2 * Copyright 2016-present 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.
21 /* Stand-in for C++17 std::pmr::memory_resource */
22 #include <folly/experimental/hazptr/memory_resource.h>
27 /** hazptr_rec: Private class that contains hazard pointers. */
30 /** hazptr_obj: Private class for objects protected by hazard pointers. */
33 /** hazptr_obj_base: Base template for objects protected by hazard pointers. */
34 template <typename T, typename Deleter>
35 class hazptr_obj_base;
37 /** hazptr_obj_base_refcounted:
38 * Base template for reference counted objects protected by hazard pointers.
40 template <typename T, typename Deleter>
41 class hazptr_obj_base_refcounted;
43 /** hazptr_local: Optimized template for bulk construction and destruction of
48 /** hazptr_local: Optimized template for locally-used hazard pointers */
52 /** hazptr_domain: Class of hazard pointer domains. Each domain manages a set
53 * of hazard pointers and a set of retired objects. */
56 constexpr explicit hazptr_domain(
57 memory_resource* = get_default_resource()) noexcept;
60 hazptr_domain(const hazptr_domain&) = delete;
61 hazptr_domain(hazptr_domain&&) = delete;
62 hazptr_domain& operator=(const hazptr_domain&) = delete;
63 hazptr_domain& operator=(hazptr_domain&&) = delete;
65 /** Free-function retire. May allocate memory */
66 template <typename T, typename D = std::default_delete<T>>
67 void retire(T* obj, D reclaim = {});
70 friend class hazptr_obj_batch;
71 friend class hazptr_holder;
72 template <typename, typename>
73 friend class hazptr_obj_base;
74 template <typename, typename>
75 friend class hazptr_obj_base_refcounted;
76 friend struct hazptr_priv;
79 std::atomic<hazptr_rec*> hazptrs_ = {nullptr};
80 std::atomic<hazptr_obj*> retired_ = {nullptr};
81 std::atomic<int> hcount_ = {0};
82 std::atomic<int> rcount_ = {0};
84 void objRetire(hazptr_obj*);
85 hazptr_rec* hazptrAcquire();
86 void hazptrRelease(hazptr_rec*) noexcept;
87 int pushRetired(hazptr_obj* head, hazptr_obj* tail, int count);
88 bool reachedThreshold(int rcount);
89 void tryBulkReclaim();
93 /** Get the default hazptr_domain */
94 hazptr_domain& default_hazptr_domain();
96 extern hazptr_domain default_domain_;
98 /** Free-function retire, that operates on the default domain */
99 template <typename T, typename D = std::default_delete<T>>
100 void hazptr_retire(T* obj, D reclaim = {});
102 /** Definition of hazptr_obj */
104 friend class hazptr_obj_batch;
105 friend class hazptr_domain;
106 template <typename, typename>
107 friend class hazptr_obj_base;
108 template <typename, typename>
109 friend class hazptr_obj_base_refcounted;
110 friend struct hazptr_priv;
112 void (*reclaim_)(hazptr_obj*);
113 hazptr_obj* next_{nullptr}; // nullptr for debugging
115 const void* getObjPtr() const;
118 /** Definition of hazptr_obj_base */
119 template <typename T, typename D = std::default_delete<T>>
120 class hazptr_obj_base : public hazptr_obj {
122 /* Retire a removed object and pass the responsibility for
123 * reclaiming it to the hazptr library */
124 void retire(hazptr_domain& domain = default_hazptr_domain(), D reclaim = {});
130 /** Definition of hazptr_recounted_obj_base */
131 template <typename T, typename D = std::default_delete<T>>
132 class hazptr_obj_base_refcounted : public hazptr_obj {
133 friend class hazptr_obj_batch;
136 /* Retire a removed object and pass the responsibility for
137 * reclaiming it to the hazptr library */
138 void retire(hazptr_domain& domain = default_hazptr_domain(), D reclaim = {});
140 /* aquire_ref() increments the reference count
142 * acquire_ref_safe() is the same as acquire_ref() except that in
143 * addition the caller guarantees that the call is made in a
144 * thread-safe context, e.g., the object is not yet shared. This is
145 * just an optimization to save an atomic operation.
147 * release_ref() decrements the reference count and returns true if
148 * the object is safe to reclaim.
151 void acquire_ref_safe();
155 void preRetire(D deleter);
157 std::atomic<uint32_t> refcount_{0};
161 /** hazptr_holder: Class for automatic acquisition and release of
162 * hazard pointers, and interface for hazard pointer operations. */
163 class hazptr_holder {
165 friend class hazptr_array;
167 friend class hazptr_local;
170 /* Constructor automatically acquires a hazard pointer. */
171 explicit hazptr_holder(hazptr_domain& domain = default_hazptr_domain());
172 /* Construct an empty hazptr_holder. */
173 // Note: This diverges from the proposal in P0233R4
174 explicit hazptr_holder(std::nullptr_t) noexcept;
176 /* Destructor automatically clears and releases the owned hazard pointer. */
179 hazptr_holder(const hazptr_holder&) = delete;
180 hazptr_holder& operator=(const hazptr_holder&) = delete;
181 // Note: This diverges from the proposal in P0233R4 which disallows
182 // move constructor and assignment operator.
183 hazptr_holder(hazptr_holder&&) noexcept;
184 hazptr_holder& operator=(hazptr_holder&&) noexcept;
186 /** Hazard pointer operations */
187 /* Returns a protected pointer from the source */
188 template <typename T>
189 T* get_protected(const std::atomic<T*>& src) noexcept;
190 /* Returns a protected pointer from the source, filtering
191 the protected pointer through function Func. Useful for
192 stealing bits of the pointer word */
193 template <typename T, typename Func>
194 T* get_protected(const std::atomic<T*>& src, Func f) noexcept;
195 /* Return true if successful in protecting ptr if src == ptr after
196 * setting the hazard pointer. Otherwise sets ptr to src. */
197 template <typename T>
198 bool try_protect(T*& ptr, const std::atomic<T*>& src) noexcept;
199 /* Return true if successful in protecting ptr if src == ptr after
200 * setting the hazard pointer, filtering the pointer through Func.
201 * Otherwise sets ptr to src. */
202 template <typename T, typename Func>
203 bool try_protect(T*& ptr, const std::atomic<T*>& src, Func f) noexcept;
204 /* Set the hazard pointer to ptr */
205 template <typename T>
206 void reset(const T* ptr) noexcept;
207 /* Set the hazard pointer to nullptr */
208 void reset(std::nullptr_t = nullptr) noexcept;
210 /* Swap ownership of hazard pointers between hazptr_holder-s. */
211 /* Note: The owned hazard pointers remain unmodified during the swap
212 * and continue to protect the respective objects that they were
213 * protecting before the swap, if any. */
214 void swap(hazptr_holder&) noexcept;
217 hazptr_domain* domain_;
221 void swap(hazptr_holder&, hazptr_holder&) noexcept;
223 using aligned_hazptr_holder = typename std::
224 aligned_storage<sizeof(hazptr_holder), alignof(hazptr_holder)>::type;
227 * hazptr_array: Optimized for bulk construction and destruction of
230 * WARNING: Do not move from or to individual hazptr_holder-s.
231 * Only move the whole hazptr_array.
233 template <size_t M = 1>
235 static_assert(M > 0, "M must be a positive integer.");
239 explicit hazptr_array(std::nullptr_t) noexcept;
241 hazptr_array(const hazptr_array&) = delete;
242 hazptr_array& operator=(const hazptr_array&) = delete;
243 hazptr_array(hazptr_array&& other) noexcept;
244 hazptr_array& operator=(hazptr_array&& other) noexcept;
248 hazptr_holder& operator[](size_t i) noexcept;
251 aligned_hazptr_holder raw_[M];
256 * hazptr_local: Optimized for construction and destruction of
257 * one or more hazptr_holder-s with local scope.
259 * WARNING 1: Do not move from or to individual hazptr_holder-s.
261 * WARNING 2: There can only be one hazptr_local active for the same
262 * thread at any time. This is not tracked and checked by the
263 * implementation because it would negate the performance gains of
266 template <size_t M = 1>
268 static_assert(M > 0, "M must be a positive integer.");
272 hazptr_local(const hazptr_local&) = delete;
273 hazptr_local& operator=(const hazptr_local&) = delete;
274 hazptr_local(hazptr_local&&) = delete;
275 hazptr_local& operator=(hazptr_local&&) = delete;
279 hazptr_holder& operator[](size_t i) noexcept;
282 aligned_hazptr_holder raw_[M];
283 bool need_destruct_{false};
286 } // namespace hazptr
289 #include "hazptr-impl.h"