class_docstr: Python TaskScheduler object.
  
  This is the simplest object that supports msg_id based
  DAG dependencies. *Only* task msg_ids are checked, not
  msg_ids of jobs submitted via the MUX queue.
class_docstr_tok: ["Python","TaskScheduler","object",".","This","is","the","simplest","object","that","supports","msg_id","based","DAG","dependencies",".","*","Only","*","task","msg_ids","are","checked",",","not","msg_ids","of","jobs","submitted","via","the","MUX","queue","."]
docstr: handle an unmet dependency
docstr_tok: ["handle","an","unmet","dependency"]
code: def handle_unmet_dependency(self, idents, parent):
      """handle an unmet dependency"""
      engine = idents[0]
      msg_id = parent["msg_id"]
  
      job = self.pending[engine].pop(msg_id)
      job.blacklist.add(engine)
  
      if job.blacklist == job.targets:
          self.queue_map[msg_id] = job
          self.fail_unreachable(msg_id)
      elif not self.maybe_run(job):
          # resubmit failed
          if msg_id not in self.all_failed:
              # put it back in our dependency tree
              self.save_unmet(job)
  
      if self.hwm:
          try:
              idx = self.targets.index(engine)
          except ValueError:
              pass  # skip load-update for dead engines
          else:
              if self.loads[idx] == self.hwm - 1:
                  self.update_graph(None)
  
imports: import time
  from collections import deque
  from random import randint, random
  from types import FunctionType
  import zmq
  from traitlets import Dict, Enum, Instance, Integer, List, observe
  from ipyparallel import Dependency, error, util
  from ipyparallel.controller.scheduler import Scheduler
label_desc: Use image node_id 19 for calling the TaskScheduler obj's underlying member method code with example usage: obj.handle_unmet_dependency(idents, parent) without return types