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Add FFTW3
| author | Chris Cannam <cannam@all-day-breakfast.com> |
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| date | Wed, 20 Mar 2013 15:35:50 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.3/doc/html/Usage-of-Multi_002dthreaded-FFTW.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,132 @@ +<html lang="en"> +<head> +<title>Usage of Multi-threaded FFTW - FFTW 3.3.3</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="FFTW 3.3.3"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" title="Multi-threaded FFTW"> +<link rel="prev" href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware" title="Installation and Supported Hardware/Software"> +<link rel="next" href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" title="How Many Threads to Use?"> +<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for FFTW +(version 3.3.3, 25 November 2012). + +Copyright (C) 2003 Matteo Frigo. + +Copyright (C) 2003 Massachusetts Institute of Technology. + + Permission is granted to make and distribute verbatim copies of + this manual provided the copyright notice and this permission + notice are preserved on all copies. + + Permission is granted to copy and distribute modified versions of + this manual under the conditions for verbatim copying, provided + that the entire resulting derived work is distributed under the + terms of a permission notice identical to this one. + + Permission is granted to copy and distribute translations of this + manual into another language, under the above conditions for + modified versions, except that this permission notice may be + stated in a translation approved by the Free Software Foundation. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Usage-of-Multi-threaded-FFTW"></a> +<a name="Usage-of-Multi_002dthreaded-FFTW"></a> +<p> +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>, +Previous: <a rel="previous" accesskey="p" href="Installation-and-Supported-Hardware_002fSoftware.html#Installation-and-Supported-Hardware_002fSoftware">Installation and Supported Hardware/Software</a>, +Up: <a rel="up" accesskey="u" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a> +<hr> +</div> + +<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><a name="index-OpenMP-332"></a>First, programs using the parallel complex transforms should be linked +with <code>-lfftw3_threads -lfftw3 -lm</code> on Unix, or <code>-lfftw3_omp +-lfftw3 -lm</code> if you compiled with OpenMP. You will also need to link +with whatever library is responsible for threads on your system +(e.g. <code>-lpthread</code> on GNU/Linux) or include whatever compiler flag +enables OpenMP (e.g. <code>-fopenmp</code> with gcc). +<a name="index-linking-on-Unix-333"></a> + + <p>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-334"></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-335"></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><a name="index-OpenMP-336"></a>With OpenMP, to configure FFTW to use all of the currently running +OpenMP threads (set by <code>omp_set_num_threads(nthreads)</code> or by the +<code>OMP_NUM_THREADS</code> environment variable), you can do: +<code>fftw_plan_with_nthreads(omp_get_max_threads())</code>. (The ‘<samp><span class="samp">omp_</span></samp>’ +OpenMP functions are declared via <code>#include <omp.h></code>.) + + <p><a name="index-thread-safety-337"></a>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>. As described in +<a href="Thread-safety.html#Thread-safety">Thread safety</a>, plan <em>execution</em> is thread-safe, but plan +creation and destruction are <em>not</em>: you should create/destroy +plans only from a single thread, but can safely execute multiple plans +in parallel. + + <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-338"></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>. + +<!-- --> + </body></html> +