initial commit

tdutils/td/utils/ObjectPool.h

@@ -0,0 +1,261 @@
+/*
+    This file is part of TON Blockchain Library.
+
+    TON Blockchain Library is free software: you can redistribute it and/or modify
+    it under the terms of the GNU Lesser General Public License as published by
+    the Free Software Foundation, either version 2 of the License, or
+    (at your option) any later version.
+
+    TON Blockchain Library is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU Lesser General Public License for more details.
+
+    You should have received a copy of the GNU Lesser General Public License
+    along with TON Blockchain Library.  If not, see <http://www.gnu.org/licenses/>.
+
+    Copyright 2017-2019 Telegram Systems LLP
+*/
+#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