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<!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-NS Stylesheets V1.78.1" /><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>
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Any use of parallel functionality requires additional compiler
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and runtime support, in particular support for OpenMP. Adding this support is
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not difficult: just compile your application with the compiler
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flag <code class="literal">-fopenmp</code>. This will link
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in <code class="code">libgomp</code>, the
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<a class="link" href="http://gcc.gnu.org/onlinedocs/libgomp/" target="_top">GNU Offloading and
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Multi Processing Runtime Library</a>,
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whose presence is mandatory.
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</p><p>
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In addition, hardware that supports atomic operations and a compiler
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capable of producing atomic operations is mandatory: GCC defaults to no
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support for atomic operations on some common hardware
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architectures. Activating atomic operations may require explicit
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compiler flags on some targets (like sparc and x86), such
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as <code class="literal">-march=i686</code>,
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<code class="literal">-march=native</code> or <code class="literal">-mcpu=v9</code>. See
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the GCC manual for more information.
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</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>
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To use the libstdc++ parallel mode, compile your application with
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the prerequisite flags as detailed above, and in addition
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add <code class="constant">-D_GLIBCXX_PARALLEL</code>. This will convert all
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use of the standard (sequential) algorithms to the appropriate parallel
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equivalents. Please note that this doesn't necessarily mean that
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everything will end up being executed in a parallel manner, but
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rather that the heuristics and settings coded into the parallel
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versions will be used to determine if all, some, or no algorithms
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will be executed using parallel variants.
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</p><p>Note that the <code class="constant">_GLIBCXX_PARALLEL</code> define may change the
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sizes and behavior of standard class templates such as
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<code class="function">std::search</code>, and therefore one can only link code
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compiled with parallel mode and code compiled without parallel mode
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if no instantiation of a container is passed between the two
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translation units. Parallel mode functionality has distinct linkage,
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and cannot be confused with normal mode symbols.
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</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
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only specific algorithms need to be parallel-aware, individual
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parallel algorithms can be made available explicitly. These
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parallel algorithms are functionally equivalent to the standard
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drop-in algorithms used in parallel mode, but they are available in
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a separate namespace as GNU extensions and may be used in programs
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compiled with either release mode or with parallel mode.
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</p><p>An example of using a parallel version
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of <code class="function">std::sort</code>, but no other parallel algorithms, is:
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</p><pre class="programlisting">
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#include <vector>
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#include <parallel/algorithm>
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int main()
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{
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std::vector<int> v(100);
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// ...
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// Explicitly force a call to parallel sort.
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__gnu_parallel::sort(v.begin(), v.end());
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return 0;
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}
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</pre><p>
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Then compile this code with the prerequisite compiler flags
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(<code class="literal">-fopenmp</code> and any necessary architecture-specific
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flags for atomic operations.)
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</p><p> The following table provides the names and headers of all the
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parallel algorithms that can be used in a similar manner:
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</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 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" href="parallel_mode_semantics.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="parallel_mode.html">Up</a></td><td width="40%" align="right"> <a 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