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  17     "><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="bk01pt03ch18s02.html" title="Semantics"><link rel="next" href="bk01pt03ch18s04.html" title="Design"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><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="bk01pt03ch18s02.html">Prev</a> </td><th width="60%" align="center">Chapter 18. Parallel Mode</th><td width="20%" 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" style="clear: both"><a name="manual.ext.parallel_mode.using"></a>Using</h2></div></div></div><div class="section" title="Prerequisite Compiler Flags"><div class="titlepage"><div><div><h3 class="title"><a name="parallel_mode.using.prereq_flags"></a>Prerequisite Compiler Flags</h3></div></div></div><p>
  18   Any use of parallel functionality requires additional compiler
  19   and runtime support, in particular support for OpenMP. Adding this support is
  20   not difficult: just compile your application with the compiler
  21   flag <code class="literal">-fopenmp</code>. This will link
  22   in <code class="code">libgomp</code>, the
  23   OpenMP <a class="link" href="http://gcc.gnu.org/onlinedocs/libgomp/" target="_top">GNU implementation</a>,
  24   whose presence is mandatory.
  25 </p><p>
  26 In addition, hardware that supports atomic operations and a compiler
  27   capable of producing atomic operations is mandatory: GCC defaults to no
  28   support for atomic operations on some common hardware
  29   architectures. Activating atomic operations may require explicit
  30   compiler flags on some targets (like sparc and x86), such
  31   as <code class="literal">-march=i686</code>,
  32   <code class="literal">-march=native</code> or <code class="literal">-mcpu=v9</code>. See
  33   the GCC manual for more information.
  34 </p></div><div class="section" title="Using Parallel Mode"><div class="titlepage"><div><div><h3 class="title"><a name="parallel_mode.using.parallel_mode"></a>Using Parallel Mode</h3></div></div></div><p>
  35   To use the libstdc++ parallel mode, compile your application with
  36   the prerequisite flags as detailed above, and in addition
  37   add <code class="constant">-D_GLIBCXX_PARALLEL</code>. This will convert all
  38   use of the standard (sequential) algorithms to the appropriate parallel
  39   equivalents. Please note that this doesn't necessarily mean that
  40   everything will end up being executed in a parallel manner, but
  41   rather that the heuristics and settings coded into the parallel
  42   versions will be used to determine if all, some, or no algorithms
  43   will be executed using parallel variants.
  44 </p><p>Note that the <code class="constant">_GLIBCXX_PARALLEL</code> define may change the
  45   sizes and behavior of standard class templates such as
  46   <code class="function">std::search</code>, and therefore one can only link code
  47   compiled with parallel mode and code compiled without parallel mode
  48   if no instantiation of a container is passed between the two
  49   translation units. Parallel mode functionality has distinct linkage,
  50   and cannot be confused with normal mode symbols.
  51 </p></div><div class="section" title="Using Specific Parallel Components"><div class="titlepage"><div><div><h3 class="title"><a name="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
  52   only specific algorithms need to be parallel-aware, individual
  53   parallel algorithms can be made available explicitly. These
  54   parallel algorithms are functionally equivalent to the standard
  55   drop-in algorithms used in parallel mode, but they are available in
  56   a separate namespace as GNU extensions and may be used in programs
  57   compiled with either release mode or with parallel mode.
  58 </p><p>An example of using a parallel version
  59 of <code class="function">std::sort</code>, but no other parallel algorithms, is:
  60 </p><pre class="programlisting">
  61 #include &lt;vector&gt;
  62 #include &lt;parallel/algorithm&gt;
  63
  64 int main()
  65 {
  66   std::vector&lt;int&gt; v(100);
  67
  68   // ...
  69
  70   // Explicitly force a call to parallel sort.
  71   __gnu_parallel::sort(v.begin(), v.end());
  72   return 0;
  73 }
  74 </pre><p>
  75 Then compile this code with the prerequisite compiler flags
  76 (<code class="literal">-fopenmp</code> and any necessary architecture-specific
  77 flags for atomic operations.)
  78 </p><p> The following table provides the names and headers of all the
  79   parallel algorithms that can be used in a similar manner:
  80 </p><div class="table"><a name="id632987"></a><p class="title"><b>Table 18.1. Parallel Algorithms</b></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="bk01pt03ch18s02.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 accesskey="n" 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