| Line | Branch | Exec | Source |
|---|---|---|---|
| 1 | // | ||
| 2 | // Copyright (c) 2025 Vinnie Falco (vinnie.falco@gmail.com) | ||
| 3 | // | ||
| 4 | // Distributed under the Boost Software License, Version 1.0. (See accompanying | ||
| 5 | // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) | ||
| 6 | // | ||
| 7 | // Official repository: https://github.com/cppalliance/capy | ||
| 8 | // | ||
| 9 | |||
| 10 | #ifndef BOOST_CAPY_THREAD_LOCAL_PTR_HPP | ||
| 11 | #define BOOST_CAPY_THREAD_LOCAL_PTR_HPP | ||
| 12 | |||
| 13 | #include <boost/capy/detail/config.hpp> | ||
| 14 | |||
| 15 | #include <type_traits> | ||
| 16 | |||
| 17 | namespace boost { | ||
| 18 | namespace capy { | ||
| 19 | namespace detail { | ||
| 20 | |||
| 21 | /** A thread-local pointer. | ||
| 22 | |||
| 23 | This class provides thread-local storage for a pointer to T. | ||
| 24 | Each thread has its own independent pointer value, initially | ||
| 25 | nullptr. The user is responsible for managing the lifetime | ||
| 26 | of the pointed-to objects. | ||
| 27 | |||
| 28 | The storage is static per type T. All instances of | ||
| 29 | `thread_local_ptr<T>` share the same underlying slot. | ||
| 30 | |||
| 31 | The implementation uses the most efficient available mechanism: | ||
| 32 | 1. Compiler keyword (__declspec(thread) or __thread) - enforces POD | ||
| 33 | 2. C++11 thread_local (fallback) | ||
| 34 | |||
| 35 | @tparam T The pointed-to type. | ||
| 36 | |||
| 37 | @par Declaration | ||
| 38 | |||
| 39 | Typically declared at namespace or class scope. The object | ||
| 40 | is stateless, so local variables work but are redundant. | ||
| 41 | |||
| 42 | @code | ||
| 43 | // Recommended: namespace scope | ||
| 44 | namespace { | ||
| 45 | thread_local_ptr<session> current_session; | ||
| 46 | } | ||
| 47 | |||
| 48 | // Also works: static class member | ||
| 49 | class server { | ||
| 50 | static thread_local_ptr<request> current_request_; | ||
| 51 | }; | ||
| 52 | |||
| 53 | // Works but unusual: local variable (still accesses static storage) | ||
| 54 | void foo() { | ||
| 55 | thread_local_ptr<context> ctx; // same slot on every call | ||
| 56 | ctx = new context(); | ||
| 57 | } | ||
| 58 | @endcode | ||
| 59 | |||
| 60 | @note The user is responsible for deleting pointed-to objects | ||
| 61 | before threads exit to avoid memory leaks. | ||
| 62 | */ | ||
| 63 | template<class T> | ||
| 64 | class thread_local_ptr; | ||
| 65 | |||
| 66 | //------------------------------------------------------------------------------ | ||
| 67 | |||
| 68 | #if defined(BOOST_CAPY_TLS_KEYWORD) | ||
| 69 | |||
| 70 | // Use compiler-specific keyword (__declspec(thread) or __thread) | ||
| 71 | // Most efficient: static linkage, no dynamic init, enforces POD | ||
| 72 | |||
| 73 | template<class T> | ||
| 74 | class thread_local_ptr | ||
| 75 | { | ||
| 76 | static BOOST_CAPY_TLS_KEYWORD T* ptr_; | ||
| 77 | |||
| 78 | public: | ||
| 79 | thread_local_ptr() = default; | ||
| 80 | ~thread_local_ptr() = default; | ||
| 81 | |||
| 82 | thread_local_ptr(thread_local_ptr const&) = delete; | ||
| 83 | thread_local_ptr& operator=(thread_local_ptr const&) = delete; | ||
| 84 | |||
| 85 | /** Return the pointer for this thread. | ||
| 86 | |||
| 87 | @return The stored pointer, or nullptr if not set. | ||
| 88 | */ | ||
| 89 | T* | ||
| 90 | 26 | get() const noexcept | |
| 91 | { | ||
| 92 | 26 | return ptr_; | |
| 93 | } | ||
| 94 | |||
| 95 | /** Set the pointer for this thread. | ||
| 96 | |||
| 97 | @param p The pointer to store. The user manages its lifetime. | ||
| 98 | */ | ||
| 99 | void | ||
| 100 | 2 | set(T* p) noexcept | |
| 101 | { | ||
| 102 | 2 | ptr_ = p; | |
| 103 | 2 | } | |
| 104 | |||
| 105 | /** Dereference the stored pointer. | ||
| 106 | |||
| 107 | @pre get() != nullptr | ||
| 108 | */ | ||
| 109 | T& | ||
| 110 | 2 | operator*() const noexcept | |
| 111 | { | ||
| 112 | 2 | return *ptr_; | |
| 113 | } | ||
| 114 | |||
| 115 | /** Member access through the stored pointer. | ||
| 116 | |||
| 117 | @pre get() != nullptr | ||
| 118 | */ | ||
| 119 | T* | ||
| 120 | 5 | operator->() const noexcept | |
| 121 | requires std::is_class_v<T> | ||
| 122 | { | ||
| 123 | 5 | return ptr_; | |
| 124 | } | ||
| 125 | |||
| 126 | /** Assign a pointer value. | ||
| 127 | |||
| 128 | @param p The pointer to store. | ||
| 129 | @return The stored pointer. | ||
| 130 | */ | ||
| 131 | T* | ||
| 132 | 9 | operator=(T* p) noexcept | |
| 133 | { | ||
| 134 | 9 | ptr_ = p; | |
| 135 | 9 | return p; | |
| 136 | } | ||
| 137 | }; | ||
| 138 | |||
| 139 | template<class T> | ||
| 140 | BOOST_CAPY_TLS_KEYWORD T* thread_local_ptr<T>::ptr_ = nullptr; | ||
| 141 | |||
| 142 | //------------------------------------------------------------------------------ | ||
| 143 | |||
| 144 | #else | ||
| 145 | |||
| 146 | // Use C++11 thread_local keyword (fallback) | ||
| 147 | |||
| 148 | template<class T> | ||
| 149 | class thread_local_ptr | ||
| 150 | { | ||
| 151 | static thread_local T* ptr_; | ||
| 152 | |||
| 153 | public: | ||
| 154 | thread_local_ptr() = default; | ||
| 155 | ~thread_local_ptr() = default; | ||
| 156 | |||
| 157 | thread_local_ptr(thread_local_ptr const&) = delete; | ||
| 158 | thread_local_ptr& operator=(thread_local_ptr const&) = delete; | ||
| 159 | |||
| 160 | T* | ||
| 161 | get() const noexcept | ||
| 162 | { | ||
| 163 | return ptr_; | ||
| 164 | } | ||
| 165 | |||
| 166 | void | ||
| 167 | set(T* p) noexcept | ||
| 168 | { | ||
| 169 | ptr_ = p; | ||
| 170 | } | ||
| 171 | |||
| 172 | T& | ||
| 173 | operator*() const noexcept | ||
| 174 | { | ||
| 175 | return *ptr_; | ||
| 176 | } | ||
| 177 | |||
| 178 | T* | ||
| 179 | operator->() const noexcept | ||
| 180 | requires std::is_class_v<T> | ||
| 181 | { | ||
| 182 | return ptr_; | ||
| 183 | } | ||
| 184 | |||
| 185 | T* | ||
| 186 | operator=(T* p) noexcept | ||
| 187 | { | ||
| 188 | ptr_ = p; | ||
| 189 | return p; | ||
| 190 | } | ||
| 191 | }; | ||
| 192 | |||
| 193 | template<class T> | ||
| 194 | thread_local T* thread_local_ptr<T>::ptr_ = nullptr; | ||
| 195 | |||
| 196 | #endif | ||
| 197 | |||
| 198 | } // namespace detail | ||
| 199 | } // namespace capy | ||
| 200 | } // namespace boost | ||
| 201 | |||
| 202 | #endif | ||
| 203 |