142 lines
3.9 KiB
C++
142 lines
3.9 KiB
C++
//
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// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2020
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#pragma once
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#include "td/utils/common.h"
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#include <array>
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#include <atomic>
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#include <memory>
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namespace td {
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template <class T, int MaxPointersN = 1, class Deleter = std::default_delete<T>>
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class HazardPointers {
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public:
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explicit HazardPointers(size_t threads_n) : threads_(threads_n) {
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for (auto &data : threads_) {
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for (auto &ptr : data.hazard_) {
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// workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64658
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#if TD_GCC && GCC_VERSION <= 40902
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ptr = nullptr;
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#else
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std::atomic_init(&ptr, static_cast<T *>(nullptr));
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#endif
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}
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}
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}
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HazardPointers(const HazardPointers &other) = delete;
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HazardPointers &operator=(const HazardPointers &other) = delete;
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HazardPointers(HazardPointers &&other) = delete;
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HazardPointers &operator=(HazardPointers &&other) = delete;
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class Holder {
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public:
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template <class S>
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S *protect(std::atomic<S *> &to_protect) {
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return do_protect(hazard_ptr_, to_protect);
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}
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Holder(HazardPointers &hp, size_t thread_id, size_t pos) : Holder(hp.get_hazard_ptr(thread_id, pos)) {
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CHECK(hazard_ptr_.load() == 0);
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hazard_ptr_.store(reinterpret_cast<T *>(1));
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}
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Holder(const Holder &other) = delete;
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Holder &operator=(const Holder &other) = delete;
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Holder(Holder &&other) = delete;
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Holder &operator=(Holder &&other) = delete;
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~Holder() {
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clear();
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}
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void clear() {
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hazard_ptr_.store(nullptr, std::memory_order_release);
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}
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private:
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friend class HazardPointers;
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explicit Holder(std::atomic<T *> &ptr) : hazard_ptr_(ptr) {
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}
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std::atomic<T *> &hazard_ptr_;
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};
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void retire(size_t thread_id, T *ptr = nullptr) {
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CHECK(thread_id < threads_.size());
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auto &data = threads_[thread_id];
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if (ptr) {
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data.to_delete_.push_back(std::unique_ptr<T, Deleter>(ptr));
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}
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for (auto it = data.to_delete_.begin(); it != data.to_delete_.end();) {
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if (!is_protected(it->get())) {
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it->reset();
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it = data.to_delete_.erase(it);
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} else {
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++it;
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}
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}
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}
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// old inteface
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T *protect(size_t thread_id, size_t pos, std::atomic<T *> &ptr) {
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return do_protect(get_hazard_ptr(thread_id, pos), ptr);
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}
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void clear(size_t thread_id, size_t pos) {
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do_clear(get_hazard_ptr(thread_id, pos));
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}
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size_t to_delete_size_unsafe() const {
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size_t res = 0;
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for (auto &thread : threads_) {
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res += thread.to_delete_.size();
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}
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return res;
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}
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private:
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struct ThreadData {
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std::array<std::atomic<T *>, MaxPointersN> hazard_;
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char pad[TD_CONCURRENCY_PAD - sizeof(std::array<std::atomic<T *>, MaxPointersN>)];
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// stupid gc
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std::vector<std::unique_ptr<T, Deleter>> to_delete_;
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char pad2[TD_CONCURRENCY_PAD - sizeof(std::vector<std::unique_ptr<T, Deleter>>)];
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};
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std::vector<ThreadData> threads_;
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char pad2[TD_CONCURRENCY_PAD - sizeof(std::vector<ThreadData>)];
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template <class S>
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static S *do_protect(std::atomic<T *> &hazard_ptr, std::atomic<S *> &to_protect) {
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T *saved = nullptr;
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T *to_save;
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while ((to_save = to_protect.load()) != saved) {
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hazard_ptr.store(to_save);
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saved = to_save;
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}
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return static_cast<S *>(saved);
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}
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static void do_clear(std::atomic<T *> &hazard_ptr) {
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hazard_ptr.store(nullptr, std::memory_order_release);
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}
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bool is_protected(T *ptr) {
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for (auto &thread : threads_) {
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for (auto &hazard_ptr : thread.hazard_) {
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if (hazard_ptr.load() == ptr) {
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return true;
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}
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}
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}
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return false;
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}
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std::atomic<T *> &get_hazard_ptr(size_t thread_id, size_t pos) {
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CHECK(thread_id < threads_.size());
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return threads_[thread_id].hazard_[pos];
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}
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};
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} // namespace td
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