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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9// For information see https://libcxx.llvm.org/DesignDocs/TimeZone.html10 11#ifndef _LIBCPP_SRC_INCLUDE_TZDB_TZDB_LIST_PRIVATE_H12#define _LIBCPP_SRC_INCLUDE_TZDB_TZDB_LIST_PRIVATE_H13 14#include <__mutex/unique_lock.h>15#include <forward_list>16 17// When threads are not available the locking is not required.18// When threads are available, we use std::mutex over std::shared_mutex19// due to the increased overhead of std::shared_mutex.20// See shared_mutex_vs_mutex.bench.cpp21#if _LIBCPP_HAS_THREADS22# include <mutex>23#endif24 25#include "types_private.h"26#include "tzdb_private.h"27 28_LIBCPP_BEGIN_NAMESPACE_STD29 30namespace chrono {31 32//===----------------------------------------------------------------------===//33// Private API34//===----------------------------------------------------------------------===//35 36// The tzdb_list stores a list of "tzdb" entries.37//38// The public tzdb database does not store the RULE entries of the IANA39// database. These entries are considered an implementation detail. Since most40// of the tzdb_list interface is exposed as "a list of tzdb entries" it's not41// possible to use a helper struct that stores a tzdb and the RULE database.42// Instead this class stores these in parallel forward lists.43//44// Since the nodes of a forward_list are stable it's possible to store pointers45// and references to these nodes.46class tzdb_list::__impl {47public:48 __impl() { __load_no_lock(); }49 50 [[nodiscard]] const tzdb& __load() {51#if _LIBCPP_HAS_THREADS52 unique_lock __lock{__mutex_};53#endif54 __load_no_lock();55 return __tzdb_.front();56 }57 58 using const_iterator = tzdb_list::const_iterator;59 60 const tzdb& __front() const noexcept {61#if _LIBCPP_HAS_THREADS62 unique_lock __lock{__mutex_};63#endif64 return __tzdb_.front();65 }66 67 const_iterator __erase_after(const_iterator __p) {68#if _LIBCPP_HAS_THREADS69 unique_lock __lock{__mutex_};70#endif71 72 __rules_.erase_after(std::next(__rules_.cbegin(), std::distance(__tzdb_.cbegin(), __p)));73 return __tzdb_.erase_after(__p);74 }75 76 const_iterator __begin() const noexcept {77#if _LIBCPP_HAS_THREADS78 unique_lock __lock{__mutex_};79#endif80 return __tzdb_.begin();81 }82 const_iterator __end() const noexcept {83 // forward_list<T>::end does not access the list, so no need to take a lock.84 return __tzdb_.end();85 }86 87private:88 // Loads the tzdbs89 // pre: The caller ensures the locking, if needed, is done.90 void __load_no_lock() { chrono::__init_tzdb(__tzdb_.emplace_front(), __rules_.emplace_front()); }91 92#if _LIBCPP_HAS_THREADS93 mutable mutex __mutex_;94#endif95 forward_list<tzdb> __tzdb_;96 97 forward_list<__tz::__rules_storage_type> __rules_;98};99 100} // namespace chrono101 102_LIBCPP_END_NAMESPACE_STD103 104#endif // _LIBCPP_SRC_INCLUDE_TZDB_TZDB_LIST_PRIVATE_H105