class_docstr: Thread-safe store for node reservations.
  
  Args:
    :required: expected number of nodes in the cluster.
code: def __init__(self, required):
      self.required = required
      self.lock = threading.RLock()
      self.reservations = []
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import nested_scopes
  from __future__ import print_function
  import logging
  import os
  import pickle
  import select
  import socket
  import struct
  import sys
  import threading
  import time
  from .None import util
label_desc: Use image node_id 1 to create a new Reservations object  with example: obj = Reservations(required)