The PSTL (or Parallel STL) project is quite complex in its current form and does not provide everything that libc++
requires, for example
_LIBCPP_HIDE_FROM_ABI or similar annotations and including granularized headers. Furthermore,
the PSTL provides various layers of indirection that make sense in a generic implementation of the parallel algorithms,
but are unnecessarily complex in the context of a single standard library implementation. Because of these drawbacks, we
decided to adopt a modified PSTL in libc++. Specifically, the goals of the modified PSTL are
<__pstl_algorithm>and similar glue headers – instead, the implementation files are included directly in
<pstl/internal/algorithm_fwd.h>headers and friends – these contain the implementation and forward declarations for internal functions respectively. The implementation lives inside
<__algorithm/pstl_any_of.h>and friends, and the forward declarations are not needed inside libc++.
<pstl/internal/glue_algorithm_impl.h>headers and friends – these contain the public API. It lives inside
<__algorithm/pstl_any_of.h>and friends instead.
The headers implementing backends are kept with as few changes as possible to make it easier to keep the backends in sync with the backends from the original PSTL.
The configuration headers
pstl_config.hare removed, and any required configuration is done inside
libc++-style tests for the public PSTL API