memory_allocator.h

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// Copyright 2021 The gRPC Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
#ifndef GRPC_EVENT_ENGINE_MEMORY_ALLOCATOR_H
#define GRPC_EVENT_ENGINE_MEMORY_ALLOCATOR_H
 
#include <stdlib.h>  // for abort()
 
#include <algorithm>
#include <memory>
#include <type_traits>
#include <vector>
 
#include <grpc/event_engine/internal/memory_allocator_impl.h>
#include <grpc/slice.h>
#include <grpc/support/port_platform.h>
 
namespace grpc_event_engine {
namespace experimental {
 
// Tracks memory allocated by one system.
// Is effectively a thin wrapper/smart pointer for a MemoryAllocatorImpl,
// providing a convenient and stable API.
class MemoryAllocator {
 public:
  explicit MemoryAllocator(
      std::shared_ptr<internal::MemoryAllocatorImpl> allocator)
      : allocator_(std::move(allocator)) {}
  // Construct an invalid MemoryAllocator.
  MemoryAllocator() : allocator_(nullptr) {}
  ~MemoryAllocator() {
    if (allocator_ != nullptr) allocator_->Shutdown();
  }
 
  MemoryAllocator(const MemoryAllocator&) = delete;
  MemoryAllocator& operator=(const MemoryAllocator&) = delete;
 
  MemoryAllocator(MemoryAllocator&&) = default;
  MemoryAllocator& operator=(MemoryAllocator&&) = default;
 
  void Reset() {
    auto a = std::move(allocator_);
    if (a != nullptr) a->Shutdown();
  }
 
  size_t Reserve(MemoryRequest request) { return allocator_->Reserve(request); }
 
  void Release(size_t n) { return allocator_->Release(n); }
 
  //
  // The remainder of this type are helper functions implemented in terms of
  // Reserve/Release.
  //
 
  class Reservation {
   public:
    Reservation() = default;
    Reservation(const Reservation&) = delete;
    Reservation& operator=(const Reservation&) = delete;
    Reservation(Reservation&&) = default;
    Reservation& operator=(Reservation&&) = default;
    ~Reservation() {
      if (allocator_ != nullptr) allocator_->Release(size_);
    }
 
   private:
    friend class MemoryAllocator;
    Reservation(std::shared_ptr<internal::MemoryAllocatorImpl> allocator,
                size_t size)
        : allocator_(std::move(allocator)), size_(size) {}
 
    std::shared_ptr<internal::MemoryAllocatorImpl> allocator_;
    size_t size_ = 0;
  };
 
  Reservation MakeReservation(MemoryRequest request) {
    return Reservation(allocator_, Reserve(request));
  }
 
  template <typename T, typename... Args>
  typename std::enable_if<std::has_virtual_destructor<T>::value, T*>::type New(
      Args&&... args) {
    // Wrap T such that when it's destroyed, we can release memory back to the
    // allocator.
    class Wrapper final : public T {
     public:
      explicit Wrapper(std::shared_ptr<internal::MemoryAllocatorImpl> allocator,
                       Args&&... args)
          : T(std::forward<Args>(args)...), allocator_(std::move(allocator)) {}
      ~Wrapper() override { allocator_->Release(sizeof(*this)); }
 
     private:
      const std::shared_ptr<internal::MemoryAllocatorImpl> allocator_;
    };
    Reserve(sizeof(Wrapper));
    return new Wrapper(allocator_, std::forward<Args>(args)...);
  }
 
  template <typename T, typename... Args>
  std::unique_ptr<T> MakeUnique(Args&&... args) {
    return std::unique_ptr<T>(New<T>(std::forward<Args>(args)...));
  }
 
  grpc_slice MakeSlice(MemoryRequest request) {
    return allocator_->MakeSlice(request);
  }
 
  template <typename T>
  class Container {
   public:
    using value_type = T;
 
    explicit Container(MemoryAllocator* underlying_allocator)
        : underlying_allocator_(underlying_allocator) {}
    template <typename U>
    explicit Container(const Container<U>& other)
        : underlying_allocator_(other.underlying_allocator()) {}
 
    MemoryAllocator* underlying_allocator() const {
      return underlying_allocator_;
    }
 
    T* allocate(size_t n) {
      underlying_allocator_->Reserve(n * sizeof(T));
      return static_cast<T*>(::operator new(n * sizeof(T)));
    }
    void deallocate(T* p, size_t n) {
      ::operator delete(p);
      underlying_allocator_->Release(n * sizeof(T));
    }
 
   private:
    MemoryAllocator* underlying_allocator_;
  };
 
 protected:
  internal::MemoryAllocatorImpl* get_internal_impl_ptr() {
    return allocator_.get();
  }
 
  const internal::MemoryAllocatorImpl* get_internal_impl_ptr() const {
    return allocator_.get();
  }
 
 private:
  std::shared_ptr<internal::MemoryAllocatorImpl> allocator_;
};
 
// Wrapper type around std::vector to make initialization against a
// MemoryAllocator based container allocator easy.
template <typename T>
class Vector : public std::vector<T, MemoryAllocator::Container<T>> {
 public:
  explicit Vector(MemoryAllocator* allocator)
      : std::vector<T, MemoryAllocator::Container<T>>(
            MemoryAllocator::Container<T>(allocator)) {}
};
 
class MemoryAllocatorFactory {
 public:
  virtual ~MemoryAllocatorFactory() = default;
  virtual MemoryAllocator CreateMemoryAllocator(absl::string_view name) = 0;
};
 
}  // namespace experimental
}  // namespace grpc_event_engine
 
#endif  // GRPC_EVENT_ENGINE_MEMORY_ALLOCATOR_H