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.
18 #include <folly/experimental/hazptr/debug.h>
19 #include <folly/experimental/hazptr/hazptr.h>
24 /** Set implemented as an ordered singly-linked list.
26 * A single writer thread may add or remove elements. Multiple reader
27 * threads may search the set concurrently with each other and with
28 * the writer's operations.
32 template <typename Node>
34 void operator()(Node* p) {
35 DEBUG_PRINT(p << " " << sizeof(Node));
40 class Node : public hazptr_obj_base<Node, Reclaimer<Node>> {
43 std::atomic<Node*> next_;
45 Node(T e, Node* n) : elem_(e), next_(n) {
46 DEBUG_PRINT(this << " " << e << " " << n);
55 std::atomic<Node*> head_ = {nullptr};
57 /* Used by the single writer */
58 void locate_lower_bound(const T& v, std::atomic<Node*>*& prev) const {
59 auto curr = prev->load(std::memory_order_relaxed);
61 if (curr->elem_ >= v) {
64 prev = &(curr->next_);
65 curr = curr->next_.load(std::memory_order_relaxed);
73 for (auto p = head_.load(); p; p = next) {
74 next = p->next_.load();
81 locate_lower_bound(v, prev);
82 auto curr = prev->load(std::memory_order_relaxed);
83 if (curr && curr->elem_ == v) {
86 prev->store(new Node(std::move(v), curr));
90 bool remove(const T& v) {
92 locate_lower_bound(v, prev);
93 auto curr = prev->load(std::memory_order_relaxed);
94 if (!curr || curr->elem_ != v) {
97 Node *curr_next = curr->next_.load();
98 // Patch up the actual list...
99 prev->store(curr_next, std::memory_order_release);
100 // ...and only then null out the removed node.
101 curr->next_.store(nullptr, std::memory_order_release);
106 /* Used by readers */
107 bool contains(const T& val) const {
108 /* Two hazard pointers for hand-over-hand traversal. */
109 hazptr_local<2> hptr;
110 hazptr_holder* hptr_prev = &hptr[0];
111 hazptr_holder* hptr_curr = &hptr[1];
114 auto curr = prev->load(std::memory_order_acquire);
116 if (!curr) { return false; }
117 if (!hptr_curr->try_protect(curr, *prev)) {
120 auto next = curr->next_.load(std::memory_order_acquire);
121 if (prev->load(std::memory_order_acquire) != curr) {
124 if (curr->elem_ == val) {
126 } else if (!(curr->elem_ < val)) {
127 return false; // because the list is sorted
129 prev = &(curr->next_);
131 std::swap(hptr_curr, hptr_prev);
137 } // namespace hazptr