<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> <!-- /home/espenr/tmp/qt-3.3.8-espenr-2499/qt-x11-free-3.3.8/src/tools/qthreadstorage_unix.cpp:163 --> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"> <title>TQThreadStorage Class</title> <style type="text/css"><!-- fn { margin-left: 1cm; text-indent: -1cm; } a:link { color: #004faf; text-decoration: none } a:visited { color: #672967; text-decoration: none } body { background: #ffffff; color: black; } --></style> </head> <body> <table border="0" cellpadding="0" cellspacing="0" width="100%"> <tr bgcolor="#E5E5E5"> <td valign=center> <a href="index.html"> <font color="#004faf">Home</font></a> | <a href="classes.html"> <font color="#004faf">All Classes</font></a> | <a href="mainclasses.html"> <font color="#004faf">Main Classes</font></a> | <a href="annotated.html"> <font color="#004faf">Annotated</font></a> | <a href="groups.html"> <font color="#004faf">Grouped Classes</font></a> | <a href="functions.html"> <font color="#004faf">Functions</font></a> </td> <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="qthreadstorage-h.html">ntqthreadstorage.h</a>></tt> <p><a href="qthreadstorage-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="ntqstring.html">TQString</a> &key, SomeClass *object ) { if ( ! caches.hasLocalData() ) caches.setLocalData( new <a href="ntqcache.html">TQCache</a><SomeClass> ); caches.localData()->insert( key, object ); } void removeFromCache( const <a href="ntqstring.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="ntqthread.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="ntqthread.html#exit">TQThread::exit</a>() and <a href="ntqthread.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>(). <!-- eof --> <hr><p> This file is part of the <a href="index.html">TQt toolkit</a>. Copyright © 1995-2007 <a href="http://www.trolltech.com/">Trolltech</a>. 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