class_docstr: Simple wrapper around shared memory chunks. Adds mem_chunk_id used
  to identify chunks in the communication between parent and worker process.
code: def open_shm(self, handle):
      # self._shm_chunk should be None only as a result of deserialization of the instance.
      # In that case it is not valid to call other methods until shared memory chunk is restored
      # with open_shm call
      assert self._shm_chunk is None
      try:
          self._shm_chunk = shared_mem.SharedMem.open(
              handle, self.capacity
          )
      except:  # noqa: E722
          if handle >= 0:
              os.close(handle)
          raise
  
imports: import os
  from nvidia.dali._multiproc import shared_mem
  from nvidia.dali._multiproc.messages import ShmMessageDesc
  from nvidia.dali._utils.external_source_impl import assert_cpu_sample_data_type, sample_to_numpy
  import pickle
label_desc: Use image node_id 5 for calling the BufShmChunk obj's underlying member method code with example usage: obj.open_shm(handle) without return types