libcxx/include/__stop_token/intrusive_list_view.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___STOP_TOKEN_INTRUSIVE_LIST_VIEW_H
  11 #define _LIBCPP___STOP_TOKEN_INTRUSIVE_LIST_VIEW_H
  12
  13 #include <__assert>
  14 #include <__config>
  15
  16 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  17 #  pragma GCC system_header
  18 #endif
  19
  20 _LIBCPP_BEGIN_NAMESPACE_STD
  21
  22 #if _LIBCPP_STD_VER >= 20
  23
  24 template <class _Derived>
  25 struct __intrusive_node_base {
  26   _Derived* __next_ = nullptr;
  27   _Derived* __prev_ = nullptr;
  28 };
  29
  30 // This class is a view of underlying double-linked list.
  31 // It does not own the nodes. It provides user-friendly
  32 // operations on the linked list.
  33 template <class _Node>
  34 struct __intrusive_list_view {
  35   _LIBCPP_HIDE_FROM_ABI __intrusive_list_view()                                        = default;
  36   _LIBCPP_HIDE_FROM_ABI __intrusive_list_view(__intrusive_list_view const&)            = default;
  37   _LIBCPP_HIDE_FROM_ABI __intrusive_list_view(__intrusive_list_view&&)                 = default;
  38   _LIBCPP_HIDE_FROM_ABI __intrusive_list_view& operator=(__intrusive_list_view const&) = default;
  39   _LIBCPP_HIDE_FROM_ABI __intrusive_list_view& operator=(__intrusive_list_view&&)      = default;
  40   _LIBCPP_HIDE_FROM_ABI ~__intrusive_list_view()                                       = default;
  41
  42   _LIBCPP_HIDE_FROM_ABI bool __empty() const noexcept { return __head_ == nullptr; }
  43
  44   _LIBCPP_HIDE_FROM_ABI void __push_front(_Node* __node) noexcept {
  45     __node->__next_ = __head_;
  46     if (__head_) {
  47       __head_->__prev_ = __node;
  48     }
  49     __head_ = __node;
  50   }
  51
  52   _LIBCPP_HIDE_FROM_ABI _Node* __pop_front() noexcept {
  53     _Node* __front = __head_;
  54     __head_        = __head_->__next_;
  55     if (__head_) {
  56       __head_->__prev_ = nullptr;
  57     }
  58     // OK not to set __front->__next_ = nullptr as __front is not part of the list anymore
  59     return __front;
  60   }
  61
  62   _LIBCPP_HIDE_FROM_ABI void __remove(_Node* __node) noexcept {
  63     if (__node->__prev_) {
  64       // prev exists, set its next to our next to skip __node
  65       __node->__prev_->__next_ = __node->__next_;
  66       if (__node->__next_) {
  67         __node->__next_->__prev_ = __node->__prev_;
  68       }
  69     } else {
  70       _LIBCPP_ASSERT_INTERNAL(__node == __head_, "Node to be removed has no prev node, so it has to be the head");
  71       __pop_front();
  72     }
  73   }
  74
  75   _LIBCPP_HIDE_FROM_ABI bool __is_head(_Node* __node) noexcept { return __node == __head_; }
  76
  77 private:
  78   _Node* __head_ = nullptr;
  79 };
  80
  81 #endif // _LIBCPP_STD_VER >= 20
  82
  83 _LIBCPP_END_NAMESPACE_STD
  84
  85 #endif // _LIBCPP___STOP_TOKEN_INTRUSIVE_LIST_VIEW_H