class_docstr: Helper class for building block stats.
  
  When this class is created, we record the start time. When build() is
  called, the time delta is saved as part of the stats.
class_docstr_tok: ["Helper","class","for","building","block","stats",".","When","this","class","is","created",",","we","record","the","start","time",".","When","build","(",")","is","called",",","the","time","delta","is","saved","as","part","of","the","stats","."]
code: def __init__(self):
      self.start_time = time.perf_counter()
      self.start_cpu = time.process_time()
  
imports: import collections
  import os
  import time
  from dataclasses import dataclass
  from typing import TYPE_CHECKING, Callable, Dict, Iterator, List, Literal, Optional, Protocol, Tuple, TypeVar, Union
  import numpy
  import ray
  from ray import DynamicObjectRefGenerator
  from ray.data._internal.util import _check_pyarrow_version, _truncated_repr
  from ray.types import ObjectRef
  from ray.util.annotations import DeveloperAPI
  import psutil
label_desc: Use image node_id 1 to create a new _BlockExecStatsBuilder object  with example: obj = _BlockExecStatsBuilder()