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//
// 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 "td/utils/logging.h"
#include "td/utils/port/sleep.h"
#include <atomic>
#include <memory>
namespace td {
template <class T>
class EpochBasedMemoryReclamation {
public:
EpochBasedMemoryReclamation(const EpochBasedMemoryReclamation &) = delete;
EpochBasedMemoryReclamation &operator=(const EpochBasedMemoryReclamation &) = delete;
EpochBasedMemoryReclamation(EpochBasedMemoryReclamation &&) = delete;
EpochBasedMemoryReclamation &operator=(EpochBasedMemoryReclamation &&) = delete;
~EpochBasedMemoryReclamation() = default;
class Locker {
public:
Locker(size_t thread_id, EpochBasedMemoryReclamation *ebmr) : thread_id_(thread_id), ebmr_(ebmr) {
}
Locker(const Locker &) = delete;
Locker &operator=(const Locker &) = delete;
Locker(Locker &&) = default;
Locker &operator=(Locker &&) = delete;
~Locker() {
if (ebmr_) {
retire_sync();
unlock();
(void)ebmr_.release();
}
}
void lock() {
DCHECK(ebmr_);
ebmr_->lock(thread_id_);
}
void unlock() {
DCHECK(ebmr_);
ebmr_->unlock(thread_id_);
}
void retire_sync() {
ebmr_->retire_sync(thread_id_);
}
void retire() {
ebmr_->retire(thread_id_);
}
void retire(T *ptr) {
ebmr_->retire(thread_id_, ptr);
}
private:
size_t thread_id_;
struct Never {
template <class S>
void operator()(S *) const {
UNREACHABLE();
}
};
std::unique_ptr<EpochBasedMemoryReclamation, Never> ebmr_;
};
explicit EpochBasedMemoryReclamation(size_t threads_n) : threads_(threads_n) {
}
Locker get_locker(size_t thread_id) {
return Locker{thread_id, this};
}
size_t to_delete_size_unsafe() const {
size_t res = 0;
for (auto &thread_data : threads_) {
// LOG(ERROR) << "---" << thread_data.epoch.load() / 2;
for (size_t i = 0; i < MAX_BAGS; i++) {
res += thread_data.to_delete[i].size();
// LOG(ERROR) << thread_data.to_delete[i].size();
}
}
return res;
}
private:
static constexpr size_t MAX_BAGS = 3;
struct ThreadData {
std::atomic<int64> epoch{1};
char pad[TD_CONCURRENCY_PAD - sizeof(std::atomic<int64>)];
size_t to_skip{0};
size_t checked_thread_i{0};
size_t bag_i{0};
std::vector<unique_ptr<T>> to_delete[MAX_BAGS];
char pad2[TD_CONCURRENCY_PAD - sizeof(std::vector<unique_ptr<T>>) * MAX_BAGS];
void rotate_bags() {
bag_i = (bag_i + 1) % MAX_BAGS;
to_delete[bag_i].clear();
}
void set_epoch(int64 new_epoch) {
//LOG(ERROR) << new_epoch;
if (epoch.load(std::memory_order_relaxed) / 2 != new_epoch) {
checked_thread_i = 0;
to_skip = 0;
rotate_bags();
}
epoch = new_epoch * 2;
}
void idle() {
epoch.store(epoch.load(std::memory_order_relaxed) | 1);
}
size_t undeleted() const {
size_t res = 0;
for (size_t i = 0; i < MAX_BAGS; i++) {
res += to_delete[i].size();
}
return res;
}
};
std::vector<ThreadData> threads_;
char pad[TD_CONCURRENCY_PAD - sizeof(std::vector<ThreadData>)];
std::atomic<int64> epoch_{1};
char pad2[TD_CONCURRENCY_PAD - sizeof(std::atomic<int64>)];
void lock(size_t thread_id) {
auto &data = threads_[thread_id];
auto epoch = epoch_.load();
data.set_epoch(epoch);
if (data.to_skip == 0) {
data.to_skip = 30;
step_check(data);
} else {
data.to_skip--;
}
}
void unlock(size_t thread_id) {
//LOG(ERROR) << "UNLOCK";
auto &data = threads_[thread_id];
data.idle();
}
bool step_check(ThreadData &data) {
auto epoch = data.epoch.load(std::memory_order_relaxed) / 2;
auto checked_thread_epoch = threads_[data.checked_thread_i].epoch.load();
if (checked_thread_epoch % 2 == 1 || checked_thread_epoch / 2 == epoch) {
data.checked_thread_i++;
if (data.checked_thread_i == threads_.size()) {
if (epoch_.compare_exchange_strong(epoch, epoch + 1)) {
data.set_epoch(epoch + 1);
} else {
data.set_epoch(epoch);
}
}
return true;
}
return false;
}
void retire_sync(size_t thread_id) {
auto &data = threads_[thread_id];
while (true) {
retire(thread_id);
data.idle();
if (data.undeleted() == 0) {
break;
}
usleep_for(1000);
}
}
void retire(size_t thread_id) {
auto &data = threads_[thread_id];
data.set_epoch(epoch_.load());
while (step_check(data) && data.undeleted() != 0) {
}
}
void retire(size_t thread_id, T *ptr) {
auto &data = threads_[thread_id];
data.to_delete[data.bag_i].push_back(unique_ptr<T>{ptr});
}
};
} // namespace td
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