1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
|
//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2026
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#pragma once
#include "td/utils/common.h"
#include <array>
#include <atomic>
#include <memory>
namespace td {
template <class T, int MaxPointersN = 1, class Deleter = std::default_delete<T>>
class HazardPointers {
public:
explicit HazardPointers(size_t threads_n) : threads_(threads_n) {
for (auto &data : threads_) {
for (auto &ptr : data.hazard_) {
// workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64658
#if TD_GCC && GCC_VERSION <= 40902
ptr = nullptr;
#else
std::atomic_init(&ptr, static_cast<T *>(nullptr));
#endif
}
}
}
HazardPointers(const HazardPointers &) = delete;
HazardPointers &operator=(const HazardPointers &) = delete;
HazardPointers(HazardPointers &&) = delete;
HazardPointers &operator=(HazardPointers &&) = delete;
class Holder {
public:
template <class S>
S *protect(std::atomic<S *> &to_protect) {
return do_protect(hazard_ptr_, to_protect);
}
Holder(HazardPointers &hp, size_t thread_id, size_t pos) : Holder(hp.get_hazard_ptr(thread_id, pos)) {
CHECK(hazard_ptr_.load() == 0);
hazard_ptr_.store(reinterpret_cast<T *>(1));
}
Holder(const Holder &) = delete;
Holder &operator=(const Holder &) = delete;
Holder(Holder &&) = delete;
Holder &operator=(Holder &&) = delete;
~Holder() {
clear();
}
void clear() {
hazard_ptr_.store(nullptr, std::memory_order_release);
}
private:
friend class HazardPointers;
explicit Holder(std::atomic<T *> &ptr) : hazard_ptr_(ptr) {
}
std::atomic<T *> &hazard_ptr_;
};
void retire(size_t thread_id, T *ptr = nullptr) {
CHECK(thread_id < threads_.size());
auto &data = threads_[thread_id];
if (ptr) {
data.to_delete_.push_back(std::unique_ptr<T, Deleter>(ptr));
}
for (auto it = data.to_delete_.begin(); it != data.to_delete_.end();) {
if (!is_protected(it->get())) {
it->reset();
it = data.to_delete_.erase(it);
} else {
++it;
}
}
}
// old interface
T *protect(size_t thread_id, size_t pos, std::atomic<T *> &ptr) {
return do_protect(get_hazard_ptr(thread_id, pos), ptr);
}
void clear(size_t thread_id, size_t pos) {
do_clear(get_hazard_ptr(thread_id, pos));
}
size_t to_delete_size_unsafe() const {
size_t res = 0;
for (auto &thread_data : threads_) {
res += thread_data.to_delete_.size();
}
return res;
}
private:
struct ThreadData {
std::array<std::atomic<T *>, MaxPointersN> hazard_;
char pad[TD_CONCURRENCY_PAD - sizeof(std::array<std::atomic<T *>, MaxPointersN>)];
// stupid gc
std::vector<std::unique_ptr<T, Deleter>> to_delete_;
char pad2[TD_CONCURRENCY_PAD - sizeof(std::vector<std::unique_ptr<T, Deleter>>)];
};
std::vector<ThreadData> threads_;
char pad2[TD_CONCURRENCY_PAD - sizeof(std::vector<ThreadData>)];
template <class S>
static S *do_protect(std::atomic<T *> &hazard_ptr, std::atomic<S *> &to_protect) {
T *saved = nullptr;
T *to_save;
while ((to_save = to_protect.load()) != saved) {
hazard_ptr.store(to_save);
saved = to_save;
}
return static_cast<S *>(saved);
}
static void do_clear(std::atomic<T *> &hazard_ptr) {
hazard_ptr.store(nullptr, std::memory_order_release);
}
bool is_protected(T *ptr) {
for (auto &thread_data : threads_) {
for (auto &hazard_ptr : thread_data.hazard_) {
if (hazard_ptr.load() == ptr) {
return true;
}
}
}
return false;
}
std::atomic<T *> &get_hazard_ptr(size_t thread_id, size_t pos) {
CHECK(thread_id < threads_.size());
return threads_[thread_id].hazard_[pos];
}
};
} // namespace td
|
