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diff src/fftw-3.3.5/doc/html/Thread-safety.html @ 42:2cd0e3b3e1fd
Current fftw source
| author | Chris Cannam |
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| date | Tue, 18 Oct 2016 13:40:26 +0100 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/fftw-3.3.5/doc/html/Thread-safety.html Tue Oct 18 13:40:26 2016 +0100 @@ -0,0 +1,141 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This manual is for FFTW +(version 3.3.5, 30 July 2016). + +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. --> +<!-- Created by GNU Texinfo 5.2, http://www.gnu.org/software/texinfo/ --> +<head> +<title>FFTW 3.3.5: Thread safety</title> + +<meta name="description" content="FFTW 3.3.5: Thread safety"> +<meta name="keywords" content="FFTW 3.3.5: Thread safety"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" rel="up" title="Multi-threaded FFTW"> +<link href="Distributed_002dmemory-FFTW-with-MPI.html#Distributed_002dmemory-FFTW-with-MPI" rel="next" title="Distributed-memory FFTW with MPI"> +<link href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" rel="prev" title="How Many Threads to Use?"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Thread-safety"></a> +<div class="header"> +<p> +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> [<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> +</div> +<hr> +<a name="Thread-safety-1"></a> +<h3 class="section">5.4 Thread safety</h3> + +<a name="index-threads-1"></a> +<a name="index-OpenMP-3"></a> +<a name="index-thread-safety-1"></a> +<p>Users writing multi-threaded programs (including OpenMP) must concern +themselves with the <em>thread safety</em> of the libraries they +use—that is, whether it is safe to call routines in parallel from +multiple threads. FFTW can be used in such an environment, but some +care must be taken because the planner routines share data +(e.g. wisdom and trigonometric tables) between calls and plans. +</p> +<p>The upshot is that the only thread-safe (re-entrant) routine in FFTW is +<code>fftw_execute</code> (and the new-array variants thereof). All other routines +(e.g. the planner) should only be called from one thread at a time. So, +for example, you can wrap a semaphore lock around any calls to the +planner; even more simply, you can just create all of your plans from +one thread. We do not think this should be an important restriction +(FFTW is designed for the situation where the only performance-sensitive +code is the actual execution of the transform), and the benefits of +shared data between plans are great. +</p> +<p>Note also that, since the plan is not modified by <code>fftw_execute</code>, +it is safe to execute the <em>same plan</em> in parallel by multiple +threads. However, since a given plan operates by default on a fixed +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. +</p> +<p>(Users should note that these comments only apply to programs using +shared-memory threads or OpenMP. Parallelism using MPI or forked processes +involves a separate address-space and global variables for each process, +and is not susceptible to problems of this sort.) +</p> +<p>If you are configured FFTW with the <code>--enable-debug</code> or +<code>--enable-debug-malloc</code> flags (see <a href="Installation-on-Unix.html#Installation-on-Unix">Installation on Unix</a>), +then <code>fftw_execute</code> is not thread-safe. These flags are not +documented because they are intended only for developing +and debugging FFTW, but if you must use <code>--enable-debug</code> then you +should also specifically pass <code>--disable-debug-malloc</code> for +<code>fftw_execute</code> to be thread-safe. +</p> +<p>Starting from FFTW-3.3.5, FFTW supports a new API to make the +planner thread-safe: +</p><div class="example"> +<pre class="example">void fftw_make_planner_thread_safe(void); +</pre></div> +<a name="index-fftw_005fmake_005fplanner_005fthread_005fsafe"></a> + +<p>This call installs a hook that wraps a lock around all planner calls. +This API is meant for “applications” that use “plugins” in multiple +threads, where each “plugin” calls single-threaded FFTW but is unaware +of the other “plugins” doing the same thing at the same time. In this +case, the “application” calls <code>fftw_make_planner_thread_safe()</code> +at the beginning to protect “plugins” from each other. +</p><hr> +<div class="header"> +<p> +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> [<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> +</div> + + + +</body> +</html>