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comparison Lib/fftw-3.2.1/doc/html/.svn/text-base/Thread-safety.html.svn-base @ 0:25bf17994ef1
First commit. VS2013, Codeblocks and Mac OSX configuration
| author | Geogaddi\David <d.m.ronan@qmul.ac.uk> |
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| date | Thu, 09 Jul 2015 01:12:16 +0100 |
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| 1 <html lang="en"> | |
| 2 <head> | |
| 3 <title>Thread safety - FFTW 3.2.1</title> | |
| 4 <meta http-equiv="Content-Type" content="text/html"> | |
| 5 <meta name="description" content="FFTW 3.2.1"> | |
| 6 <meta name="generator" content="makeinfo 4.8"> | |
| 7 <link title="Top" rel="start" href="index.html#Top"> | |
| 8 <link rel="up" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW" title="Multi-threaded FFTW"> | |
| 9 <link rel="prev" href="How-Many-Threads-to-Use_003f.html#How-Many-Threads-to-Use_003f" title="How Many Threads to Use?"> | |
| 10 <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> | |
| 11 <!-- | |
| 12 This manual is for FFTW | |
| 13 (version 3.2.1, 5 February 2009). | |
| 14 | |
| 15 Copyright (C) 2003 Matteo Frigo. | |
| 16 | |
| 17 Copyright (C) 2003 Massachusetts Institute of Technology. | |
| 18 | |
| 19 Permission is granted to make and distribute verbatim copies of | |
| 20 this manual provided the copyright notice and this permission | |
| 21 notice are preserved on all copies. | |
| 22 | |
| 23 Permission is granted to copy and distribute modified versions of | |
| 24 this manual under the conditions for verbatim copying, provided | |
| 25 that the entire resulting derived work is distributed under the | |
| 26 terms of a permission notice identical to this one. | |
| 27 | |
| 28 Permission is granted to copy and distribute translations of this | |
| 29 manual into another language, under the above conditions for | |
| 30 modified versions, except that this permission notice may be | |
| 31 stated in a translation approved by the Free Software Foundation. | |
| 32 --> | |
| 33 <meta http-equiv="Content-Style-Type" content="text/css"> | |
| 34 <style type="text/css"><!-- | |
| 35 pre.display { font-family:inherit } | |
| 36 pre.format { font-family:inherit } | |
| 37 pre.smalldisplay { font-family:inherit; font-size:smaller } | |
| 38 pre.smallformat { font-family:inherit; font-size:smaller } | |
| 39 pre.smallexample { font-size:smaller } | |
| 40 pre.smalllisp { font-size:smaller } | |
| 41 span.sc { font-variant:small-caps } | |
| 42 span.roman { font-family:serif; font-weight:normal; } | |
| 43 span.sansserif { font-family:sans-serif; font-weight:normal; } | |
| 44 --></style> | |
| 45 </head> | |
| 46 <body> | |
| 47 <div class="node"> | |
| 48 <p> | |
| 49 <a name="Thread-safety"></a> | |
| 50 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>, | |
| 51 Up: <a rel="up" accesskey="u" href="Multi_002dthreaded-FFTW.html#Multi_002dthreaded-FFTW">Multi-threaded FFTW</a> | |
| 52 <hr> | |
| 53 </div> | |
| 54 | |
| 55 <h3 class="section">5.4 Thread safety</h3> | |
| 56 | |
| 57 <p><a name="index-threads-327"></a><a name="index-thread-safety-328"></a>Users writing multi-threaded programs must concern themselves with the | |
| 58 <dfn>thread safety</dfn> of the libraries they use—that is, whether it is | |
| 59 safe to call routines in parallel from multiple threads. FFTW can be | |
| 60 used in such an environment, but some care must be taken because the | |
| 61 planner routines share data (e.g. wisdom and trigonometric tables) | |
| 62 between calls and plans. | |
| 63 | |
| 64 <p>The upshot is that the only thread-safe (re-entrant) routine in FFTW is | |
| 65 <code>fftw_execute</code> (and the new-array variants thereof). All other routines | |
| 66 (e.g. the planner) should only be called from one thread at a time. So, | |
| 67 for example, you can wrap a semaphore lock around any calls to the | |
| 68 planner; even more simply, you can just create all of your plans from | |
| 69 one thread. We do not think this should be an important restriction | |
| 70 (FFTW is designed for the situation where the only performance-sensitive | |
| 71 code is the actual execution of the transform), and the benefits of | |
| 72 shared data between plans are great. | |
| 73 | |
| 74 <p>Note also that, since the plan is not modified by <code>fftw_execute</code>, | |
| 75 it is safe to execute the <em>same plan</em> in parallel by multiple | |
| 76 threads. However, since a given plan operates by default on a fixed | |
| 77 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. | |
| 78 | |
| 79 <p>(Users should note that these comments only apply to programs using | |
| 80 shared-memory threads. Parallelism using MPI or forked processes | |
| 81 involves a separate address-space and global variables for each process, | |
| 82 and is not susceptible to problems of this sort.) | |
| 83 | |
| 84 <!-- ************************************************************ --> | |
| 85 </body></html> | |
| 86 |