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<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Using</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" C++ , library , parallel "/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.html" title="The GNU C++ Library"/><link rel="up" href="parallel_mode.html" title="Chapter 18. Parallel Mode"/><link rel="prev" href="bk01pt03ch18s02.html" title="Semantics"/><link rel="next" href="bk01pt03ch18s04.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 align="left"><a accesskey="p" href="bk01pt03ch18s02.html">Prev</a> </td><th width="60%" align="center">Chapter 18. Parallel Mode</th><td align="right"> <a accesskey="n" href="bk01pt03ch18s04.html">Next</a></td></tr></table><hr/></div><div class="section" title="Using"><div class="titlepage"><div><div><h2 class="title"><a id="manual.ext.parallel_mode.using"/>Using</h2></div></div></div><div class="section" title="Prerequisite Compiler Flags"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.prereq_flags"/>Prerequisite Compiler Flags</h3></div></div></div><p>
Any use of parallel functionality requires additional compiler
and runtime support, in particular support for OpenMP. Adding this support is
not difficult: just compile your application with the compiler
flag <code class="literal">-fopenmp</code>. This will link
in <code class="code">libgomp</code>, the GNU
OpenMP <a class="link" href="http://gcc.gnu.org/onlinedocs/libgomp">implementation</a>,
whose presence is mandatory.
</p><p>
In addition, hardware that supports atomic operations and a compiler
capable of producing atomic operations is mandatory: GCC defaults to no
support for atomic operations on some common hardware
architectures. Activating atomic operations may require explicit
compiler flags on some targets (like sparc and x86), such
as <code class="literal">-march=i686</code>,
<code class="literal">-march=native</code> or <code class="literal">-mcpu=v9</code>. See
the GCC manual for more information.
</p></div><div class="section" title="Using Parallel Mode"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.parallel_mode"/>Using Parallel Mode</h3></div></div></div><p>
To use the libstdc++ parallel mode, compile your application with
the prerequisite flags as detailed above, and in addition
add <code class="constant">-D_GLIBCXX_PARALLEL</code>. This will convert all
use of the standard (sequential) algorithms to the appropriate parallel
equivalents. Please note that this doesn't necessarily mean that
everything will end up being executed in a parallel manner, but
rather that the heuristics and settings coded into the parallel
versions will be used to determine if all, some, or no algorithms
will be executed using parallel variants.
</p><p>Note that the <code class="constant">_GLIBCXX_PARALLEL</code> define may change the
sizes and behavior of standard class templates such as
<code class="function">std::search</code>, and therefore one can only link code
compiled with parallel mode and code compiled without parallel mode
if no instantiation of a container is passed between the two
translation units. Parallel mode functionality has distinct linkage,
and cannot be confused with normal mode symbols.
</p></div><div class="section" title="Using Specific Parallel Components"><div class="titlepage"><div><div><h3 class="title"><a id="parallel_mode.using.specific"/>Using Specific Parallel Components</h3></div></div></div><p>When it is not feasible to recompile your entire application, or
only specific algorithms need to be parallel-aware, individual
parallel algorithms can be made available explicitly. These
parallel algorithms are functionally equivalent to the standard
drop-in algorithms used in parallel mode, but they are available in
a separate namespace as GNU extensions and may be used in programs
compiled with either release mode or with parallel mode.
</p><p>An example of using a parallel version
of <code class="function">std::sort</code>, but no other parallel algorithms, is:
</p><pre class="programlisting">
#include <vector>
#include <parallel/algorithm>
int main()
{
std::vector<int> v(100);
// ...
// Explicitly force a call to parallel sort.
__gnu_parallel::sort(v.begin(), v.end());
return 0;
}
</pre><p>
Then compile this code with the prerequisite compiler flags
(<code class="literal">-fopenmp</code> and any necessary architecture-specific
flags for atomic operations.)
</p><p> The following table provides the names and headers of all the
parallel algorithms that can be used in a similar manner:
</p><div class="table"><a id="id484380"/><p class="title"><strong>Table 18.1. Parallel Algorithms</strong></p><div class="table-contents"><table summary="Parallel Algorithms" border="1"><colgroup><col style="text-align: left" class="c1"/><col style="text-align: left" class="c2"/><col style="text-align: left" class="c3"/><col style="text-align: left" class="c4"/></colgroup><thead><tr><th style="text-align: left">Algorithm</th><th style="text-align: left">Header</th><th style="text-align: left">Parallel algorithm</th><th style="text-align: left">Parallel header</th></tr></thead><tbody><tr><td style="text-align: left"><code class="function">std::accumulate</code></td><td style="text-align: left"><code class="filename">numeric</code></td><td style="text-align: left"><code class="function">__gnu_parallel::accumulate</code></td><td style="text-align: left"><code class="filename">parallel/numeric</code></td></tr><tr><td style="text-align: left"><code class="function">std::adjacent_difference</code></td><td style="text-align: left"><code class="filename">numeric</code></td><td style="text-align: left"><code class="function">__gnu_parallel::adjacent_difference</code></td><td style="text-align: left"><code class="filename">parallel/numeric</code></td></tr><tr><td style="text-align: left"><code class="function">std::inner_product</code></td><td style="text-align: left"><code class="filename">numeric</code></td><td style="text-align: left"><code class="function">__gnu_parallel::inner_product</code></td><td style="text-align: left"><code class="filename">parallel/numeric</code></td></tr><tr><td style="text-align: left"><code class="function">std::partial_sum</code></td><td style="text-align: left"><code class="filename">numeric</code></td><td style="text-align: left"><code class="function">__gnu_parallel::partial_sum</code></td><td style="text-align: left"><code class="filename">parallel/numeric</code></td></tr><tr><td style="text-align: left"><code class="function">std::adjacent_find</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::adjacent_find</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::count</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::count</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::count_if</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::count_if</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::equal</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::equal</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::find</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::find</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::find_if</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::find_if</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::find_first_of</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::find_first_of</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::for_each</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::for_each</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::generate</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::generate</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::generate_n</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::generate_n</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::lexicographical_compare</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::lexicographical_compare</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::mismatch</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::mismatch</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::search</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::search</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::search_n</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::search_n</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::transform</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::transform</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::replace</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::replace</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::replace_if</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::replace_if</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::max_element</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::max_element</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::merge</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::merge</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::min_element</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::min_element</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::nth_element</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::nth_element</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::partial_sort</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::partial_sort</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::partition</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::partition</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::random_shuffle</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::random_shuffle</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::set_union</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::set_union</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::set_intersection</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::set_intersection</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::set_symmetric_difference</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::set_symmetric_difference</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::set_difference</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::set_difference</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::sort</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::sort</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::stable_sort</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::stable_sort</code></td><td style="text-align: left"><code class="filename">parallel/algorithm</code></td></tr><tr><td style="text-align: left"><code class="function">std::unique_copy</code></td><td style="text-align: left"><code class="filename">algorithm</code></td><td style="text-align: left"><code class="function">__gnu_parallel::unique_copy</code></td><td style="text-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 align="left"><a accesskey="p" href="bk01pt03ch18s02.html">Prev</a> </td><td align="center"><a accesskey="u" href="parallel_mode.html">Up</a></td><td align="right"> <a accesskey="n" href="bk01pt03ch18s04.html">Next</a></td></tr><tr><td align="left" valign="top">Semantics </td><td align="center"><a accesskey="h" href="../spine.html">Home</a></td><td align="right" valign="top"> Design</td></tr></table></div></body></html>