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 resize(self, size, trunc=False):
      self._shm_chunk.resize(size, trunc)
      self.capacity = size
  
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 6 for calling the BufShmChunk obj's underlying member method code with example usage: obj.resize(size, trunc) without return types