<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en_US" lang="en_US">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<!-- threads.qdoc -->
<title>Qt 4.8: Concurrent Programming</title>
<link rel="stylesheet" type="text/css" href="style/style.css" />
<script src="scripts/jquery.js" type="text/javascript"></script>
<script src="scripts/functions.js" type="text/javascript"></script>
<link rel="stylesheet" type="text/css" href="style/superfish.css" />
<link rel="stylesheet" type="text/css" href="style/narrow.css" />
<!--[if IE]>
<meta name="MSSmartTagsPreventParsing" content="true">
<meta http-equiv="imagetoolbar" content="no">
<![endif]-->
<!--[if lt IE 7]>
<link rel="stylesheet" type="text/css" href="style/style_ie6.css">
<![endif]-->
<!--[if IE 7]>
<link rel="stylesheet" type="text/css" href="style/style_ie7.css">
<![endif]-->
<!--[if IE 8]>
<link rel="stylesheet" type="text/css" href="style/style_ie8.css">
<![endif]-->
<script src="scripts/superfish.js" type="text/javascript"></script>
<script src="scripts/narrow.js" type="text/javascript"></script>
</head>
<body class="" onload="CheckEmptyAndLoadList();">
<div class="header" id="qtdocheader">
<div class="content">
<div id="nav-logo">
<a href="index.html">Home</a></div>
<a href="index.html" class="qtref"><span>Qt Reference Documentation</span></a>
<div id="narrowsearch"></div>
<div id="nav-topright">
<ul>
<li class="nav-topright-home"><a href="http://qt.digia.com/">Qt HOME</a></li>
<li class="nav-topright-dev"><a href="http://qt-project.org/">DEV</a></li>
<li class="nav-topright-doc nav-topright-doc-active"><a href="http://qt-project.org/doc/">
DOC</a></li>
<li class="nav-topright-blog"><a href="http://blog.qt.digia.com/">BLOG</a></li>
</ul>
</div>
<div id="shortCut">
<ul>
<li class="shortCut-topleft-inactive"><span><a href="index.html">Qt 4.8</a></span></li>
<li class="shortCut-topleft-active"><a href="http://qt-project.org/doc/">ALL VERSIONS </a></li>
</ul>
</div>
<ul class="sf-menu" id="narrowmenu">
<li><a href="#">API Lookup</a>
<ul>
<li><a href="classes.html">Class index</a></li>
<li><a href="functions.html">Function index</a></li>
<li><a href="modules.html">Modules</a></li>
<li><a href="namespaces.html">Namespaces</a></li>
<li><a href="qtglobal.html">Global Declarations</a></li>
<li><a href="qdeclarativeelements.html">QML elements</a></li>
</ul>
</li>
<li><a href="#">Qt Topics</a>
<ul>
<li><a href="qt-basic-concepts.html">Programming with Qt</a></li>
<li><a href="qtquick.html">Device UIs & Qt Quick</a></li>
<li><a href="qt-gui-concepts.html">UI Design with Qt</a></li>
<li><a href="supported-platforms.html">Supported Platforms</a></li>
<li><a href="technology-apis.html">Qt and Key Technologies</a></li>
<li><a href="best-practices.html">How-To's and Best Practices</a></li>
</ul>
</li>
<li><a href="#">Examples</a>
<ul>
<li><a href="all-examples.html">Examples</a></li>
<li><a href="tutorials.html">Tutorials</a></li>
<li><a href="demos.html">Demos</a></li>
<li><a href="qdeclarativeexamples.html">QML Examples</a></li>
</ul>
</li>
</ul>
</div>
</div>
<div class="wrapper">
<div class="hd">
<span></span>
</div>
<div class="bd group">
<div class="sidebar">
<div class="searchlabel">
Search index:</div>
<div class="search" id="sidebarsearch">
<form id="qtdocsearch" action="" onsubmit="return false;">
<fieldset>
<input type="text" name="searchstring" id="pageType" value="" />
<div id="resultdialog">
<a href="#" id="resultclose">Close</a>
<p id="resultlinks" class="all"><a href="#" id="showallresults">All</a> | <a href="#" id="showapiresults">API</a> | <a href="#" id="showarticleresults">Articles</a> | <a href="#" id="showexampleresults">Examples</a></p>
<p id="searchcount" class="all"><span id="resultcount"></span><span id="apicount"></span><span id="articlecount"></span><span id="examplecount"></span> results:</p>
<ul id="resultlist" class="all">
</ul>
</div>
</fieldset>
</form>
</div>
<div class="box first bottombar" id="lookup">
<h2 title="API Lookup"><span></span>
API Lookup</h2>
<div id="list001" class="list">
<ul id="ul001" >
<li class="defaultLink"><a href="classes.html">Class index</a></li>
<li class="defaultLink"><a href="functions.html">Function index</a></li>
<li class="defaultLink"><a href="modules.html">Modules</a></li>
<li class="defaultLink"><a href="namespaces.html">Namespaces</a></li>
<li class="defaultLink"><a href="qtglobal.html">Global Declarations</a></li>
<li class="defaultLink"><a href="qdeclarativeelements.html">QML elements</a></li>
</ul>
</div>
</div>
<div class="box bottombar" id="topics">
<h2 title="Qt Topics"><span></span>
Qt Topics</h2>
<div id="list002" class="list">
<ul id="ul002" >
<li class="defaultLink"><a href="qt-basic-concepts.html">Programming with Qt</a></li>
<li class="defaultLink"><a href="qtquick.html">Device UIs & Qt Quick</a></li>
<li class="defaultLink"><a href="qt-gui-concepts.html">UI Design with Qt</a></li>
<li class="defaultLink"><a href="supported-platforms.html">Supported Platforms</a></li>
<li class="defaultLink"><a href="technology-apis.html">Qt and Key Technologies</a></li>
<li class="defaultLink"><a href="best-practices.html">How-To's and Best Practices</a></li>
</ul>
</div>
</div>
<div class="box" id="examples">
<h2 title="Examples"><span></span>
Examples</h2>
<div id="list003" class="list">
<ul id="ul003">
<li class="defaultLink"><a href="all-examples.html">Examples</a></li>
<li class="defaultLink"><a href="tutorials.html">Tutorials</a></li>
<li class="defaultLink"><a href="demos.html">Demos</a></li>
<li class="defaultLink"><a href="qdeclarativeexamples.html">QML Examples</a></li>
</ul>
</div>
</div>
</div>
<div class="wrap">
<div class="toolbar">
<div class="breadcrumb toolblock">
<ul>
<li class="first"><a href="index.html">Home</a></li>
<!-- Breadcrumbs go here -->
<li>Concurrent Programming</li>
</ul>
</div>
<div class="toolbuttons toolblock">
<ul>
<li id="smallA" class="t_button">A</li>
<li id="medA" class="t_button active">A</li>
<li id="bigA" class="t_button">A</li>
<li id="print" class="t_button"><a href="javascript:this.print();">
<span>Print</span></a></li>
</ul>
</div>
</div>
<div class="content mainContent">
<link rel="prev" href="threads-qobject.html" />
<link rel="next" href="threads-modules.html" />
<p class="naviNextPrevious headerNavi">
<a class="prevPage" href="threads-qobject.html">Threads and QObjects</a>
<a class="nextPage" href="threads-modules.html">Thread-Support in Qt Modules</a>
</p><p/>
<h1 class="title">Concurrent Programming</h1>
<span class="subtitle"></span>
<!-- $$$threads-qtconcurrent.html-description -->
<div class="descr"> <a name="details"></a>
<a name="qtconcurrent-intro"></a><p>The <a href="qtconcurrent.html">QtConcurrent</a> namespace provides high-level APIs that make it possible to write multi-threaded programs without using low-level threading primitives such as mutexes, read-write locks, wait conditions, or semaphores. Programs written with <a href="qtconcurrent.html">QtConcurrent</a> automatically adjust the number of threads used according to the number of processor cores available. This means that applications written today will continue to scale when deployed on multi-core systems in the future.</p>
<p><a href="qtconcurrent.html">QtConcurrent</a> includes functional programming style APIs for parallel list processing, including a MapReduce and FilterReduce implementation for shared-memory (non-distributed) systems, and classes for managing asynchronous computations in GUI applications:</p>
<ul>
<li><a href="qtconcurrentmap.html#map">QtConcurrent::map</a>() applies a function to every item in a container, modifying the items in-place.</li>
<li><a href="qtconcurrentmap.html#mapped">QtConcurrent::mapped</a>() is like map(), except that it returns a new container with the modifications.</li>
<li><a href="qtconcurrentmap.html#mappedReduced">QtConcurrent::mappedReduced</a>() is like mapped(), except that the modified results are reduced or folded into a single result.</li>
<li><a href="qtconcurrentfilter.html#filter">QtConcurrent::filter</a>() removes all items from a container based on the result of a filter function.</li>
<li><a href="qtconcurrentfilter.html#filtered">QtConcurrent::filtered</a>() is like filter(), except that it returns a new container with the filtered results.</li>
<li><a href="qtconcurrentfilter.html#filteredReduced">QtConcurrent::filteredReduced</a>() is like filtered(), except that the filtered results are reduced or folded into a single result.</li>
<li><a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() runs a function in another thread.</li>
<li><a href="qfuture.html">QFuture</a> represents the result of an asynchronous computation.</li>
<li><a href="qfutureiterator.html">QFutureIterator</a> allows iterating through results available via <a href="qfuture.html">QFuture</a>.</li>
<li><a href="qfuturewatcher.html">QFutureWatcher</a> allows monitoring a <a href="qfuture.html">QFuture</a> using signals-and-slots.</li>
<li><a href="qfuturesynchronizer.html">QFutureSynchronizer</a> is a convenience class that automatically synchronizes several QFutures.</li>
</ul>
<p>Qt Concurrent supports several STL-compatible container and iterator types, but works best with Qt containers that have random-access iterators, such as <a href="qlist.html">QList</a> or <a href="qvector.html">QVector</a>. The map and filter functions accept both containers and begin/end iterators.</p>
<p>STL Iterator support overview:</p>
<table class="generic">
<thead><tr class="qt-style"><th >Iterator Type</th><th >Example classes</th><th >Support status</th></tr></thead>
<tr valign="top" class="odd"><td >Input Iterator</td><td ></td><td >Not Supported</td></tr>
<tr valign="top" class="even"><td >Output Iterator</td><td ></td><td >Not Supported</td></tr>
<tr valign="top" class="odd"><td >Forward Iterator</td><td >std::slist</td><td >Supported</td></tr>
<tr valign="top" class="even"><td >Bidirectional Iterator</td><td ><a href="qlinkedlist.html">QLinkedList</a>, std::list</td><td >Supported</td></tr>
<tr valign="top" class="odd"><td >Random Access Iterator</td><td ><a href="qlist.html">QList</a>, <a href="qvector.html">QVector</a>, std::vector</td><td >Supported and Recommended</td></tr>
</table>
<p>Random access iterators can be faster in cases where Qt Concurrent is iterating over a large number of lightweight items, since they allow skipping to any point in the container. In addition, using random access iterators allows Qt Concurrent to provide progress information trough <a href="qfuture.html#progressValue">QFuture::progressValue</a>() and QFutureWatcher:: progressValueChanged().</p>
<p>The non in-place modifying functions such as mapped() and filtered() makes a copy of the container when called. If you are using STL containers this copy operation might take some time, in this case we recommend specifying the begin and end iterators for the container instead.</p>
</div>
<!-- @@@threads-qtconcurrent.html -->
<p class="naviNextPrevious footerNavi">
<a class="prevPage" href="threads-qobject.html">Threads and QObjects</a>
<a class="nextPage" href="threads-modules.html">Thread-Support in Qt Modules</a>
</p>
</div>
</div>
</div>
<div class="ft">
<span></span>
</div>
</div>
<div class="footer">
<p>
<acronym title="Copyright">©</acronym> 2013 Digia Plc and/or its
subsidiaries. Documentation contributions included herein are the copyrights of
their respective owners.</p>
<br />
<p>
The documentation provided herein is licensed under the terms of the
<a href="http://www.gnu.org/licenses/fdl.html">GNU Free Documentation
License version 1.3</a> as published by the Free Software Foundation.</p>
<p>
Documentation sources may be obtained from <a href="http://www.qt-project.org">
www.qt-project.org</a>.</p>
<br />
<p>
Digia, Qt and their respective logos are trademarks of Digia Plc
in Finland and/or other countries worldwide. All other trademarks are property
of their respective owners. <a title="Privacy Policy"
href="http://en.gitorious.org/privacy_policy/">Privacy Policy</a></p>
</div>
<script src="scripts/functions.js" type="text/javascript"></script>
</body>
</html>
