// For LLVM style RTTI.
  static bool classof(const AbstractOperation* ptr) {
    return ptr->getKind() == kGraph || ptr->getKind() == kMlir;
  }
};

namespace internal {
struct TracingOperationDeleter {
  void operator()(TracingOperation* p) const {
    if (p != nullptr) {
      p->Release();
    }
  }
};
}  // namespace internal

using TracingOperationPtr =

      : AbstractContext(kind) {}
  ~ImmediateExecutionContext() override {}
};

namespace internal {
struct ImmediateExecutionContextDeleter {
  void operator()(ImmediateExecutionContext* p) const {
    if (p != nullptr) {
      p->Release();
    }
  }
};
}  // namespace internal

using ImmediateContextPtr =
    std::unique_ptr<ImmediateExecutionContext,

// it will be stopped and joined.
TF_CAPI_EXPORT extern void TF_DeleteServer(TF_Server* server);

// Register a listener method that processes printed messages.
//
// If any listeners are registered, the print operator will call all listeners
// with the printed messages and immediately return without writing to the
// logs.
TF_CAPI_EXPORT extern void TF_RegisterLogListener(
    void (*listener)(const char*));

void ForwardAccumulator<Gradient, BackwardFunction, TapeTensor>::Watch(
    int64_t tensor_id, Gradient* tangent) {
  typename std::unordered_map<int64_t, Gradient*>::iterator existing =
      accumulated_gradients_.find(tensor_id);
  vspace_.MarkAsResult(tangent);
  if (existing == accumulated_gradients_.end()) {
    accumulated_gradients_.emplace(tensor_id, tangent);
  } else {

  /// mu_.
  struct Block {
    /// The block data.
    std::vector<char> data;
    /// A list iterator pointing to the block's position in the LRU list.
    std::list<Key>::iterator lru_iterator;
    /// A list iterator pointing to the block's position in the LRA list.
    std::list<Key>::iterator lra_iterator;
    /// The timestamp (seconds since epoch) at which the block was cached.
    uint64_t timestamp;