==================== FAILURES ====================
                     ___ EngineTest.test_multiprocess_engine_multi ____
                     
                     self = <pants_test.engine.exp.test_engine.EngineTest testMethod=test_multiprocess_engine_multi>
                     
                         def test_multiprocess_engine_multi(self):
                           with self.multiprocessing_engine() as engine:
                     >       self.assert_engine(engine)
                     
                     tests/python/pants_test/engine/exp/test_engine.py:51: 
                     _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
                     tests/python/pants_test/engine/exp/test_engine.py:32: in assert_engine
                         result = engine.execute(self.request(['compile'], self.java))
                     .pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/engine.py:86: in execute
                         self.reduce(execution_request)
                     .pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/engine.py:273: in reduce
                         await_one()
                     _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
                     
                         def await_one():
                           """Await one completed step, and remove it from in_flight."""
                           if not in_flight:
                             raise Exception('Awaited an empty pool!')
                           step_id, result = self._pool.await_one_result()
                           if isinstance(result, Exception):
                     >       raise result
                     E       UnpicklingError: unpickling stack underflow
                     
                     .pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/engine.py:251: UnpicklingError
                     -------------- Captured stderr call --------------
                     WARN:pants.engine.exp.engine:Traceback (most recent call last):
                       File "/home/travis/build/pantsbuild/pants/.pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/engine.py", line 168, in _execute_step
                         return (step_id, execute())
                       File "/home/travis/build/pantsbuild/pants/.pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/engine.py", line 160, in execute
                         resolved_request = storage.resolve_request(step)
                       File "/home/travis/build/pantsbuild/pants/.pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/storage.py", line 269, in resolve_request
                         dependencies[self._from_key(dep)] = self._from_key(state)
                       File "/home/travis/build/pantsbuild/pants/.pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/storage.py", line 285, in _from_key
                         return self.get(obj)
                       File "/home/travis/build/pantsbuild/pants/.pants.d/python-setup/chroots/05fe564404c4d071f5fd14da3960c8924190161c/pants/engine/exp/storage.py", line 210, in get
                         return self._assert_type_matches(pickle.load(value), key.type)
                     UnpicklingError: unpickling stack underflow
                     
                      1 failed, 872 passed, 1 xfailed, 2 xpassed, 4 warnings in 294.79 seconds

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