human
Solve the following python programming problem given the following code:
def _waitpid(self) : 
    '
        Create an executor that waits and handles process termination.
        ' 
    def wait_for_finished() : 
        ' Wait for PID in executor. ' 
        os.waitpid (self.pid, 0) 
        self.eventloop.call_from_executor (done) 
def done() : 
        ' PID received. Back in the main thread. ' 
        os.close (self.master) 
        self.eventloop.remove_reader (self.master) 
        self.master = None 
        self.is_terminated = True 
        self.done_callback () 
self.eventloop.run_in_executor (<MASK>) 
    
    Given the code above, what is a proper replacement for <MASK>?
assistant
#Here is a proper replacement for <MASK>.
def wait_for_finished(