Keywords: C++ , library , parallel

Using
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## Using

### Using Parallel Mode

To use the libstdc++ parallel mode, compile your application with the compiler flag `-D_GLIBCXX_PARALLEL -fopenmp`. This will link in `libgomp`, the GNU OpenMP implementation, whose presence is mandatory. In addition, hardware capable of atomic operations is mandatory. Actually activating these atomic operations may require explicit compiler flags on some targets (like sparc and x86), such as `-march=i686`, `-march=native` or `-mcpu=v9`.

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. The following table provides the names and headers of the parallel algorithms:

Table 31.1. 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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