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<title>Qt 4.8: <QtConcurrentRun> - Asynchronous Run</title>
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<li class="level1"><a href="#running-a-function-in-a-separate-thread">Running a Function in a Separate Thread</a></li>
<li class="level1"><a href="#passing-arguments-to-the-function">Passing Arguments to the Function</a></li>
<li class="level1"><a href="#returning-values-from-the-function">Returning Values from the Function</a></li>
<li class="level1"><a href="#additional-api-features">Additional API Features</a></li>
<li class="level2"><a href="#using-member-functions">Using Member Functions</a></li>
<li class="level2"><a href="#using-bound-function-arguments">Using Bound Function Arguments</a></li>
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<h1 class="title"><QtConcurrentRun> - Asynchronous Run</h1>
<span class="subtitle"></span>
<!-- $$$<QtConcurrentRun>-brief -->
<p>The <QtConcurrentRun> header provides a way to run a function in a separate thread. <a href="#details">More...</a></p>
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<a name="Functionsx"></a>
<h2>Functions</h2>
<table class="alignedsummary">
<tr><td class="memItemLeft topAlign rightAlign"> QFuture<T> </td><td class="memItemRight bottomAlign"><b><a href="qtconcurrentrun.html#run">run</a></b> ( Function <i>function</i>, ... )</td></tr>
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<!-- $$$<QtConcurrentRun>-description -->
<div class="descr"> <a name="details"></a>
<p>This function is a part of the <a href="threads-qtconcurrent.html">Qt Concurrent</a> framework.</p>
<p>The <a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() function runs a function in a separate thread. The return value of the function is made available through the <a href="qfuture.html">QFuture</a> API.</p>
<a name="running-a-function-in-a-separate-thread"></a>
<h2>Running a Function in a Separate Thread</h2>
<p>To run a function in another thread, use <a href="qtconcurrentrun.html#run">QtConcurrent::run</a>():</p>
<pre class="cpp"> <span class="keyword">extern</span> <span class="type">void</span> aFunction();
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type">void</span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(aFunction);</pre>
<p>This will run <i>aFunction</i> in a separate thread obtained from the default <a href="qthreadpool.html">QThreadPool</a>. You can use the <a href="qfuture.html">QFuture</a> and <a href="qfuturewatcher.html">QFutureWatcher</a> classes to monitor the status of the function.</p>
<a name="passing-arguments-to-the-function"></a>
<h2>Passing Arguments to the Function</h2>
<p>Passing arguments to the function is done by adding them to the <a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() call immediately after the function name. For example:</p>
<pre class="cpp"> <span class="keyword">extern</span> <span class="type">void</span> aFunctionWithArguments(<span class="type">int</span> arg1<span class="operator">,</span> <span class="type">double</span> arg2<span class="operator">,</span> <span class="keyword">const</span> <span class="type"><a href="qstring.html">QString</a></span> <span class="operator">&</span>string);
<span class="type">int</span> integer <span class="operator">=</span> <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>;
<span class="type">double</span> floatingPoint <span class="operator">=</span> <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>;
<span class="type"><a href="qstring.html">QString</a></span> string <span class="operator">=</span> <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>;
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type">void</span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(aFunctionWithArguments<span class="operator">,</span> integer<span class="operator">,</span> floatingPoint<span class="operator">,</span> string);</pre>
<p>A copy of each argument is made at the point where <a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() is called, and these values are passed to the thread when it begins executing the function. Changes made to the arguments after calling <a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() are <i>not</i> visible to the thread.</p>
<a name="returning-values-from-the-function"></a>
<h2>Returning Values from the Function</h2>
<p>Any return value from the function is available via <a href="qfuture.html">QFuture</a>:</p>
<pre class="cpp"> <span class="keyword">extern</span> <span class="type"><a href="qstring.html">QString</a></span> functionReturningAString();
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(functionReturningAString);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qstring.html">QString</a></span> result <span class="operator">=</span> future<span class="operator">.</span>result();</pre>
<p>As documented above, passing arguments is done like this:</p>
<pre class="cpp"> <span class="keyword">extern</span> <span class="type"><a href="qstring.html">QString</a></span> someFunction(<span class="keyword">const</span> <span class="type"><a href="qbytearray.html">QByteArray</a></span> <span class="operator">&</span>input);
<span class="type"><a href="qbytearray.html">QByteArray</a></span> bytearray <span class="operator">=</span> <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>;
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(someFunction<span class="operator">,</span> bytearray);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qstring.html">QString</a></span> result <span class="operator">=</span> future<span class="operator">.</span>result();</pre>
<p>Note that the <a href="qfuture.html#result">QFuture::result</a>() function blocks and waits for the result to become available. Use <a href="qfuturewatcher.html">QFutureWatcher</a> to get notification when the function has finished execution and the result is available.</p>
<a name="additional-api-features"></a>
<h2>Additional API Features</h2>
<a name="using-member-functions"></a>
<h3>Using Member Functions</h3>
<p><a href="qtconcurrentrun.html#run">QtConcurrent::run</a>() also accepts pointers to member functions. The first argument must be either a const reference or a pointer to an instance of the class. Passing by const reference is useful when calling const member functions; passing by pointer is useful for calling non-const member functions that modify the instance.</p>
<p>For example, calling <a href="qbytearray.html#split">QByteArray::split</a>() (a const member function) in a separate thread is done like this:</p>
<pre class="cpp"> <span class="comment">// call 'QList<QByteArray> QByteArray::split(char sep) const' in a separate thread</span>
<span class="type"><a href="qbytearray.html">QByteArray</a></span> bytearray <span class="operator">=</span> <span class="string">"hello world"</span>;
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type"><a href="qlist.html">QList</a></span><span class="operator"><</span><span class="type"><a href="qbytearray.html">QByteArray</a></span><span class="operator">></span> <span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(bytearray<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qbytearray.html">QByteArray</a></span><span class="operator">::</span>split<span class="operator">,</span> <span class="char">','</span>);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
<span class="type"><a href="qlist.html">QList</a></span><span class="operator"><</span><span class="type"><a href="qbytearray.html">QByteArray</a></span><span class="operator">></span> result <span class="operator">=</span> future<span class="operator">.</span>result();</pre>
<p>Calling a non-const member function is done like this:</p>
<pre class="cpp"> <span class="comment">// call 'void QImage::invertPixels(InvertMode mode)' in a separate thread</span>
<span class="type"><a href="qimage.html">QImage</a></span> image <span class="operator">=</span> <span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>;
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type">void</span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(<span class="operator">&</span>image<span class="operator">,</span> <span class="operator">&</span><span class="type"><a href="qimage.html">QImage</a></span><span class="operator">::</span>invertPixels<span class="operator">,</span> <span class="type"><a href="qimage.html">QImage</a></span><span class="operator">::</span>InvertRgba);
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span>
future<span class="operator">.</span>waitForFinished();
<span class="comment">// At this point, the pixels in 'image' have been inverted</span></pre>
<a name="using-bound-function-arguments"></a>
<h3>Using Bound Function Arguments</h3>
<p>Note that Qt does not provide support for bound functions. This is provided by 3rd party libraries like <a href="http://www.boost.org/libs/bind/bind.html">Boost</a> or <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf">C++ TR1 Library Extensions</a>.</p>
<p>You can use boost::bind() or std::tr1::bind() to <i>bind</i> a number of arguments to a function when called. There are number of reasons for doing this:</p>
<ul>
<li>To call a function that takes more than 5 arguments.</li>
<li>To simplify calling a function with constant arguments.</li>
<li>Changing the order of arguments.</li>
</ul>
<p>See the documentation for the relevant functions for details on how to use the bind API.</p>
<p>Calling a bound function is done like this:</p>
<pre class="cpp"> <span class="type">void</span> someFunction(<span class="type">int</span> arg1<span class="operator">,</span> <span class="type">double</span> arg2);
<span class="type"><a href="qfuture.html">QFuture</a></span><span class="operator"><</span><span class="type">void</span><span class="operator">></span> future <span class="operator">=</span> <span class="type"><a href="qtconcurrent.html">QtConcurrent</a></span><span class="operator">::</span>run(boost<span class="operator">::</span>bind(someFunction<span class="operator">,</span> <span class="number">1</span><span class="operator">,</span> <span class="number">2.0</span>));
<span class="operator">.</span><span class="operator">.</span><span class="operator">.</span></pre>
</div>
<!-- @@@<QtConcurrentRun> -->
<h2>Function Documentation</h2>
<!-- $$$run[overload1]$$$runFunction... -->
<h3 class="fn"><a name="run"></a><span class="type"><a href="qfuture.html">QFuture</a></span><<span class="type">T</span>> QtConcurrent::<span class="name">run</span> ( <span class="type">Function</span> <i>function</i>, ... )</h3>
<p>Runs <i>function</i> in a separate thread. The thread is taken from the global <a href="qthreadpool.html">QThreadPool</a>. Note that the function may not run immediately; the function will only be run when a thread is available.</p>
<p>T is the same type as the return value of <i>function</i>. Non-void return values can be accessed via the <a href="qfuture.html#result">QFuture::result</a>() function.</p>
<p>Note that the <a href="qfuture.html">QFuture</a> returned by QtConcurrent::run() does not support canceling, pausing, or progress reporting. The <a href="qfuture.html">QFuture</a> returned can only be used to query for the running/finished status and the return value of the function.</p>
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