Using

Using
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Prerequisite Compiler Flags

+ 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 -fopenmp. This will link + in libgomp, the GNU + OpenMP implementation, + whose presence is mandatory. +

+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 -march=i686, + -march=native or -mcpu=v9. See + the GCC manual for more information. +

Using Parallel Mode

+ To use the libstdc++ parallel mode, compile your application with + the prerequisite flags as detailed above, and in addition + add -D_GLIBCXX_PARALLEL. 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. +

Note that the _GLIBCXX_PARALLEL define may change the + sizes and behavior of standard class templates such as + std::search, 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. +

Using Specific Parallel Components

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. +

An example of using a parallel version +of std::sort, but no other parallel algorithms, is: +

+#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;
+}
+

+Then compile this code with the prerequisite compiler flags +(-fopenmp and any necessary architecture-specific +flags for atomic operations.) +

The following table provides the names and headers of all the + parallel algorithms that can be used in a similar manner: +

Table 18.1. Parallel Algorithms

Algorithm	Header	Parallel algorithm	Parallel header
`std::accumulate`	`numeric`	`__gnu_parallel::accumulate`	`parallel/numeric`
`std::adjacent_difference`	`numeric`	`__gnu_parallel::adjacent_difference`	`parallel/numeric`
`std::inner_product`	`numeric`	`__gnu_parallel::inner_product`	`parallel/numeric`
`std::partial_sum`	`numeric`	`__gnu_parallel::partial_sum`	`parallel/numeric`
`std::adjacent_find`	`algorithm`	`__gnu_parallel::adjacent_find`	`parallel/algorithm`
`std::count`	`algorithm`	`__gnu_parallel::count`	`parallel/algorithm`
`std::count_if`	`algorithm`	`__gnu_parallel::count_if`	`parallel/algorithm`
`std::equal`	`algorithm`	`__gnu_parallel::equal`	`parallel/algorithm`
`std::find`	`algorithm`	`__gnu_parallel::find`	`parallel/algorithm`
`std::find_if`	`algorithm`	`__gnu_parallel::find_if`	`parallel/algorithm`
`std::find_first_of`	`algorithm`	`__gnu_parallel::find_first_of`	`parallel/algorithm`
`std::for_each`	`algorithm`	`__gnu_parallel::for_each`	`parallel/algorithm`
`std::generate`	`algorithm`	`__gnu_parallel::generate`	`parallel/algorithm`
`std::generate_n`	`algorithm`	`__gnu_parallel::generate_n`	`parallel/algorithm`
`std::lexicographical_compare`	`algorithm`	`__gnu_parallel::lexicographical_compare`	`parallel/algorithm`
`std::mismatch`	`algorithm`	`__gnu_parallel::mismatch`	`parallel/algorithm`
`std::search`	`algorithm`	`__gnu_parallel::search`	`parallel/algorithm`
`std::search_n`	`algorithm`	`__gnu_parallel::search_n`	`parallel/algorithm`
`std::transform`	`algorithm`	`__gnu_parallel::transform`	`parallel/algorithm`
`std::replace`	`algorithm`	`__gnu_parallel::replace`	`parallel/algorithm`
`std::replace_if`	`algorithm`	`__gnu_parallel::replace_if`	`parallel/algorithm`
`std::max_element`	`algorithm`	`__gnu_parallel::max_element`	`parallel/algorithm`
`std::merge`	`algorithm`	`__gnu_parallel::merge`	`parallel/algorithm`
`std::min_element`	`algorithm`	`__gnu_parallel::min_element`	`parallel/algorithm`
`std::nth_element`	`algorithm`	`__gnu_parallel::nth_element`	`parallel/algorithm`
`std::partial_sort`	`algorithm`	`__gnu_parallel::partial_sort`	`parallel/algorithm`
`std::partition`	`algorithm`	`__gnu_parallel::partition`	`parallel/algorithm`
`std::random_shuffle`	`algorithm`	`__gnu_parallel::random_shuffle`	`parallel/algorithm`
`std::set_union`	`algorithm`	`__gnu_parallel::set_union`	`parallel/algorithm`
`std::set_intersection`	`algorithm`	`__gnu_parallel::set_intersection`	`parallel/algorithm`
`std::set_symmetric_difference`	`algorithm`	`__gnu_parallel::set_symmetric_difference`	`parallel/algorithm`
`std::set_difference`	`algorithm`	`__gnu_parallel::set_difference`	`parallel/algorithm`
`std::sort`	`algorithm`	`__gnu_parallel::sort`	`parallel/algorithm`
`std::stable_sort`	`algorithm`	`__gnu_parallel::stable_sort`	`parallel/algorithm`
`std::unique_copy`	`algorithm`	`__gnu_parallel::unique_copy`	`parallel/algorithm`

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