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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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