code: def launch_plasma(self, object_store_memory="2g"):
      import atexit
  
      atexit.register(self.shutdown_plasma)
      # TODO: Or can use spark to launch plasma
      from bigdl.orca.ray.utils import resource_to_bytes
  
      self.plasma_path = "/".join(
          sys.executable.split("/")[:-1] + ["plasma_store"]
      )
      self.object_store_memory = resource_to_bytes(object_store_memory)
      self.object_store_address = "/tmp/bigdl_plasma"
      command = "{} -m {} -s {}".format(
          self.plasma_path,
          self.object_store_memory,
          self.object_store_address,
      )
      for host in self.hosts:
          if host != get_node_ip():
              p = subprocess.Popen(
                  ["ssh", "root@{}".format(host), command]
              )
          else:
              p = subprocess.Popen(command.split())
          print("Plasma launched on {}".format(host))
      return self.object_store_address
  
file_path: BigDL/python/orca/src/bigdl/orca/learn/mpi/mpi_runner.py
imports: import os
  import sys
  import subprocess
  import getpass
  from bigdl.dllib.utils.utils import get_node_ip
  from bigdl.dllib.utils.log4Error import *
label_desc: Use image node_id 4 for calling the MPIRunner obj's underlying member method code with example usage: obj.launch_plasma(object_store_memory) and returns: self