasLocalData().

void QThreadStorage::setLocalData ( T data )
       Sets the local data for the calling thread to data. It can be accessed later using the
       localData() functions.

       If data is 0, this function deletes the previous data (if any) and returns immediately.

       If data is non-zero, QThreadStorage takes ownership of the data and deletes it
       automatically either when the thread exits (either normally or via termination) or when
       setLocalData() is called again.

       Note: QThreadStorage can only store pointers. The data argument must be either a pointer
       to an object created on the heap (i.e. using new) or 0. You should not delete data
       yourself; QThreadStorage takes ownership and will delete the data itself.

       See also localData() and hasLocalData().

SEE ALSO
       http://doc.trolltech.com/qthreadstorage.html http://www.trolltech.com/faq/tech.html

COPYRIGHT
       Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com.  See the license file
       included in the distribution for a complete license statement.

AUTHOR
       Generated automatically from the source code.

BUGS
       If you find a bug in Qt, please report it as described in
       http://doc.trolltech.com/bughowto.html.	Good bug reports help us to help you. Thank you.

       The definitive Qt documentation is provided in HTML format; it is located at
       $QTDIR/doc/html and can be read using Qt Assistant or with a web browser. This man page is
       provided as a convenience for those users who prefer man pages, although this format is
       not officially supported by Trolltech.

       If you find errors in this manual page, please report them to qt-bugs@trolltech.com.
       Please include the name of the manual page (qthreadstorage.3qt) and the Qt version
       (3.3.8).

Trolltech AS				 2 February 2007		      QThreadStorage(3qt)
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