Class SliceAllocator

native/thirdpart/flatbuffers/grpc.h:84–149

SliceAllocator is a gRPC-specific allocator that uses the `grpc_slice` refcounted slices to manage memory ownership. This makes it easy and efficient to transfer buffers to gRPC.

// refcounted slices to manage memory ownership. This makes it easy and
// efficient to transfer buffers to gRPC.
class SliceAllocator : public Allocator {
 public:
  SliceAllocator() : slice_(grpc_empty_slice()) {}

  SliceAllocator(const SliceAllocator &other) = delete;
  SliceAllocator &operator=(const SliceAllocator &other) = delete;

  SliceAllocator(SliceAllocator &&other) : slice_(grpc_empty_slice()) {
    // default-construct and swap idiom
    swap(other);
  }

  SliceAllocator &operator=(SliceAllocator &&other) {
    // move-construct and swap idiom
    SliceAllocator temp(std::move(other));
    swap(temp);
    return *this;
  }

  void swap(SliceAllocator &other) {
    using std::swap;
    swap(slice_, other.slice_);
  }

  virtual ~SliceAllocator() { grpc_slice_unref(slice_); }

  virtual uint8_t *allocate(size_t size) override {
    FLATBUFFERS_ASSERT(GRPC_SLICE_IS_EMPTY(slice_));
    slice_ = grpc_slice_malloc(size);
    return GRPC_SLICE_START_PTR(slice_);
  }

  virtual void deallocate(uint8_t *p, size_t size) override {
    FLATBUFFERS_ASSERT(p == GRPC_SLICE_START_PTR(slice_));
    FLATBUFFERS_ASSERT(size == GRPC_SLICE_LENGTH(slice_));
    grpc_slice_unref(slice_);
    slice_ = grpc_empty_slice();
  }

  virtual uint8_t *reallocate_downward(uint8_t *old_p, size_t old_size,
                                       size_t new_size, size_t in_use_back,
                                       size_t in_use_front) override {
    FLATBUFFERS_ASSERT(old_p == GRPC_SLICE_START_PTR(slice_));
    FLATBUFFERS_ASSERT(old_size == GRPC_SLICE_LENGTH(slice_));
    FLATBUFFERS_ASSERT(new_size > old_size);
    grpc_slice old_slice = slice_;
    grpc_slice new_slice = grpc_slice_malloc(new_size);
    uint8_t *new_p = GRPC_SLICE_START_PTR(new_slice);
    memcpy_downward(old_p, old_size, new_p, new_size, in_use_back,
                    in_use_front);
    slice_ = new_slice;
    grpc_slice_unref(old_slice);
    return new_p;
  }

 private:
  grpc_slice &get_slice(uint8_t *p, size_t size) {
    FLATBUFFERS_ASSERT(p == GRPC_SLICE_START_PTR(slice_));