116Salm<?xml version="1.0" encoding="UTF-8" standalone="no"?> 2<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Using</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><meta name="keywords" content="C++, library, parallel" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="parallel_mode.html" title="Chapter��18.��Parallel Mode" /><link rel="prev" href="parallel_mode_semantics.html" title="Semantics" /><link rel="next" href="parallel_mode_design.html" title="Design" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Using</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="parallel_mode_semantics.html">Prev</a>��</td><th width="60%" align="center">Chapter��18.��Parallel Mode</th><td width="20%" align="right">��<a accesskey="n" href="parallel_mode_design.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="manual.ext.parallel_mode.using"></a>Using</h2></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.prereq_flags"></a>Prerequisite Compiler Flags</h3></div></div></div><p> 3 Any use of parallel functionality requires additional compiler 4 and runtime support, in particular support for OpenMP. Adding this support is 5 not difficult: just compile your application with the compiler 6 flag <code class="literal">-fopenmp</code>. This will link 7 in <code class="code">libgomp</code>, the 8 <a class="link" href="http://gcc.gnu.org/onlinedocs/libgomp/" target="_top">GNU Offloading and 9 Multi Processing Runtime Library</a>, 10 whose presence is mandatory. 11</p><p> 12In addition, hardware that supports atomic operations and a compiler 13 capable of producing atomic operations is mandatory: GCC defaults to no 14 support for atomic operations on some common hardware 15 architectures. Activating atomic operations may require explicit 16 compiler flags on some targets (like sparc and x86), such 17 as <code class="literal">-march=i686</code>, 18 <code class="literal">-march=native</code> or <code class="literal">-mcpu=v9</code>. See 19 the GCC manual for more information. 20</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.parallel_mode"></a>Using Parallel Mode</h3></div></div></div><p> 21 To use the libstdc++ parallel mode, compile your application with 22 the prerequisite flags as detailed above, and in addition 23 add <code class="constant">-D_GLIBCXX_PARALLEL</code>. This will convert all 24 use of the standard (sequential) algorithms to the appropriate parallel 25 equivalents. Please note that this doesn't necessarily mean that 26 everything will end up being executed in a parallel manner, but 27 rather that the heuristics and settings coded into the parallel 28 versions will be used to determine if all, some, or no algorithms 29 will be executed using parallel variants. 30</p><p>Note that the <code class="constant">_GLIBCXX_PARALLEL</code> define may change the 31 sizes and behavior of standard class templates such as 32 <code class="function">std::search</code>, and therefore one can only link code 33 compiled with parallel mode and code compiled without parallel mode 34 if no instantiation of a container is passed between the two 35 translation units. Parallel mode functionality has distinct linkage, 36 and cannot be confused with normal mode symbols. 37</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.specific"></a>Using Specific Parallel Components</h3></div></div></div><p>When it is not feasible to recompile your entire application, or 38 only specific algorithms need to be parallel-aware, individual 39 parallel algorithms can be made available explicitly. These 40 parallel algorithms are functionally equivalent to the standard 41 drop-in algorithms used in parallel mode, but they are available in 42 a separate namespace as GNU extensions and may be used in programs 43 compiled with either release mode or with parallel mode. 44</p><p>An example of using a parallel version 45of <code class="function">std::sort</code>, but no other parallel algorithms, is: 46</p><pre class="programlisting"> 47#include <vector> 48#include <parallel/algorithm> 49 50int main() 51{ 52 std::vector<int> v(100); 53 54 // ... 55 56 // Explicitly force a call to parallel sort. 57 __gnu_parallel::sort(v.begin(), v.end()); 58 return 0; 59} 60</pre><p> 61Then compile this code with the prerequisite compiler flags 62(<code class="literal">-fopenmp</code> and any necessary architecture-specific 63flags for atomic operations.) 64</p><p> The following table provides the names and headers of all the 65 parallel algorithms that can be used in a similar manner: 66</p><div class="table"><a id="table.parallel_algos"></a><p class="title"><strong>Table��18.1.��Parallel Algorithms</strong></p><div class="table-contents"><table class="table" summary="Parallel Algorithms" border="1"><colgroup><col align="left" class="c1" /><col align="left" class="c2" /><col align="left" class="c3" /><col align="left" class="c4" /></colgroup><thead><tr><th align="left">Algorithm</th><th align="left">Header</th><th align="left">Parallel algorithm</th><th align="left">Parallel header</th></tr></thead><tbody><tr><td align="left"><code class="function">std::accumulate</code></td><td align="left"><code class="filename">numeric</code></td><td align="left"><code class="function">__gnu_parallel::accumulate</code></td><td align="left"><code class="filename">parallel/numeric</code></td></tr><tr><td align="left"><code class="function">std::adjacent_difference</code></td><td align="left"><code class="filename">numeric</code></td><td align="left"><code class="function">__gnu_parallel::adjacent_difference</code></td><td align="left"><code class="filename">parallel/numeric</code></td></tr><tr><td align="left"><code class="function">std::inner_product</code></td><td align="left"><code class="filename">numeric</code></td><td align="left"><code class="function">__gnu_parallel::inner_product</code></td><td align="left"><code class="filename">parallel/numeric</code></td></tr><tr><td align="left"><code class="function">std::partial_sum</code></td><td align="left"><code class="filename">numeric</code></td><td align="left"><code class="function">__gnu_parallel::partial_sum</code></td><td align="left"><code class="filename">parallel/numeric</code></td></tr><tr><td align="left"><code class="function">std::adjacent_find</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::adjacent_find</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::count</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::count</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::count_if</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::count_if</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::equal</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::equal</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::find</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::find</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::find_if</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::find_if</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::find_first_of</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::find_first_of</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::for_each</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::for_each</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::generate</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::generate</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::generate_n</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::generate_n</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::lexicographical_compare</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::lexicographical_compare</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::mismatch</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::mismatch</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::search</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::search</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::search_n</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::search_n</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::transform</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::transform</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::replace</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::replace</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::replace_if</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::replace_if</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::max_element</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::max_element</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::merge</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::merge</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::min_element</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::min_element</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::nth_element</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::nth_element</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::partial_sort</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::partial_sort</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::partition</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::partition</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::random_shuffle</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::random_shuffle</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::set_union</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::set_union</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::set_intersection</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::set_intersection</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::set_symmetric_difference</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::set_symmetric_difference</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::set_difference</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::set_difference</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::sort</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::sort</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::stable_sort</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::stable_sort</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr><tr><td align="left"><code class="function">std::unique_copy</code></td><td align="left"><code class="filename">algorithm</code></td><td align="left"><code class="function">__gnu_parallel::unique_copy</code></td><td align="left"><code class="filename">parallel/algorithm</code></td></tr></tbody></table></div></div><br class="table-break" /></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" 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