Fixed memory leak with cv method

Author: ankane

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.4.4 (unreleased)
+
+- Fixed memory leak with `cv` method
+
 ## 0.4.3 (2025-06-26)
 
 - Added ARM shared library for Linux

lib/lightgbm/booster.rb

@@ -5,6 +5,8 @@ class Booster
     attr_accessor :best_iteration, :train_data_name, :params
 
     def initialize(params: nil, train_set: nil, model_file: nil, model_str: nil)
+      @refs = []
+
       if model_str
         model_from_string(model_str)
       elsif model_file
@@ -23,6 +25,7 @@ def initialize(params: nil, train_set: nil, model_file: nil, model_str: nil)
         create_handle do |handle|
           safe_call FFI.LGBM_BoosterCreate(train_set.handle, params_str(params), handle)
         end
+        @refs << train_set
       end
 
       self.best_iteration = -1
@@ -33,6 +36,7 @@ def initialize(params: nil, train_set: nil, model_file: nil, model_str: nil)
 
     def add_valid(data, name)
       safe_call FFI.LGBM_BoosterAddValidData(@handle, data.handle)
+      @refs << data
       @name_valid_sets << name
       self # consistent with Python API
     end

lib/lightgbm/dataset.rb

@@ -183,11 +183,7 @@ def construct
 
         safe_call FFI.LGBM_DatasetCreateFromMat(c_data, FFI::C_API_DTYPE_FLOAT64, nrow, ncol, 1, parameters, reference, handle)
       end
-      if used_indices
-        @handle = handle.read_pointer
-      else
-        @handle = ::FFI::AutoPointer.new(handle.read_pointer, FFI.method(:LGBM_DatasetFree))
-      end
+      @handle = ::FFI::AutoPointer.new(handle.read_pointer, FFI.method(:LGBM_DatasetFree))
 
       self.label = @label if @label
       self.weight = @weight if @weight