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First commit. VS2013, Codeblocks and Mac OSX configuration
author Geogaddi\David <d.m.ronan@qmul.ac.uk>
date Thu, 09 Jul 2015 01:12:16 +0100
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+<head>
+<title>Usage of Multi-threaded FFTW - FFTW 3.2.1</title>
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+<a name="Usage-of-Multi_002dthreaded-FFTW"></a>
+Next:&nbsp;<a rel="next" accesskey="n" href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f">How Many Threads to Use?</a>,
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+<hr>
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+
+<h3 class="section">5.2 Usage of Multi-threaded FFTW</h3>
+
+<p>Here, it is assumed that the reader is already familiar with the usage
+of the uniprocessor FFTW routines, described elsewhere in this manual. 
+We only describe what one has to change in order to use the
+multi-threaded routines.
+
+   <p>First, programs using the parallel complex transforms should be linked with
+<code>-lfftw3_threads -lfftw3 -lm</code> on Unix. You will also need to link
+with whatever library is responsible for threads on your system
+(e.g. <code>-lpthread</code> on GNU/Linux). 
+<a name="index-linking-on-Unix-321"></a>
+Second, before calling <em>any</em> FFTW routines, you should call the
+function:
+
+<pre class="example">     int fftw_init_threads(void);
+</pre>
+   <p><a name="index-fftw_005finit_005fthreads-322"></a>
+This function, which need only be called once, performs any one-time
+initialization required to use threads on your system.  It returns zero
+if there was some error (which should not happen under normal
+circumstances) and a non-zero value otherwise.
+
+   <p>Third, before creating a plan that you want to parallelize, you should
+call:
+
+<pre class="example">     void fftw_plan_with_nthreads(int nthreads);
+</pre>
+   <p><a name="index-fftw_005fplan_005fwith_005fnthreads-323"></a>
+The <code>nthreads</code> argument indicates the number of threads you want
+FFTW to use (or actually, the maximum number).  All plans subsequently
+created with any planner routine will use that many threads.  You can
+call <code>fftw_plan_with_nthreads</code>, create some plans, call
+<code>fftw_plan_with_nthreads</code> again with a different argument, and
+create some more plans for a new number of threads.  Plans already created
+before a call to <code>fftw_plan_with_nthreads</code> are unaffected.  If you
+pass an <code>nthreads</code> argument of <code>1</code> (the default), threads are
+disabled for subsequent plans.
+
+   <p>Given a plan, you then execute it as usual with
+<code>fftw_execute(plan)</code>, and the execution will use the number of
+threads specified when the plan was created.  When done, you destroy it
+as usual with <code>fftw_destroy_plan</code>.
+
+   <p>There is one additional routine: if you want to get rid of all memory
+and other resources allocated internally by FFTW, you can call:
+
+<pre class="example">     void fftw_cleanup_threads(void);
+</pre>
+   <p><a name="index-fftw_005fcleanup_005fthreads-324"></a>
+which is much like the <code>fftw_cleanup()</code> function except that it
+also gets rid of threads-related data.  You must <em>not</em> execute any
+previously created plans after calling this function.
+
+   <p>We should also mention one other restriction: if you save wisdom from a
+program using the multi-threaded FFTW, that wisdom <em>cannot be used</em>
+by a program using only the single-threaded FFTW (i.e. not calling
+<code>fftw_init_threads</code>).  See <a href="Words-of-Wisdom_002dSaving-Plans.html#Words-of-Wisdom_002dSaving-Plans">Words of Wisdom-Saving Plans</a>.
+
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