code: def unlock(self):
      self.counter.next(-1)
  
file_path: mpi4py/demo/nxtval/nxtval-mpi3.py
imports: from mpi4py import MPI
  from array import array
  import struct
label_desc: Use image node_id 6 for calling the Mutex obj's underlying member method code with example usage: obj.unlock() without return types