tree_updater.h

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#ifndef XGBOOST_TREE_UPDATER_H_
#define XGBOOST_TREE_UPDATER_H_

#include <dmlc/registry.h>
#include <xgboost/base.h> // 用于 Args, GradientPair
#include <xgboost/data.h> // DMatrix
#include <xgboost/host_device_vector.h> // 用于 HostDeviceVector
#include <xgboost/linalg.h> // 用于 VectorView
#include <xgboost/model.h> // 用于 Configurable
#include <xgboost/span.h> // 用于 Span
#include <xgboost/tree_model.h> // 用于 RegTree

#include <functional> // 用于 function
#include <string> // 用于 string
#include <vector> // 用于 vector

namespace xgboost {
namespace tree {
struct TrainParam;
}

class Json;
struct Context;
struct ObjInfo;

/// interface of tree update module, that performs update of a tree.
class TreeUpdater : public Configurable {
 protected
   /// \brief Context for device and RNG.
 Context const* ctx_ = nullptr;
 public
   /// \brief virtual destructor
   /// \brief Initialize the updater with given arguments.
   /// \brief Whether this updater can be used for updating existing trees.
   /// \brief Wether the out_position in Update is valid. This determines whether adaptive tree can be used.
   /// \brief perform update to the tree models
   /// \param param Training parameters.
   /// \param gpair Pointer to the gradient and hessian.
   /// \param data DMatrix object storing the training data.
   /// \brief determines whether updater has enough knowledge about a given dataset to quickly update prediction cache.
   /// \param data DMatrix object.
   /// \param out_preds Output cache.
 return false;
 }
 [[nodiscard]] virtual char const* Name() const = 0;
   /// \brief Create a tree updater given name.
 static TreeUpdater* Create(const std::string& name, Context const* ctx, ObjInfo const* task);
};

/// \brief Registry entry for tree updater.
struct TreeUpdaterReg
 : public dmlc::FunctionRegEntryBase<
 TreeUpdaterReg, std::function<TreeUpdater*(Context const* ctx, ObjInfo const* task)>> {};
/// \brief Register a tree updater.
#define XGBOOST_REGISTER_TREE_UPDATER(UniqueId, Name) \
 static DMLC_ATTRIBUTE_UNUSED ::xgboost::TreeUpdaterReg& \
 __make_ ## TreeUpdaterReg ## _ ## UniqueId ## __ = \
 ::dmlc::Registry< ::xgboost::TreeUpdaterReg>::Get()->__REGISTER__(Name)
} // namespace xgboost
#endif // XGBOOST_TREE_UPDATER_H_