class_docstr: Simple fixed capacity shared memory queue of fixed size messages.
  Writing to a full queue fails, attempt to get from an empty queue blocks until data is
  available or the queue is closed.
class_docstr_tok: ["Simple","fixed","capacity","shared","memory","queue","of","fixed","size","messages",".","Writing","to","a","full","queue","fails",",","attempt","to","get","from","an","empty","queue","blocks","until","data","is","available","or","the","queue","is","closed","."]
code: def _init_offsets(self):
      self.msgs_offsets = [
          i * self.msg_size + self.meta_size
          for i in range(self.capacity)
      ]
  
imports: from typing import List, Optional
  import os
  import threading
  from nvidia.dali._multiproc import shared_mem
  from nvidia.dali._multiproc.messages import Structure, ShmMessageDesc
  from nvidia.dali._multiproc.shared_batch import _align_up
label_desc: Use image node_id 4 for calling the ShmQueue obj's underlying member method code with example usage: obj._init_offsets() without return types