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< td align = "right" valign = "center" > < img src = "logo32.png" align = "right" width = "64" height = "32" border = "0" > < / td > < / tr > < / table > < h1 align = center > TQThreadStorage Class Reference< / h1 >
< p > The TQThreadStorage class provides per-thread data storage.
< a href = "#details" > More...< / a >
< p > All the functions in this class are < a href = "threads.html#threadsafe" > thread-safe< / a > when TQt is built with thread support.< / p >
< p > < tt > #include < < a href = "tqthreadstorage-h.html" > tqthreadstorage.h< / a > > < / tt >
< p > < a href = "tqthreadstorage-members.html" > List of all member functions.< / a >
< h2 > Public Members< / h2 >
< ul >
< li class = fn > < a href = "#TQThreadStorage" > < b > TQThreadStorage< / b > < / a > ()< / li >
< li class = fn > < a href = "#~TQThreadStorage" > < b > ~TQThreadStorage< / b > < / a > ()< / li >
< li class = fn > bool < a href = "#hasLocalData" > < b > hasLocalData< / b > < / a > () const< / li >
< li class = fn > T & < a href = "#localData" > < b > localData< / b > < / a > ()< / li >
< li class = fn > T < a href = "#localData-2" > < b > localData< / b > < / a > () const< / li >
< li class = fn > void < a href = "#setLocalData" > < b > setLocalData< / b > < / a > ( T data )< / li >
< / ul >
< hr > < a name = "details" > < / a > < h2 > Detailed Description< / h2 >
The TQThreadStorage class provides per-thread data storage.
< p >
< p > TQThreadStorage is a template class that provides per-thread data
storage.
< p > < em > Note that due to compiler limitations, TQThreadStorage can only store pointers.< / em >
< p > The < a href = "#setLocalData" > setLocalData< / a > () function stores a single thread-specific value
for the calling thread. The data can be accessed later using the
< a href = "#localData" > localData< / a > () functions. TQThreadStorage takes ownership of the
data (which must be created on the heap with < em > new< / em > ) and deletes
it when the thread exits (either normally or via termination).
< p > The < a href = "#hasLocalData" > hasLocalData< / a > () function allows the programmer to determine if
data has previously been set using the setLocalData() function.
This is useful for lazy initializiation.
< p > For example, the following code uses TQThreadStorage to store a
single cache for each thread that calls the < em > cacheObject()< / em > and
< em > removeFromCache()< / em > functions. The cache is automatically
deleted when the calling thread exits (either normally or via
termination).
< p > < pre >
TQThreadStorage< TQCache< SomeClass> *> caches;
void cacheObject( const < a href = "tqstring.html" > TQString< / a > & key, SomeClass *object )
{
if ( ! caches.hasLocalData() )
caches.setLocalData( new < a href = "tqcache.html" > TQCache< / a > < SomeClass> );
caches.localData()-> insert( key, object );
}
void removeFromCache( const < a href = "tqstring.html" > TQString< / a > & key )
{
if ( ! caches.hasLocalData() )
return; // nothing to do
caches.localData()-> remove( key );
}
< / pre >
< p > < h3 > Caveats
< / h3 >
< a name = "1" > < / a > < p > < ul >
< p > < li > As noted above, TQThreadStorage 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.
< p > < li > The < a href = "#~TQThreadStorage" > destructor< / a > does < em > not< / em >
delete per-thread data. TQThreadStorage only deletes per-thread
data when the thread exits or when < a href = "#setLocalData" > setLocalData< / a > () is called
multiple times.
< p > < li > TQThreadStorage can only be used with threads started with
< a href = "tqthread.html" > TQThread< / a > . It < em > cannot< / em > be used with threads started with
platform-specific APIs.
< p > < li > As a corollary to the above, platform-specific APIs cannot be
used to exit or terminate a TQThread using TQThreadStorage. Doing so
will cause all per-thread data to be leaked. See < a href = "tqthread.html#exit" > TQThread::exit< / a > ()
and < a href = "tqthread.html#terminate" > TQThread::terminate< / a > ().
< p > < li > TQThreadStorage < em > can< / em > be used to store data for the < em > main()< / em >
thread < em > after< / em > < a href = "ntqapplication.html" > TQApplication< / a > has been constructed. TQThreadStorage
deletes all data set for the < em > main()< / em > thread when TQApplication is
destroyed, regardless of whether or not the < em > main()< / em > thread has
actually finished.
< p > < li > The implementation of TQThreadStorage limits the total number of
TQThreadStorage objects to 256. An unlimited number of threads
can store per-thread data in each TQThreadStorage object.
< p > < / ul >
< p > See also < a href = "environment.html" > Environment Classes< / a > and < a href = "thread.html" > Threading< / a > .
< hr > < h2 > Member Function Documentation< / h2 >
< h3 class = fn > < a name = "TQThreadStorage" > < / a > TQThreadStorage::TQThreadStorage ()
< / h3 >
< p > Constructs a new per-thread data storage object.
< h3 class = fn > < a name = "~TQThreadStorage" > < / a > TQThreadStorage::~TQThreadStorage ()
< / h3 >
< p > Destroys the per-thread data storage object.
< p > Note: The per-thread data stored is < em > not< / em > deleted. Any data left
in TQThreadStorage is leaked. Make sure that all threads using
TQThreadStorage have exited before deleting the TQThreadStorage.
< p > < p > See also < a href = "#hasLocalData" > hasLocalData< / a > ().
< h3 class = fn > bool < a name = "hasLocalData" > < / a > TQThreadStorage::hasLocalData () const
< / h3 >
< p > Returns TRUE if the calling thread has non-zero data available;
otherwise returns FALSE.
< p > < p > See also < a href = "#localData" > localData< / a > ().
< h3 class = fn > T & < a name = "localData" > < / a > TQThreadStorage::localData ()
< / h3 >
< p > Returns a reference to the data that was set by the calling
thread.
< p > Note: TQThreadStorage can only store pointers. This function
returns a < em > reference< / em > 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,
< p > < p > See also < a href = "#hasLocalData" > hasLocalData< / a > ().
< h3 class = fn > T < a name = "localData-2" > < / a > TQThreadStorage::localData () const
< / h3 >
This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
< p > Returns a copy of the data that was set by the calling thread.
< p > Note: TQThreadStorage 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.
< p > < p > See also < a href = "#hasLocalData" > hasLocalData< / a > ().
< h3 class = fn > void < a name = "setLocalData" > < / a > TQThreadStorage::setLocalData ( T data )
< / h3 >
< p > Sets the local data for the calling thread to < em > data< / em > . It can be
accessed later using the < a href = "#localData" > localData< / a > () functions.
< p > If < em > data< / em > is 0, this function deletes the previous data (if
any) and returns immediately.
< p > If < em > data< / em > is non-zero, TQThreadStorage takes ownership of the < em > data< / em > and deletes it automatically either when the thread exits
(either normally or via termination) or when < a href = "#setLocalData" > setLocalData< / a > () is
called again.
< p > Note: TQThreadStorage can only store pointers. The < em > data< / em >
argument must be either a pointer to an object created on the heap
(i.e. using < em > new< / em > ) or 0. You should not delete < em > data< / em >
yourself; TQThreadStorage takes ownership and will delete the < em > data< / em > itself.
< p > < p > See also < a href = "#localData" > localData< / a > () and < a href = "#hasLocalData" > hasLocalData< / a > ().
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