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tdlib-fork/tdutils/td/utils/ObjectPool.h

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//
// Copyright Aliaksei Levin (levlam@telegram.org), Arseny Smirnov (arseny30@gmail.com) 2014-2019
//
// 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 <atomic>
#include <memory>
#include <utility>
namespace td {
// It is draft object pool implementaion
//
// Compared with std::shared_ptr:
// + WeakPtr are much faster. Just pointer copy. No barriers, no atomics.
// - We can't destroy object, because we don't know if it is pointed to by some weak pointer
//
template <class DataT>
class ObjectPool {
struct Storage;
public:
class WeakPtr {
public:
WeakPtr() : generation_(-1), storage_(nullptr) {
}
WeakPtr(int32 generation, Storage *storage) : generation_(generation), storage_(storage) {
}
DataT &operator*() const {
return storage_->data;
}
DataT *operator->() const {
return &**this;
}
// Pattern of usage: 1. Read an object 2. Check if read was valid via is_alive
//
// It is not very usual case of acquire/release use.
// Instead of publishing an object via some flag we do the opposite.
// We publish new generation via destruction of the data.
// In usual case if we see a flag, then we are able to use an object.
// In our case if we have used an object and it is already invalid, then generation will mismatch
bool is_alive() const {
if (!storage_) {
return false;
}
std::atomic_thread_fence(std::memory_order_acquire);
return generation_ == storage_->generation.load(std::memory_order_relaxed);
}
// Used for ActorId
bool is_alive_unsafe() const {
if (!storage_) {
return false;
}
return generation_ == storage_->generation.load(std::memory_order_relaxed);
}
bool empty() const {
return storage_ == nullptr;
}
void clear() {
generation_ = -1;
storage_ = nullptr;
}
int32 generation() {
return generation_;
}
private:
int32 generation_;
Storage *storage_;
};
class OwnerPtr {
public:
OwnerPtr() = default;
OwnerPtr(const OwnerPtr &) = delete;
OwnerPtr &operator=(const OwnerPtr &) = delete;
OwnerPtr(OwnerPtr &&other) : storage_(other.storage_), parent_(other.parent_) {
other.storage_ = nullptr;
other.parent_ = nullptr;
}
OwnerPtr &operator=(OwnerPtr &&other) {
if (this != &other) {
storage_ = other.storage_;
parent_ = other.parent_;
other.storage_ = nullptr;
other.parent_ = nullptr;
}
return *this;
}
~OwnerPtr() {
reset();
}
DataT *get() {
return &storage_->data;
}
DataT &operator*() {
return *get();
}
DataT *operator->() {
return get();
}
const DataT *get() const {
return &storage_->data;
}
const DataT &operator*() const {
return *get();
}
const DataT *operator->() const {
return get();
}
WeakPtr get_weak() {
return WeakPtr(storage_->generation.load(std::memory_order_relaxed), storage_);
}
int32 generation() {
return storage_->generation.load(std::memory_order_relaxed);
}
Storage *release() {
auto result = storage_;
storage_ = nullptr;
return result;
}
bool empty() const {
return storage_ == nullptr;
}
void reset() {
if (storage_ != nullptr) {
// for crazy cases when data owns owner pointer to itself.
auto tmp = storage_;
storage_ = nullptr;
parent_->release(OwnerPtr(tmp, parent_));
}
}
private:
friend class ObjectPool;
OwnerPtr(Storage *storage, ObjectPool<DataT> *parent) : storage_(storage), parent_(parent) {
}
Storage *storage_ = nullptr;
ObjectPool<DataT> *parent_ = nullptr;
};
template <class... ArgsT>
OwnerPtr create(ArgsT &&... args) {
Storage *storage = get_storage();
storage->init_data(std::forward<ArgsT>(args)...);
return OwnerPtr(storage, this);
}
OwnerPtr create_empty() {
Storage *storage = get_storage();
return OwnerPtr(storage, this);
}
void set_check_empty(bool flag) {
check_empty_flag_ = flag;
}
void release(OwnerPtr &&owner_ptr) {
Storage *storage = owner_ptr.release();
storage->destroy_data();
release_storage(storage);
}
ObjectPool() = default;
ObjectPool(const ObjectPool &) = delete;
ObjectPool &operator=(const ObjectPool &) = delete;
ObjectPool(ObjectPool &&other) = delete;
ObjectPool &operator=(ObjectPool &&other) = delete;
~ObjectPool() {
while (head_.load()) {
auto to_delete = head_.load();
head_ = to_delete->next;
delete to_delete;
storage_count_--;
}
LOG_CHECK(storage_count_.load() == 0) << storage_count_.load();
}
private:
struct Storage {
// union {
DataT data;
//};
Storage *next = nullptr;
std::atomic<int32> generation{1};
template <class... ArgsT>
void init_data(ArgsT &&... args) {
// new (&data) DataT(std::forward<ArgsT>(args)...);
data = DataT(std::forward<ArgsT>(args)...);
}
void destroy_data() {
generation.fetch_add(1, std::memory_order_relaxed);
std::atomic_thread_fence(std::memory_order_release);
data.clear();
}
};
std::atomic<int32> storage_count_{0};
std::atomic<Storage *> head_{static_cast<Storage *>(nullptr)};
bool check_empty_flag_ = false;
// TODO(perf): allocation Storages in chunks? Anyway we won't be able to release them.
// TODO(perf): memory order
// TODO(perf): use another non lockfree list for release on the same thread
// only one thread, so no aba problem
Storage *get_storage() {
if (head_.load() == nullptr) {
storage_count_++;
return new Storage();
}
Storage *res;
while (true) {
res = head_.load();
auto *next = res->next;
if (head_.compare_exchange_weak(res, next)) {
break;
}
}
return res;
}
// release can be called from other thread
void release_storage(Storage *storage) {
while (true) {
auto *save_head = head_.load();
storage->next = save_head;
if (head_.compare_exchange_weak(save_head, storage)) {
break;
}
}
}
};
} // namespace td