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2 <head>
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3 <title>Usage of Multi-threaded FFTW - FFTW 3.2.1</title>
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4 <meta http-equiv="Content-Type" content="text/html">
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5 <meta name="description" content="FFTW 3.2.1">
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7 <link title="Top" rel="start" href="index.html#Top">
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8 <link rel="up" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" title="Multi-threaded FFTW">
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9 <link rel="prev" href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware" title="Installation and Supported Hardware/Software">
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10 <link rel="next" href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" title="How Many Threads to Use?">
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11 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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12 <!--
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13 This manual is for FFTW
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14 (version 3.2.1, 5 February 2009).
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15
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16 Copyright (C) 2003 Matteo Frigo.
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17
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18 Copyright (C) 2003 Massachusetts Institute of Technology.
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19
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20 Permission is granted to make and distribute verbatim copies of
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21 this manual provided the copyright notice and this permission
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22 notice are preserved on all copies.
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23
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24 Permission is granted to copy and distribute modified versions of
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25 this manual under the conditions for verbatim copying, provided
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26 that the entire resulting derived work is distributed under the
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27 terms of a permission notice identical to this one.
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28
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29 Permission is granted to copy and distribute translations of this
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30 manual into another language, under the above conditions for
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31 modified versions, except that this permission notice may be
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32 stated in a translation approved by the Free Software Foundation.
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33 -->
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45 --></style>
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46 </head>
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47 <body>
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48 <div class="node">
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49 <p>
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50 <a name="Usage-of-Multi-threaded-FFTW"></a>
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51 <a name="Usage-of-Multi_002dthreaded-FFTW"></a>
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52 Next: <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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53 Previous: <a rel="previous" accesskey="p" href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware">Installation and Supported Hardware/Software</a>,
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54 Up: <a rel="up" accesskey="u" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a>
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55 <hr>
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56 </div>
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57
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58 <h3 class="section">5.2 Usage of Multi-threaded FFTW</h3>
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59
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60 <p>Here, it is assumed that the reader is already familiar with the usage
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61 of the uniprocessor FFTW routines, described elsewhere in this manual.
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62 We only describe what one has to change in order to use the
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63 multi-threaded routines.
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64
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65 <p>First, programs using the parallel complex transforms should be linked with
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66 <code>-lfftw3_threads -lfftw3 -lm</code> on Unix. You will also need to link
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67 with whatever library is responsible for threads on your system
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68 (e.g. <code>-lpthread</code> on GNU/Linux).
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69 <a name="index-linking-on-Unix-321"></a>
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70 Second, before calling <em>any</em> FFTW routines, you should call the
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71 function:
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72
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73 <pre class="example"> int fftw_init_threads(void);
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74 </pre>
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75 <p><a name="index-fftw_005finit_005fthreads-322"></a>
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76 This function, which need only be called once, performs any one-time
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77 initialization required to use threads on your system. It returns zero
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78 if there was some error (which should not happen under normal
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79 circumstances) and a non-zero value otherwise.
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80
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81 <p>Third, before creating a plan that you want to parallelize, you should
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82 call:
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83
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84 <pre class="example"> void fftw_plan_with_nthreads(int nthreads);
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85 </pre>
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86 <p><a name="index-fftw_005fplan_005fwith_005fnthreads-323"></a>
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87 The <code>nthreads</code> argument indicates the number of threads you want
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88 FFTW to use (or actually, the maximum number). All plans subsequently
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89 created with any planner routine will use that many threads. You can
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90 call <code>fftw_plan_with_nthreads</code>, create some plans, call
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91 <code>fftw_plan_with_nthreads</code> again with a different argument, and
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92 create some more plans for a new number of threads. Plans already created
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93 before a call to <code>fftw_plan_with_nthreads</code> are unaffected. If you
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94 pass an <code>nthreads</code> argument of <code>1</code> (the default), threads are
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95 disabled for subsequent plans.
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96
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97 <p>Given a plan, you then execute it as usual with
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98 <code>fftw_execute(plan)</code>, and the execution will use the number of
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99 threads specified when the plan was created. When done, you destroy it
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100 as usual with <code>fftw_destroy_plan</code>.
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101
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102 <p>There is one additional routine: if you want to get rid of all memory
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103 and other resources allocated internally by FFTW, you can call:
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104
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105 <pre class="example"> void fftw_cleanup_threads(void);
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106 </pre>
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107 <p><a name="index-fftw_005fcleanup_005fthreads-324"></a>
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108 which is much like the <code>fftw_cleanup()</code> function except that it
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109 also gets rid of threads-related data. You must <em>not</em> execute any
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110 previously created plans after calling this function.
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111
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112 <p>We should also mention one other restriction: if you save wisdom from a
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113 program using the multi-threaded FFTW, that wisdom <em>cannot be used</em>
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114 by a program using only the single-threaded FFTW (i.e. not calling
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115 <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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116
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117 <!-- -->
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118 </body></html>
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119
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