Mercurial > hg > sv-dependency-builds
diff src/fftw-3.3.3/doc/html/Thread-safety.html @ 10:37bf6b4a2645
Add FFTW3
| author | Chris Cannam |
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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/Thread-safety.html Wed Mar 20 15:35:50 2013 +0000 @@ -0,0 +1,93 @@ +<html lang="en"> +<head> +<title>Thread safety - 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="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="Thread-safety"></a> +<p> +Previous: <a rel="previous" accesskey="p" href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f">How Many Threads to Use?</a>, +Up: <a rel="up" accesskey="u" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a> +<hr> +</div> + +<h3 class="section">5.4 Thread safety</h3> + +<p><a name="index-threads-341"></a><a name="index-OpenMP-342"></a><a name="index-thread-safety-343"></a>Users writing multi-threaded programs (including OpenMP) must concern +themselves with the <dfn>thread safety</dfn> 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>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>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>(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>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. + + </body></html> +