1a5af34e6f
Locale objects use atomic reference counting, which may be very expensive in parallel applications. The classic locale is used by default by all streams and can be very contended. But it's never destroyed, so the reference counting is also completely pointless on the classic locale. Currently ~70% of time in the parallel stringstream benchmarks is spent in locale ctor/dtor. And the execution radically slows down with more threads. Avoid reference counting on the classic locale. With this change parallel benchmarks start to scale with threads. This is a re-application off8afc53d64(aka PR #72112) which was reverted in4e0c48b907because it broke the sanitizer builds due to an initialization order fiasco. This issue has now been fixed by ensuring that the locale is constinit'ed. Co-authored-by: Dmitry Vyukov <dvyukov@google.com>
64 lines
2.0 KiB
C++
64 lines
2.0 KiB
C++
//===----------------------------------------------------------------------===//
|
|
//
|
|
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
|
|
// See https://llvm.org/LICENSE.txt for license information.
|
|
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
|
|
//
|
|
//===----------------------------------------------------------------------===//
|
|
|
|
#ifndef _LIBCPP___UTILITY_NO_DESTROY_H
|
|
#define _LIBCPP___UTILITY_NO_DESTROY_H
|
|
|
|
#include <__config>
|
|
#include <__type_traits/is_constant_evaluated.h>
|
|
#include <__utility/forward.h>
|
|
|
|
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
|
|
# pragma GCC system_header
|
|
#endif
|
|
|
|
_LIBCPP_BEGIN_NAMESPACE_STD
|
|
|
|
struct __uninitialized_tag {};
|
|
|
|
// This class stores an object of type _Tp but never destroys it.
|
|
//
|
|
// This is akin to using __attribute__((no_destroy)), except that it is possible
|
|
// to control the lifetime of the object with more flexibility by deciding e.g.
|
|
// whether to initialize the object at construction or to defer to a later
|
|
// initialization using __emplace.
|
|
template <class _Tp>
|
|
struct __no_destroy {
|
|
_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(__uninitialized_tag) : __dummy_() {
|
|
if (__libcpp_is_constant_evaluated()) {
|
|
__dummy_ = char();
|
|
}
|
|
}
|
|
_LIBCPP_HIDE_FROM_ABI ~__no_destroy() {
|
|
// nothing
|
|
}
|
|
|
|
template <class... _Args>
|
|
_LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI explicit __no_destroy(_Args&&... __args)
|
|
: __obj_(std::forward<_Args>(__args)...) {}
|
|
|
|
template <class... _Args>
|
|
_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __emplace(_Args&&... __args) {
|
|
new (&__obj_) _Tp(std::forward<_Args>(__args)...);
|
|
return __obj_;
|
|
}
|
|
|
|
_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp& __get() { return __obj_; }
|
|
_LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI _Tp const& __get() const { return __obj_; }
|
|
|
|
private:
|
|
union {
|
|
_Tp __obj_;
|
|
char __dummy_; // so we can initialize a member even with __uninitialized_tag for constexpr-friendliness
|
|
};
|
|
};
|
|
|
|
_LIBCPP_END_NAMESPACE_STD
|
|
|
|
#endif // _LIBCPP___UTILITY_NO_DESTROY_H
|