How to use the mpipool.core._function_wrapper function in mpipool

"""
        ntask = len(tasks)

        # If not the master just wait for instructions.
        if not self.is_master():
            self.wait()
            return

        if function is not self.function:
            if self.debug:
                print("Master replacing pool function with {0}."
                      .format(function))

            self.function = function
            F = _function_wrapper(function)

            # Tell all the workers what function to use.
            requests = []
            for i in range(self.size):
                r = self.comm.isend(F, dest=i + 1)
                requests.append(r)

            # Wait until all of the workers have responded. See:
            #       https://gist.github.com/4176241
            MPI.Request.waitall(requests)

        if (not self.loadbalance) or (ntask <= self.size):
            # Do not perform load-balancing - the default load-balancing
            # scheme emcee uses.

            # Send all the tasks off and wait for them to be received.

# Blocking receive to wait for instructions.
            task = self.comm.recv(source=0, tag=MPI.ANY_TAG, status=status)
            if self.debug:
                print("Worker {0} got task {1} with tag {2}."
                      .format(self.rank, task, status.tag))

            # Check if message is special sentinel signaling end.
            # If so, stop.
            if isinstance(task, _close_pool_message):
                if self.debug:
                    print("Worker {0} told to quit.".format(self.rank))
                break

            # Check if message is special type containing new function
            # to be applied
            if isinstance(task, _function_wrapper):
                self.function = task.function
                if self.debug:
                    print("Worker {0} replaced its task function: {1}."
                          .format(self.rank, self.function))
                continue

            # If not a special message, just run the known function on
            # the input and return it asynchronously.
            try:
                result = self.function(task)
            except:
                tb = traceback.format_exc()
                self.comm.isend(MPIPoolException(tb), dest=0, tag=status.tag)
                return
            if self.debug:
                print("Worker {0} sending answer {1} with tag {2}."