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Add FFTW 3.3.8 source, and a Linux build
author Chris Cannam <cannam@all-day-breakfast.com>
date Tue, 19 Nov 2019 14:52:55 +0000
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cannam@167 3 <!-- This manual is for FFTW
cannam@167 4 (version 3.3.8, 24 May 2018).
cannam@167 5
cannam@167 6 Copyright (C) 2003 Matteo Frigo.
cannam@167 7
cannam@167 8 Copyright (C) 2003 Massachusetts Institute of Technology.
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cannam@167 10 Permission is granted to make and distribute verbatim copies of this
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cannam@167 24 <head>
cannam@167 25 <title>FFTW 3.3.8: Usage of Multi-threaded FFTW</title>
cannam@167 26
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cannam@167 68 </head>
cannam@167 69
cannam@167 70 <body lang="en">
cannam@167 71 <a name="Usage-of-Multi_002dthreaded-FFTW"></a>
cannam@167 72 <div class="header">
cannam@167 73 <p>
cannam@167 74 Next: <a href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" accesskey="n" rel="next">How Many Threads to Use?</a>, Previous: <a href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware" accesskey="p" rel="prev">Installation and Supported Hardware/Software</a>, Up: <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" accesskey="u" rel="up">Multi-threaded FFTW</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
cannam@167 75 </div>
cannam@167 76 <hr>
cannam@167 77 <a name="Usage-of-Multi_002dthreaded-FFTW-1"></a>
cannam@167 78 <h3 class="section">5.2 Usage of Multi-threaded FFTW</h3>
cannam@167 79
cannam@167 80 <p>Here, it is assumed that the reader is already familiar with the usage
cannam@167 81 of the uniprocessor FFTW routines, described elsewhere in this manual.
cannam@167 82 We only describe what one has to change in order to use the
cannam@167 83 multi-threaded routines.
cannam@167 84 </p>
cannam@167 85 <a name="index-OpenMP-1"></a>
cannam@167 86 <p>First, programs using the parallel complex transforms should be linked
cannam@167 87 with <code>-lfftw3_threads -lfftw3 -lm</code> on Unix, or <code>-lfftw3_omp
cannam@167 88 -lfftw3 -lm</code> if you compiled with OpenMP. You will also need to link
cannam@167 89 with whatever library is responsible for threads on your system
cannam@167 90 (e.g. <code>-lpthread</code> on GNU/Linux) or include whatever compiler flag
cannam@167 91 enables OpenMP (e.g. <code>-fopenmp</code> with gcc).
cannam@167 92 <a name="index-linking-on-Unix"></a>
cannam@167 93 </p>
cannam@167 94
cannam@167 95 <p>Second, before calling <em>any</em> FFTW routines, you should call the
cannam@167 96 function:
cannam@167 97 </p>
cannam@167 98 <div class="example">
cannam@167 99 <pre class="example">int fftw_init_threads(void);
cannam@167 100 </pre></div>
cannam@167 101 <a name="index-fftw_005finit_005fthreads"></a>
cannam@167 102
cannam@167 103 <p>This function, which need only be called once, performs any one-time
cannam@167 104 initialization required to use threads on your system. It returns zero
cannam@167 105 if there was some error (which should not happen under normal
cannam@167 106 circumstances) and a non-zero value otherwise.
cannam@167 107 </p>
cannam@167 108 <p>Third, before creating a plan that you want to parallelize, you should
cannam@167 109 call:
cannam@167 110 </p>
cannam@167 111 <div class="example">
cannam@167 112 <pre class="example">void fftw_plan_with_nthreads(int nthreads);
cannam@167 113 </pre></div>
cannam@167 114 <a name="index-fftw_005fplan_005fwith_005fnthreads"></a>
cannam@167 115
cannam@167 116 <p>The <code>nthreads</code> argument indicates the number of threads you want
cannam@167 117 FFTW to use (or actually, the maximum number). All plans subsequently
cannam@167 118 created with any planner routine will use that many threads. You can
cannam@167 119 call <code>fftw_plan_with_nthreads</code>, create some plans, call
cannam@167 120 <code>fftw_plan_with_nthreads</code> again with a different argument, and
cannam@167 121 create some more plans for a new number of threads. Plans already created
cannam@167 122 before a call to <code>fftw_plan_with_nthreads</code> are unaffected. If you
cannam@167 123 pass an <code>nthreads</code> argument of <code>1</code> (the default), threads are
cannam@167 124 disabled for subsequent plans.
cannam@167 125 </p>
cannam@167 126 <a name="index-OpenMP-2"></a>
cannam@167 127 <p>With OpenMP, to configure FFTW to use all of the currently running
cannam@167 128 OpenMP threads (set by <code>omp_set_num_threads(nthreads)</code> or by the
cannam@167 129 <code>OMP_NUM_THREADS</code> environment variable), you can do:
cannam@167 130 <code>fftw_plan_with_nthreads(omp_get_max_threads())</code>. (The &lsquo;<samp>omp_</samp>&rsquo;
cannam@167 131 OpenMP functions are declared via <code>#include &lt;omp.h&gt;</code>.)
cannam@167 132 </p>
cannam@167 133 <a name="index-thread-safety"></a>
cannam@167 134 <p>Given a plan, you then execute it as usual with
cannam@167 135 <code>fftw_execute(plan)</code>, and the execution will use the number of
cannam@167 136 threads specified when the plan was created. When done, you destroy
cannam@167 137 it as usual with <code>fftw_destroy_plan</code>. As described in
cannam@167 138 <a href="Thread-safety.html#Thread-safety">Thread safety</a>, plan <em>execution</em> is thread-safe, but plan
cannam@167 139 creation and destruction are <em>not</em>: you should create/destroy
cannam@167 140 plans only from a single thread, but can safely execute multiple plans
cannam@167 141 in parallel.
cannam@167 142 </p>
cannam@167 143 <p>There is one additional routine: if you want to get rid of all memory
cannam@167 144 and other resources allocated internally by FFTW, you can call:
cannam@167 145 </p>
cannam@167 146 <div class="example">
cannam@167 147 <pre class="example">void fftw_cleanup_threads(void);
cannam@167 148 </pre></div>
cannam@167 149 <a name="index-fftw_005fcleanup_005fthreads"></a>
cannam@167 150
cannam@167 151 <p>which is much like the <code>fftw_cleanup()</code> function except that it
cannam@167 152 also gets rid of threads-related data. You must <em>not</em> execute any
cannam@167 153 previously created plans after calling this function.
cannam@167 154 </p>
cannam@167 155 <p>We should also mention one other restriction: if you save wisdom from a
cannam@167 156 program using the multi-threaded FFTW, that wisdom <em>cannot be used</em>
cannam@167 157 by a program using only the single-threaded FFTW (i.e. not calling
cannam@167 158 <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>.
cannam@167 159 </p>
cannam@167 160 <hr>
cannam@167 161 <div class="header">
cannam@167 162 <p>
cannam@167 163 Next: <a href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" accesskey="n" rel="next">How Many Threads to Use?</a>, Previous: <a href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware" accesskey="p" rel="prev">Installation and Supported Hardware/Software</a>, Up: <a href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" accesskey="u" rel="up">Multi-threaded FFTW</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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