Make ProcessListener instances persistable (#277)

The `ProcessListener` is made persistable by deriving it, as well as the
`EventHelper` class from `persistence.Savable`. The class `EventHelper`
is moved to a new file because of a circular import that would result
between the `utils` and `persistence` modules.

There was a circular reference issue in the test listener that was
storing a reference to the process inside it, making its serialization
impossible. To fix the tests an ugly hack was used: storing the reference
to the process outside the class in a global dict using id as keys. Some
more ugly hacks were needed to correctly check the equality of two
processes. Instances having different listeners should be ignored.

src/plumpy/base/utils.py

@@ -16,6 +16,8 @@ def wrapper(self: Any, *args: Any, **kwargs: Any) -> None:
         wrapped(self, *args, **kwargs)
         self._called -= 1
 
+    # Forward wrapped function name to the decorator to show the correct name in the ``call_with_super_check``
+    wrapper.__name__ = wrapped.__name__
     return wrapper
 
 

src/plumpy/event_helper.py

@@ -0,0 +1,54 @@
+# -*- coding: utf-8 -*-
+import logging
+from typing import TYPE_CHECKING, Any, Callable
+
+from . import persistence
+
+if TYPE_CHECKING:
+    from typing import Set, Type
+
+    from .process_listener import ProcessListener  # pylint: disable=cyclic-import
+
+_LOGGER = logging.getLogger(__name__)
+
+
+@persistence.auto_persist('_listeners', '_listener_type')
+class EventHelper(persistence.Savable):
+
+    def __init__(self, listener_type: 'Type[ProcessListener]'):
+        assert listener_type is not None, 'Must provide valid listener type'
+
+        self._listener_type = listener_type
+        self._listeners: 'Set[ProcessListener]' = set()
+
+    def add_listener(self, listener: 'ProcessListener') -> None:
+        assert isinstance(listener, self._listener_type), 'Listener is not of right type'
+        self._listeners.add(listener)
+
+    def remove_listener(self, listener: 'ProcessListener') -> None:
+        self._listeners.discard(listener)
+
+    def remove_all_listeners(self) -> None:
+        self._listeners.clear()
+
+    @property
+    def listeners(self) -> 'Set[ProcessListener]':
+        return self._listeners
+
+    def fire_event(self, event_function: Callable[..., Any], *args: Any, **kwargs: Any) -> None:
+        """Call an event method on all listeners.
+
+        :param event_function: the method of the ProcessListener
+        :param args: arguments to pass to the method
+        :param kwargs: keyword arguments to pass to the method
+
+        """
+        if event_function is None:
+            raise ValueError('Must provide valid event method')
+
+        # Make a copy of the list for iteration just in case it changes in a callback
+        for listener in list(self.listeners):
+            try:
+                getattr(listener, event_function.__name__)(*args, **kwargs)
+            except Exception as exception:  # pylint: disable=broad-except
+                _LOGGER.error("Listener '%s' produced an exception:\n%s", listener, exception)

src/plumpy/process_listener.py

@@ -1,14 +1,36 @@
 # -*- coding: utf-8 -*-
 import abc
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING, Any, Dict, Optional
+
+from . import persistence
+from .utils import SAVED_STATE_TYPE, protected
 
 __all__ = ['ProcessListener']
 
 if TYPE_CHECKING:
     from .processes import Process  # pylint: disable=cyclic-import
 
 
-class ProcessListener(metaclass=abc.ABCMeta):
+@persistence.auto_persist('_params')
+class ProcessListener(persistence.Savable, metaclass=abc.ABCMeta):
+
+    # region Persistence methods
+
+    def __init__(self) -> None:
+        super().__init__()
+        self._params: Dict[str, Any] = {}
+
+    def init(self, **kwargs: Any) -> None:
+        self._params = kwargs
+
+    @protected
+    def load_instance_state(
+        self, saved_state: SAVED_STATE_TYPE, load_context: Optional[persistence.LoadSaveContext]
+    ) -> None:
+        super().load_instance_state(saved_state, load_context)
+        self.init(**saved_state['_params'])
+
+    # endregion
 
     def on_process_created(self, process: 'Process') -> None:
         """

src/plumpy/processes.py

@@ -42,6 +42,7 @@
 from .base import state_machine
 from .base.state_machine import StateEntryFailed, StateMachine, TransitionFailed, event
 from .base.utils import call_with_super_check, super_check
+from .event_helper import EventHelper
 from .process_listener import ProcessListener
 from .process_spec import ProcessSpec
 from .utils import PID_TYPE, SAVED_STATE_TYPE, protected
@@ -91,7 +92,9 @@ def func_wrapper(self: Any, *args: Any, **kwargs: Any) -> Any:
     return func_wrapper
 
 
-@persistence.auto_persist('_pid', '_creation_time', '_future', '_paused', '_status', '_pre_paused_status')
+@persistence.auto_persist(
+    '_pid', '_creation_time', '_future', '_paused', '_status', '_pre_paused_status', '_event_helper'
+)
 class Process(StateMachine, persistence.Savable, metaclass=ProcessStateMachineMeta):
     """
     The Process class is the base for any unit of work in plumpy.
@@ -289,7 +292,7 @@ def __init__(
 
         # Runtime variables
         self._future = persistence.SavableFuture(loop=self._loop)
-        self.__event_helper = utils.EventHelper(ProcessListener)
+        self._event_helper = EventHelper(ProcessListener)
         self._logger = logger
         self._communicator = communicator
 
@@ -612,7 +615,7 @@ def load_instance_state(self, saved_state: SAVED_STATE_TYPE, load_context: persi
 
         # Runtime variables, set initial states
         self._future = persistence.SavableFuture()
-        self.__event_helper = utils.EventHelper(ProcessListener)
+        self._event_helper = EventHelper(ProcessListener)
         self._logger = None
         self._communicator = None
 
@@ -661,11 +664,11 @@ def add_process_listener(self, listener: ProcessListener) -> None:
 
         """
         assert (listener != self), 'Cannot listen to yourself!'
-        self.__event_helper.add_listener(listener)
+        self._event_helper.add_listener(listener)
 
     def remove_process_listener(self, listener: ProcessListener) -> None:
         """Remove a process listener from the process."""
-        self.__event_helper.remove_listener(listener)
+        self._event_helper.remove_listener(listener)
 
     @protected
     def set_logger(self, logger: logging.Logger) -> None:
@@ -778,7 +781,7 @@ def on_output_emitting(self, output_port: str, value: Any) -> None:
         """Output is about to be emitted."""
 
     def on_output_emitted(self, output_port: str, value: Any, dynamic: bool) -> None:
-        self.__event_helper.fire_event(ProcessListener.on_output_emitted, self, output_port, value, dynamic)
+        self._event_helper.fire_event(ProcessListener.on_output_emitted, self, output_port, value, dynamic)
 
     @super_check
     def on_wait(self, awaitables: Sequence[Awaitable]) -> None:
@@ -891,7 +894,7 @@ def on_close(self) -> None:
             self._closed = True
 
     def _fire_event(self, evt: Callable[..., Any], *args: Any, **kwargs: Any) -> None:
-        self.__event_helper.fire_event(evt, self, *args, **kwargs)
+        self._event_helper.fire_event(evt, self, *args, **kwargs)
 
     # endregion
 

src/plumpy/utils.py

@@ -27,47 +27,6 @@
 PID_TYPE = Hashable  # pylint: disable=invalid-name
 
 
-class EventHelper:
-
-    def __init__(self, listener_type: 'Type[ProcessListener]'):
-        assert listener_type is not None, 'Must provide valid listener type'
-
-        self._listener_type = listener_type
-        self._listeners: 'Set[ProcessListener]' = set()
-
-    def add_listener(self, listener: 'ProcessListener') -> None:
-        assert isinstance(listener, self._listener_type), 'Listener is not of right type'
-        self._listeners.add(listener)
-
-    def remove_listener(self, listener: 'ProcessListener') -> None:
-        self._listeners.discard(listener)
-
-    def remove_all_listeners(self) -> None:
-        self._listeners.clear()
-
-    @property
-    def listeners(self) -> 'Set[ProcessListener]':
-        return self._listeners
-
-    def fire_event(self, event_function: Callable[..., Any], *args: Any, **kwargs: Any) -> None:
-        """Call an event method on all listeners.
-
-        :param event_function: the method of the ProcessListener
-        :param args: arguments to pass to the method
-        :param kwargs: keyword arguments to pass to the method
-
-        """
-        if event_function is None:
-            raise ValueError('Must provide valid event method')
-
-        # Make a copy of the list for iteration just in case it changes in a callback
-        for listener in list(self.listeners):
-            try:
-                getattr(listener, event_function.__name__)(*args, **kwargs)
-            except Exception as exception:  # pylint: disable=broad-except
-                _LOGGER.error("Listener '%s' produced an exception:\n%s", listener, exception)
-
-
 class Frozendict(Mapping):
     """
     An immutable wrapper around dictionaries that implements the complete :py:class:`collections.abc.Mapping`

test/test_processes.py

@@ -800,7 +800,8 @@ def test_instance_state_with_outputs(self):
             # Check that it is a copy
             self.assertIsNot(outputs, bundle.get(BundleKeys.OUTPUTS, {}))
             # Check the contents are the same
-            self.assertDictEqual(outputs, bundle.get(BundleKeys.OUTPUTS, {}))
+            # Remove the ``ProcessSaver`` instance that is only used for testing
+            utils.compare_dictionaries(None, None, outputs, bundle.get(BundleKeys.OUTPUTS, {}), exclude={'_listeners'})
 
         self.assertIsNot(proc.outputs, saver.snapshots[-1].get(BundleKeys.OUTPUTS, {}))
 
@@ -875,7 +876,7 @@ def _check_round_trip(self, proc1):
         bundle2 = plumpy.Bundle(proc2)
 
         self.assertEqual(proc1.pid, proc2.pid)
-        self.assertDictEqual(bundle1, bundle2)
+        utils.compare_dictionaries(None, None, bundle1, bundle2, exclude={'_listeners'})
 
 
 class TestProcessNamespace(unittest.TestCase):

test/test_workchains.py

@@ -283,6 +283,46 @@ def test_checkpointing(self):
             if step not in ['isA', 's2', 'isB', 's3']:
                 self.assertTrue(finished, f'Step {step} was not called by workflow')
 
+    def test_listener_persistence(self):
+        persister = plumpy.InMemoryPersister()
+        process_finished_count = 0
+
+        class TestListener(plumpy.ProcessListener):
+
+            def on_process_finished(self, process, output):
+                nonlocal process_finished_count
+                process_finished_count += 1
+
+        class SimpleWorkChain(plumpy.WorkChain):
+
+            @classmethod
+            def define(cls, spec):
+                super().define(spec)
+                spec.outline(
+                    cls.step1,
+                    cls.step2,
+                )
+
+            def step1(self):
+                persister.save_checkpoint(self, 'step1')
+
+            def step2(self):
+                persister.save_checkpoint(self, 'step2')
+
+        # add SimpleWorkChain and TestListener to this module global namespace, so they can be reloaded from checkpoint
+        globals()['SimpleWorkChain'] = SimpleWorkChain
+        globals()['TestListener'] = TestListener
+
+        workchain = SimpleWorkChain()
+        workchain.add_process_listener(TestListener())
+        output = workchain.execute()
+
+        self.assertEqual(process_finished_count, 1)
+
+        workchain_checkpoint = persister.load_checkpoint(workchain.pid, 'step1').unbundle()
+        workchain_checkpoint.execute()
+        self.assertEqual(process_finished_count, 2)
+
     def test_return_in_outline(self):
 
         class WcWithReturn(WorkChain):