2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
22 #include <type_traits>
24 /* Stand-in for C++17 std::pmr::memory_resource */
25 #include <folly/experimental/hazptr/memory_resource.h>
30 /** hazptr_rec: Private class that contains hazard pointers. */
33 /** hazptr_obj: Private class for objects protected by hazard pointers. */
36 /** hazptr_obj_base: Base template for objects protected by hazard pointers. */
37 template <typename T, typename Deleter>
38 class hazptr_obj_base;
40 /** hazptr_domain: Class of hazard pointer domains. Each domain manages a set
41 * of hazard pointers and a set of retired objects. */
44 constexpr explicit hazptr_domain(
45 memory_resource* = get_default_resource()) noexcept;
48 hazptr_domain(const hazptr_domain&) = delete;
49 hazptr_domain(hazptr_domain&&) = delete;
50 hazptr_domain& operator=(const hazptr_domain&) = delete;
51 hazptr_domain& operator=(hazptr_domain&&) = delete;
54 template <typename, typename>
55 friend class hazptr_obj_base;
56 friend class hazptr_holder;
59 std::atomic<hazptr_rec*> hazptrs_ = {nullptr};
60 std::atomic<hazptr_obj*> retired_ = {nullptr};
61 std::atomic<int> hcount_ = {0};
62 std::atomic<int> rcount_ = {0};
64 void objRetire(hazptr_obj*);
65 hazptr_rec* hazptrAcquire();
66 void hazptrRelease(hazptr_rec*) noexcept;
67 int pushRetired(hazptr_obj* head, hazptr_obj* tail, int count);
68 void tryBulkReclaim();
72 /** Get the default hazptr_domain */
73 hazptr_domain& default_hazptr_domain();
75 /** Definition of hazptr_obj */
77 friend class hazptr_domain;
78 template <typename, typename>
79 friend class hazptr_obj_base;
81 void (*reclaim_)(hazptr_obj*);
83 const void* getObjPtr() const;
86 /** Definition of hazptr_obj_base */
87 template <typename T, typename Deleter = std::default_delete<T>>
88 class hazptr_obj_base : public hazptr_obj {
90 /* Retire a removed object and pass the responsibility for
91 * reclaiming it to the hazptr library */
93 hazptr_domain& domain = default_hazptr_domain(),
94 Deleter reclaim = {});
100 /** hazptr_holder: Class for automatic acquisition and release of
101 * hazard pointers, and interface for hazard pointer operations. */
102 class hazptr_holder {
104 /* Constructor automatically acquires a hazard pointer. */
105 explicit hazptr_holder(hazptr_domain& domain = default_hazptr_domain());
106 /* Destructor automatically clears and releases the owned hazard pointer. */
109 /* Copy and move constructors and assignment operators are
110 * disallowed because:
111 * - Each hazptr_holder owns exactly one hazard pointer at any time.
112 * - Each hazard pointer may have up to one owner at any time. */
113 hazptr_holder(const hazptr_holder&) = delete;
114 hazptr_holder(hazptr_holder&&) = delete;
115 hazptr_holder& operator=(const hazptr_holder&) = delete;
116 hazptr_holder& operator=(hazptr_holder&&) = delete;
118 /** Hazard pointer operations */
119 /* Returns a protected pointer from the source */
120 template <typename T>
121 T* get_protected(const std::atomic<T*>& src) noexcept;
122 /* Return true if successful in protecting ptr if src == ptr after
123 * setting the hazard pointer. Otherwise sets ptr to src. */
124 template <typename T>
125 bool try_protect(T*& ptr, const std::atomic<T*>& src) noexcept;
126 /* Set the hazard pointer to ptr */
127 template <typename T>
128 void reset(const T* ptr) noexcept;
129 /* Set the hazard pointer to nullptr */
130 void reset(std::nullptr_t = nullptr) noexcept;
132 /* Swap ownership of hazard pointers between hazptr_holder-s. */
133 /* Note: The owned hazard pointers remain unmodified during the swap
134 * and continue to protect the respective objects that they were
135 * protecting before the swap, if any. */
136 void swap(hazptr_holder&) noexcept;
139 hazptr_domain* domain_;
143 void swap(hazptr_holder&, hazptr_holder&) noexcept;
145 } // namespace hazptr
148 #include "hazptr-impl.h"