code: def initialize_tpu_system(use_megacore=False):
      """Initializes the TPU system."""
  
      # Make sure the server change is fully propagated before attempting to run
      # the core ID merging logic below.
      context.ensure_initialized()
      context.async_wait()
      context.context()._clear_caches()  # pylint: disable=protected-access
  
      use_tfrt_host_runtime = context.context().use_tfrt
      logging.info(
          "Using TFRT host runtime is set to %s", use_tfrt_host_runtime
      )
      try:
          task_id = config.client_id()
          num_tasks = config.num_clients()
          num_devices = config.num_global_devices(_TPU_DEVICE_TYPE)
  
          tpu_topology, device = tpu_system_init_helper(
              task_id,
              num_tasks,
              num_devices,
              use_tfrt_host_runtime=use_tfrt_host_runtime,
              use_megacore=use_megacore,
          )
          global _tpu_topology
          _tpu_topology = tpu_topology
          logging.vlog(
              1,
              "TPU Topology: %s, %s",
              tpu_topology.mesh_shape,
              tpu_topology.device_coordinates,
          )
  
          global _dtensor_device
          _dtensor_device = device
  
          context.async_wait()
  
      except errors.InvalidArgumentError as e:
          raise errors.NotFoundError(
              None,
              None,
              "Initialization failed, no valid TPUs found. " + str(e),
          ) from e
  
      except errors.InternalError as e:
          logging.error(
              "Hit internal error during TPU system initialization. "
              + "It is likely hardware failure. \nPlease check the error "
              + "messages above to see whether that's the case. \nIf so, "
              + "consider to restart the job or try another machine."
          )
          raise e
  
      # Clear out the eager context caches since the memory is invalid now.
      logging.info("Clearing out eager caches")
      context.context()._clear_caches()
  
imports: import functools
  import time
  from typing import List, Optional, Dict
  import numpy
  from tensorflow.dtensor.python import config
  from tensorflow.dtensor.python import dtensor_device
  from tensorflow.dtensor.python import gen_dtensor_ops
  from tensorflow.dtensor.python import layout
  from tensorflow.python.eager import context
  from tensorflow.python.eager import def_function
  from tensorflow.python.framework import constant_op
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.tpu import topology
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 5 for calling a global function with example usage: initialize_tpu_system(use_megacore) without return types