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.
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_holder;
71 template <typename, typename>
72 friend class hazptr_obj_base;
73 template <typename, typename>
74 friend class hazptr_obj_base_refcounted;
75 friend struct hazptr_priv;
78 std::atomic<hazptr_rec*> hazptrs_ = {nullptr};
79 std::atomic<hazptr_obj*> retired_ = {nullptr};
80 std::atomic<int> hcount_ = {0};
81 std::atomic<int> rcount_ = {0};
83 void objRetire(hazptr_obj*);
84 hazptr_rec* hazptrAcquire();
85 void hazptrRelease(hazptr_rec*) noexcept;
86 int pushRetired(hazptr_obj* head, hazptr_obj* tail, int count);
87 bool reachedThreshold(int rcount);
88 void tryBulkReclaim();
92 /** Get the default hazptr_domain */
93 hazptr_domain& default_hazptr_domain();
95 extern hazptr_domain default_domain_;
97 /** Free-function retire, that operates on the default domain */
98 template <typename T, typename D = std::default_delete<T>>
99 void hazptr_retire(T* obj, D reclaim = {});
101 /** Definition of hazptr_obj */
103 friend class hazptr_domain;
104 template <typename, typename>
105 friend class hazptr_obj_base;
106 template <typename, typename>
107 friend class hazptr_obj_base_refcounted;
108 friend struct hazptr_priv;
110 void (*reclaim_)(hazptr_obj*);
113 const void* getObjPtr() const;
116 /** Definition of hazptr_obj_base */
117 template <typename T, typename D = std::default_delete<T>>
118 class hazptr_obj_base : public hazptr_obj {
120 /* Retire a removed object and pass the responsibility for
121 * reclaiming it to the hazptr library */
122 void retire(hazptr_domain& domain = default_hazptr_domain(), D reclaim = {});
128 /** Definition of hazptr_recounted_obj_base */
129 template <typename T, typename D = std::default_delete<T>>
130 class hazptr_obj_base_refcounted : public hazptr_obj {
132 /* Retire a removed object and pass the responsibility for
133 * reclaiming it to the hazptr library */
134 void retire(hazptr_domain& domain = default_hazptr_domain(), D reclaim = {});
136 /* aquire_ref() increments the reference count
138 * acquire_ref_safe() is the same as acquire_ref() except that in
139 * addition the caller guarantees that the call is made in a
140 * thread-safe context, e.g., the object is not yet shared. This is
141 * just an optimization to save an atomic operation.
143 * release_ref() decrements the reference count and returns true if
144 * the object is safe to reclaim.
147 void acquire_ref_safe();
151 std::atomic<uint32_t> refcount_{0};
155 /** hazptr_holder: Class for automatic acquisition and release of
156 * hazard pointers, and interface for hazard pointer operations. */
157 class hazptr_holder {
159 friend class hazptr_array;
161 friend class hazptr_local;
164 /* Constructor automatically acquires a hazard pointer. */
165 explicit hazptr_holder(hazptr_domain& domain = default_hazptr_domain());
166 /* Construct an empty hazptr_holder. */
167 // Note: This diverges from the proposal in P0233R4
168 explicit hazptr_holder(std::nullptr_t) noexcept;
170 /* Destructor automatically clears and releases the owned hazard pointer. */
173 hazptr_holder(const hazptr_holder&) = delete;
174 hazptr_holder& operator=(const hazptr_holder&) = delete;
175 // Note: This diverges from the proposal in P0233R4 which disallows
176 // move constructor and assignment operator.
177 hazptr_holder(hazptr_holder&&) noexcept;
178 hazptr_holder& operator=(hazptr_holder&&) noexcept;
180 /** Hazard pointer operations */
181 /* Returns a protected pointer from the source */
182 template <typename T>
183 T* get_protected(const std::atomic<T*>& src) noexcept;
184 /* Returns a protected pointer from the source, filtering
185 the protected pointer through function Func. Useful for
186 stealing bits of the pointer word */
187 template <typename T, typename Func>
188 T* get_protected(const std::atomic<T*>& src, Func f) noexcept;
189 /* Return true if successful in protecting ptr if src == ptr after
190 * setting the hazard pointer. Otherwise sets ptr to src. */
191 template <typename T>
192 bool try_protect(T*& ptr, const std::atomic<T*>& src) noexcept;
193 /* Return true if successful in protecting ptr if src == ptr after
194 * setting the hazard pointer, filtering the pointer through Func.
195 * Otherwise sets ptr to src. */
196 template <typename T, typename Func>
197 bool try_protect(T*& ptr, const std::atomic<T*>& src, Func f) noexcept;
198 /* Set the hazard pointer to ptr */
199 template <typename T>
200 void reset(const T* ptr) noexcept;
201 /* Set the hazard pointer to nullptr */
202 void reset(std::nullptr_t = nullptr) noexcept;
204 /* Swap ownership of hazard pointers between hazptr_holder-s. */
205 /* Note: The owned hazard pointers remain unmodified during the swap
206 * and continue to protect the respective objects that they were
207 * protecting before the swap, if any. */
208 void swap(hazptr_holder&) noexcept;
211 hazptr_domain* domain_;
215 void swap(hazptr_holder&, hazptr_holder&) noexcept;
217 using aligned_hazptr_holder = typename std::
218 aligned_storage<sizeof(hazptr_holder), alignof(hazptr_holder)>::type;
221 * hazptr_array: Optimized for bulk construction and destruction of
224 * WARNING: Do not move from or to individual hazptr_holder-s.
225 * Only move the whole hazptr_array.
227 template <size_t M = 1>
229 static_assert(M > 0, "M must be a positive integer.");
233 explicit hazptr_array(std::nullptr_t) noexcept;
235 hazptr_array(const hazptr_array&) = delete;
236 hazptr_array& operator=(const hazptr_array&) = delete;
237 hazptr_array(hazptr_array&& other) noexcept;
238 hazptr_array& operator=(hazptr_array&& other) noexcept;
242 hazptr_holder& operator[](size_t i) noexcept;
245 aligned_hazptr_holder raw_[M];
250 * hazptr_local: Optimized for construction and destruction of
251 * one or more hazptr_holder-s with local scope.
253 * WARNING 1: Do not move from or to individual hazptr_holder-s.
255 * WARNING 2: There can only be one hazptr_local active for the same
256 * thread at any time. This is not tracked and checked by the
257 * implementation because it would negate the performance gains of
260 template <size_t M = 1>
262 static_assert(M > 0, "M must be a positive integer.");
266 hazptr_local(const hazptr_local&) = delete;
267 hazptr_local& operator=(const hazptr_local&) = delete;
268 hazptr_local(hazptr_local&&) = delete;
269 hazptr_local& operator=(hazptr_local&&) = delete;
273 hazptr_holder& operator[](size_t i) noexcept;
276 aligned_hazptr_holder raw_[M];
277 bool need_destruct_{false};
280 } // namespace hazptr
283 #include "hazptr-impl.h"