class_docstr: An environment for running on clusters managed by the LSF resource manager.
  
  It is expected that any execution using this ClusterEnvironment was executed
  using the Job Step Manager i.e. ``jsrun``.
  
  This plugin expects the following environment variables:
  
  ``LSB_JOBID``
    The LSF assigned job ID
  
  ``LSB_DJOB_RANKFILE``
    The OpenMPI compatible rank file for the LSF job
  
  ``JSM_NAMESPACE_LOCAL_RANK``
    The node local rank for the task. This environment variable is set by ``jsrun``
  
  ``JSM_NAMESPACE_SIZE``
    The world size for the task. This environment variable is set by ``jsrun``
  
  ``JSM_NAMESPACE_RANK``
    The global rank for the task. This environment variable is set by ``jsrun``
docstr: A helper function for accessing the main port.
  
  Uses the LSF job ID so all ranks can compute the main port.
docstr_tok: ["A","helper","function","for","accessing","the","main","port",".","Uses","the","LSF","job","ID","so","all","ranks","can","compute","the","main","port","."]
code: def _get_main_port() -> int:
      """A helper function for accessing the main port.
  
      Uses the LSF job ID so all ranks can compute the main port.
  
      """
      # check for user-specified main port
      if "MASTER_PORT" in os.environ:
          log.debug(
              f"Using externally specified main port: {os.environ['MASTER_PORT']}"
          )
          return int(os.environ["MASTER_PORT"])
      if "LSB_JOBID" in os.environ:
          port = int(os.environ["LSB_JOBID"])
          # all ports should be in the 10k+ range
          port = port % 1000 + 10000
          log.debug(f"calculated LSF main port: {port}")
          return port
      raise ValueError(
          "Could not find job id in environment variable LSB_JOBID"
      )
  
imports: import logging
  import os
  import socket
  from typing import Dict, List
  from typing_extensions import override
  from lightning.fabric.plugins.environments.cluster_environment import ClusterEnvironment
  from lightning.fabric.utilities.cloud_io import get_filesystem
label_desc: Use image node_id 16 for calling the LSFEnvironment obj's underlying member method code with example usage: obj._get_main_port() and returns: int, port