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b9a2658a3e
This patch implements the forwarding to frozen C++03 headers as discussed in https://discourse.llvm.org/t/rfc-freezing-c-03-headers-in-libc. In the RFC, we initially proposed selecting the right headers from the Clang driver, however consensus seemed to steer towards handling this in the library itself. This patch implements that direction. At a high level, the changes basically amount to making each public header look like this: ``` // inside <vector> #ifdef _LIBCPP_CXX03_LANG # include <__cxx03/vector> #else // normal <vector> content #endif ``` In most cases, public headers are simple umbrella headers so there isn't much code in the #else branch. In other cases, the #else branch contains the actual implementation of the header.
136 lines
3.9 KiB
C++
136 lines
3.9 KiB
C++
// -*- C++ -*-
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//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP_LATCH
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#define _LIBCPP_LATCH
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/*
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latch synopsis
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namespace std
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{
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class latch // since C++20
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{
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public:
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static constexpr ptrdiff_t max() noexcept;
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constexpr explicit latch(ptrdiff_t __expected);
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~latch();
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latch(const latch&) = delete;
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latch& operator=(const latch&) = delete;
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void count_down(ptrdiff_t __update = 1);
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bool try_wait() const noexcept;
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void wait() const;
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void arrive_and_wait(ptrdiff_t __update = 1);
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private:
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ptrdiff_t __counter; // exposition only
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};
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}
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*/
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#if __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
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# include <__cxx03/latch>
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#else
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# include <__config>
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# if _LIBCPP_HAS_THREADS
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# include <__assert>
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# include <__atomic/atomic.h>
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# include <__atomic/atomic_sync.h>
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# include <__atomic/memory_order.h>
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# include <__cstddef/ptrdiff_t.h>
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# include <limits>
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# include <version>
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# if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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# endif
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_LIBCPP_PUSH_MACROS
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# include <__undef_macros>
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# if _LIBCPP_STD_VER >= 20
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_LIBCPP_BEGIN_NAMESPACE_STD
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class latch {
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atomic<ptrdiff_t> __a_;
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public:
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static _LIBCPP_HIDE_FROM_ABI constexpr ptrdiff_t max() noexcept { return numeric_limits<ptrdiff_t>::max(); }
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inline _LIBCPP_HIDE_FROM_ABI constexpr explicit latch(ptrdiff_t __expected) : __a_(__expected) {
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_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
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__expected >= 0,
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"latch::latch(ptrdiff_t): latch cannot be "
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"initialized with a negative value");
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_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
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__expected <= max(),
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"latch::latch(ptrdiff_t): latch cannot be "
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"initialized with a value greater than max()");
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}
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_LIBCPP_HIDE_FROM_ABI ~latch() = default;
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latch(const latch&) = delete;
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latch& operator=(const latch&) = delete;
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void count_down(ptrdiff_t __update = 1) {
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_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "latch::count_down called with a negative value");
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auto const __old = __a_.fetch_sub(__update, memory_order_release);
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_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(
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__update <= __old,
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"latch::count_down called with a value greater "
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"than the internal counter");
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if (__old == __update)
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__a_.notify_all();
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}
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inline _LIBCPP_HIDE_FROM_ABI bool try_wait() const noexcept {
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auto __value = __a_.load(memory_order_acquire);
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return try_wait_impl(__value);
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}
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void wait() const {
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std::__atomic_wait_unless(__a_, memory_order_acquire, [this](ptrdiff_t& __value) -> bool {
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return try_wait_impl(__value);
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});
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}
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inline _LIBCPP_AVAILABILITY_SYNC _LIBCPP_HIDE_FROM_ABI void arrive_and_wait(ptrdiff_t __update = 1) {
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_LIBCPP_ASSERT_ARGUMENT_WITHIN_DOMAIN(__update >= 0, "latch::arrive_and_wait called with a negative value");
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// other preconditions on __update are checked in count_down()
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count_down(__update);
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wait();
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}
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private:
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_LIBCPP_HIDE_FROM_ABI bool try_wait_impl(ptrdiff_t& __value) const noexcept { return __value == 0; }
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};
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_LIBCPP_END_NAMESPACE_STD
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# endif // _LIBCPP_STD_VER >= 20
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_LIBCPP_POP_MACROS
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# endif // _LIBCPP_HAS_THREADS
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# if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
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# include <atomic>
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# include <cstddef>
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# endif
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#endif // __cplusplus < 201103L && defined(_LIBCPP_USE_FROZEN_CXX03_HEADERS)
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#endif // _LIBCPP_LATCH
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