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190 lines
8.6 KiB
190 lines
8.6 KiB
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<!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qthreadstorage_unix.cpp:163 -->
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<title>TQThreadStorage Class</title>
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<font color="#004faf">Home</font></a>
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<font color="#004faf">All Classes</font></a>
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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>
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<p>The TQThreadStorage class provides per-thread data storage.
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<a href="#details">More...</a>
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<p>All the functions in this class are <a href="threads.html#threadsafe">thread-safe</a> when TQt is built with thread support.</p>
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<p><tt>#include <<a href="qthreadstorage-h.html">ntqthreadstorage.h</a>></tt>
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<p><a href="qthreadstorage-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#TQThreadStorage"><b>TQThreadStorage</b></a> ()</li>
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<li class=fn><a href="#~TQThreadStorage"><b>~TQThreadStorage</b></a> ()</li>
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<li class=fn>bool <a href="#hasLocalData"><b>hasLocalData</b></a> () const</li>
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<li class=fn>T & <a href="#localData"><b>localData</b></a> ()</li>
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<li class=fn>T <a href="#localData-2"><b>localData</b></a> () const</li>
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<li class=fn>void <a href="#setLocalData"><b>setLocalData</b></a> ( T data )</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The TQThreadStorage class provides per-thread data storage.
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<p>
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<p> TQThreadStorage is a template class that provides per-thread data
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storage.
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<p> <em>Note that due to compiler limitations, TQThreadStorage can only store pointers.</em>
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<p> The <a href="#setLocalData">setLocalData</a>() function stores a single thread-specific value
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for the calling thread. The data can be accessed later using the
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<a href="#localData">localData</a>() functions. TQThreadStorage takes ownership of the
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data (which must be created on the heap with <em>new</em>) and deletes
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it when the thread exits (either normally or via termination).
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<p> The <a href="#hasLocalData">hasLocalData</a>() function allows the programmer to determine if
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data has previously been set using the setLocalData() function.
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This is useful for lazy initializiation.
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<p> For example, the following code uses TQThreadStorage to store a
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single cache for each thread that calls the <em>cacheObject()</em> and
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<em>removeFromCache()</em> functions. The cache is automatically
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deleted when the calling thread exits (either normally or via
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termination).
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<p> <pre>
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TQThreadStorage<TQCache<SomeClass> *> caches;
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void cacheObject( const <a href="ntqstring.html">TQString</a> &key, SomeClass *object )
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{
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if ( ! caches.hasLocalData() )
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caches.setLocalData( new <a href="ntqcache.html">TQCache</a><SomeClass> );
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caches.localData()->insert( key, object );
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}
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void removeFromCache( const <a href="ntqstring.html">TQString</a> &key )
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{
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if ( ! caches.hasLocalData() )
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return; // nothing to do
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caches.localData()->remove( key );
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}
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</pre>
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<p> <h3> Caveats
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</h3>
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<a name="1"></a><p> <ul>
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<p> <li> As noted above, TQThreadStorage can only store pointers due to
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compiler limitations. Support for value-based objects will be
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added when the majority of compilers are able to support partial
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template specialization.
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<p> <li> The <a href="#~TQThreadStorage">destructor</a> does <em>not</em>
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delete per-thread data. TQThreadStorage only deletes per-thread
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data when the thread exits or when <a href="#setLocalData">setLocalData</a>() is called
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multiple times.
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<p> <li> TQThreadStorage can only be used with threads started with
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<a href="ntqthread.html">TQThread</a>. It <em>cannot</em> be used with threads started with
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platform-specific APIs.
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<p> <li> As a corollary to the above, platform-specific APIs cannot be
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used to exit or terminate a TQThread using TQThreadStorage. Doing so
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will cause all per-thread data to be leaked. See <a href="ntqthread.html#exit">TQThread::exit</a>()
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and <a href="ntqthread.html#terminate">TQThread::terminate</a>().
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<p> <li> TQThreadStorage <em>can</em> be used to store data for the <em>main()</em>
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thread <em>after</em> <a href="ntqapplication.html">TQApplication</a> has been constructed. TQThreadStorage
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deletes all data set for the <em>main()</em> thread when TQApplication is
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destroyed, regardless of whether or not the <em>main()</em> thread has
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actually finished.
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<p> <li> The implementation of TQThreadStorage limits the total number of
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TQThreadStorage objects to 256. An unlimited number of threads
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can store per-thread data in each TQThreadStorage object.
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<p> </ul>
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<p>See also <a href="environment.html">Environment Classes</a> and <a href="thread.html">Threading</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="TQThreadStorage"></a>TQThreadStorage::TQThreadStorage ()
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</h3>
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<p> Constructs a new per-thread data storage object.
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<h3 class=fn><a name="~TQThreadStorage"></a>TQThreadStorage::~TQThreadStorage ()
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</h3>
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<p> Destroys the per-thread data storage object.
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<p> Note: The per-thread data stored is <em>not</em> deleted. Any data left
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in TQThreadStorage is leaked. Make sure that all threads using
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TQThreadStorage have exited before deleting the TQThreadStorage.
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<p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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<h3 class=fn>bool <a name="hasLocalData"></a>TQThreadStorage::hasLocalData () const
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</h3>
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<p> Returns TRUE if the calling thread has non-zero data available;
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otherwise returns FALSE.
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<p> <p>See also <a href="#localData">localData</a>().
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<h3 class=fn>T & <a name="localData"></a>TQThreadStorage::localData ()
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</h3>
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<p> Returns a reference to the data that was set by the calling
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thread.
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<p> Note: TQThreadStorage can only store pointers. This function
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returns a <em>reference</em> to the pointer that was set by the calling
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thread. The value of this reference is 0 if no data was set by
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the calling thread,
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<p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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<h3 class=fn>T <a name="localData-2"></a>TQThreadStorage::localData () const
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</h3>
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This is an overloaded member function, provided for convenience. It behaves essentially like the above function.
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<p> Returns a copy of the data that was set by the calling thread.
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<p> Note: TQThreadStorage can only store pointers. This function
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returns a pointer to the data that was set by the calling thread.
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If no data was set by the calling thread, this function returns 0.
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<p> <p>See also <a href="#hasLocalData">hasLocalData</a>().
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<h3 class=fn>void <a name="setLocalData"></a>TQThreadStorage::setLocalData ( T data )
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</h3>
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<p> Sets the local data for the calling thread to <em>data</em>. It can be
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accessed later using the <a href="#localData">localData</a>() functions.
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<p> If <em>data</em> is 0, this function deletes the previous data (if
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any) and returns immediately.
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<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
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(either normally or via termination) or when <a href="#setLocalData">setLocalData</a>() is
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called again.
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<p> Note: TQThreadStorage can only store pointers. The <em>data</em>
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argument must be either a pointer to an object created on the heap
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(i.e. using <em>new</em>) or 0. You should not delete <em>data</em>
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yourself; TQThreadStorage takes ownership and will delete the <em>data</em> itself.
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<p> <p>See also <a href="#localData">localData</a>() and <a href="#hasLocalData">hasLocalData</a>().
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<hr><p>
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This file is part of the <a href="index.html">TQt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>TQt 3.3.8</div>
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