80 lines
1.6 KiB
C++
80 lines
1.6 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 "td/utils/port/thread.h"
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#include <atomic>
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#include <cstring>
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#include <type_traits>
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namespace td {
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template <class T>
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class AtomicRead {
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public:
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void read(T &dest) const {
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while (true) {
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static_assert(std::is_trivially_copyable<T>::value, "T must be trivially copyable");
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auto version_before = version.load();
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if (version_before % 2 == 0) {
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std::memcpy(&dest, &value, sizeof(dest));
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auto version_after = version.load();
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if (version_before == version_after) {
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break;
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}
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}
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td::this_thread::yield();
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}
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}
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struct Write {
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explicit Write(AtomicRead *read) {
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read->do_lock();
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ptr.reset(read);
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}
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struct Destructor {
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void operator()(AtomicRead *read) const {
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read->do_unlock();
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}
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};
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T &operator*() {
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return value();
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}
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T *operator->() {
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return &value();
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}
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T &value() {
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CHECK(ptr);
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return ptr->value;
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}
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private:
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std::unique_ptr<AtomicRead, Destructor> ptr;
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};
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Write lock() {
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return Write(this);
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}
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private:
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std::atomic<uint64> version{0};
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T value;
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void do_lock() {
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bool is_locked = ++version % 2 == 1;
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CHECK(is_locked);
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}
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void do_unlock() {
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bool is_unlocked = ++version % 2 == 0;
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CHECK(is_unlocked);
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}
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};
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} // namespace td
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