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Replace these with versions built using an older toolset (so as to avoid ABI compatibilities when linking on Ubuntu 14.04 for packaging purposes)
author Chris Cannam
date Fri, 07 Feb 2020 11:51:13 +0000
parents 2cd0e3b3e1fd
children
rev   line source
Chris@42 1 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
Chris@42 2 <html>
Chris@42 3 <!-- This manual is for FFTW
Chris@42 4 (version 3.3.5, 30 July 2016).
Chris@42 5
Chris@42 6 Copyright (C) 2003 Matteo Frigo.
Chris@42 7
Chris@42 8 Copyright (C) 2003 Massachusetts Institute of Technology.
Chris@42 9
Chris@42 10 Permission is granted to make and distribute verbatim copies of this
Chris@42 11 manual provided the copyright notice and this permission notice are
Chris@42 12 preserved on all copies.
Chris@42 13
Chris@42 14 Permission is granted to copy and distribute modified versions of this
Chris@42 15 manual under the conditions for verbatim copying, provided that the
Chris@42 16 entire resulting derived work is distributed under the terms of a
Chris@42 17 permission notice identical to this one.
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Chris@42 19 Permission is granted to copy and distribute translations of this manual
Chris@42 20 into another language, under the above conditions for modified versions,
Chris@42 21 except that this permission notice may be stated in a translation
Chris@42 22 approved by the Free Software Foundation. -->
Chris@42 23 <!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ -->
Chris@42 24 <head>
Chris@42 25 <title>FFTW 3.3.5: Thread safety</title>
Chris@42 26
Chris@42 27 <meta name="description" content="FFTW 3.3.5: Thread safety">
Chris@42 28 <meta name="keywords" content="FFTW 3.3.5: Thread safety">
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Chris@42 33 <link href="index.html#Top" rel="start" title="Top">
Chris@42 34 <link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index">
Chris@42 35 <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
Chris@42 36 <link href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" rel="up" title="Multi-threaded FFTW">
Chris@42 37 <link href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="next" title="Distributed-memory FFTW with MPI">
Chris@42 38 <link href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" rel="prev" title="How Many Threads to Use?">
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Chris@42 66 </style>
Chris@42 67
Chris@42 68
Chris@42 69 </head>
Chris@42 70
Chris@42 71 <body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
Chris@42 72 <a name="Thread-safety"></a>
Chris@42 73 <div class="header">
Chris@42 74 <p>
Chris@42 75 Previous: <a href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" accesskey="p" rel="prev">How Many Threads to Use?</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>
Chris@42 76 </div>
Chris@42 77 <hr>
Chris@42 78 <a name="Thread-safety-1"></a>
Chris@42 79 <h3 class="section">5.4 Thread safety</h3>
Chris@42 80
Chris@42 81 <a name="index-threads-1"></a>
Chris@42 82 <a name="index-OpenMP-3"></a>
Chris@42 83 <a name="index-thread-safety-1"></a>
Chris@42 84 <p>Users writing multi-threaded programs (including OpenMP) must concern
Chris@42 85 themselves with the <em>thread safety</em> of the libraries they
Chris@42 86 use&mdash;that is, whether it is safe to call routines in parallel from
Chris@42 87 multiple threads. FFTW can be used in such an environment, but some
Chris@42 88 care must be taken because the planner routines share data
Chris@42 89 (e.g. wisdom and trigonometric tables) between calls and plans.
Chris@42 90 </p>
Chris@42 91 <p>The upshot is that the only thread-safe (re-entrant) routine in FFTW is
Chris@42 92 <code>fftw_execute</code> (and the new-array variants thereof). All other routines
Chris@42 93 (e.g. the planner) should only be called from one thread at a time. So,
Chris@42 94 for example, you can wrap a semaphore lock around any calls to the
Chris@42 95 planner; even more simply, you can just create all of your plans from
Chris@42 96 one thread. We do not think this should be an important restriction
Chris@42 97 (FFTW is designed for the situation where the only performance-sensitive
Chris@42 98 code is the actual execution of the transform), and the benefits of
Chris@42 99 shared data between plans are great.
Chris@42 100 </p>
Chris@42 101 <p>Note also that, since the plan is not modified by <code>fftw_execute</code>,
Chris@42 102 it is safe to execute the <em>same plan</em> in parallel by multiple
Chris@42 103 threads. However, since a given plan operates by default on a fixed
Chris@42 104 array, you need to use one of the new-array execute functions (see <a href="New_002darray-Execute-Functions.html#New_002darray-Execute-Functions">New-array Execute Functions</a>) so that different threads compute the transform of different data.
Chris@42 105 </p>
Chris@42 106 <p>(Users should note that these comments only apply to programs using
Chris@42 107 shared-memory threads or OpenMP. Parallelism using MPI or forked processes
Chris@42 108 involves a separate address-space and global variables for each process,
Chris@42 109 and is not susceptible to problems of this sort.)
Chris@42 110 </p>
Chris@42 111 <p>If you are configured FFTW with the <code>--enable-debug</code> or
Chris@42 112 <code>--enable-debug-malloc</code> flags (see <a href="Installation-on-Unix.html#Installation-on-Unix">Installation on Unix</a>),
Chris@42 113 then <code>fftw_execute</code> is not thread-safe. These flags are not
Chris@42 114 documented because they are intended only for developing
Chris@42 115 and debugging FFTW, but if you must use <code>--enable-debug</code> then you
Chris@42 116 should also specifically pass <code>--disable-debug-malloc</code> for
Chris@42 117 <code>fftw_execute</code> to be thread-safe.
Chris@42 118 </p>
Chris@42 119 <p>Starting from FFTW-3.3.5, FFTW supports a new API to make the
Chris@42 120 planner thread-safe:
Chris@42 121 </p><div class="example">
Chris@42 122 <pre class="example">void fftw_make_planner_thread_safe(void);
Chris@42 123 </pre></div>
Chris@42 124 <a name="index-fftw_005fmake_005fplanner_005fthread_005fsafe"></a>
Chris@42 125
Chris@42 126 <p>This call installs a hook that wraps a lock around all planner calls.
Chris@42 127 This API is meant for &ldquo;applications&rdquo; that use &ldquo;plugins&rdquo; in multiple
Chris@42 128 threads, where each &ldquo;plugin&rdquo; calls single-threaded FFTW but is unaware
Chris@42 129 of the other &ldquo;plugins&rdquo; doing the same thing at the same time. In this
Chris@42 130 case, the &ldquo;application&rdquo; calls <code>fftw_make_planner_thread_safe()</code>
Chris@42 131 at the beginning to protect &ldquo;plugins&rdquo; from each other.
Chris@42 132 </p><hr>
Chris@42 133 <div class="header">
Chris@42 134 <p>
Chris@42 135 Previous: <a href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" accesskey="p" rel="prev">How Many Threads to Use?</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>
Chris@42 136 </div>
Chris@42 137
Chris@42 138
Chris@42 139
Chris@42 140 </body>
Chris@42 141 </html>