allow restarting after an error

- fix #272
- JournalSequenceError was raised if there was any incomplete stage, even if the stage that you are trying to start is the incomplete one
- add tests for mdpow.restart
- clarified docs for Journal and Journalled

CHANGES

@@ -68,6 +68,7 @@ Fixes
 * fix rcoulomb in CHARMM energy minimization MDP template file (PR #210)
 * fix ensemble.EnsembleAnalysis.check_groups_from_common_ensemble (#212)
 * updated versioneer (#285)
+* fix that simulation stages cannot be restarted after error (#272)
 
 
 2022-01-03    0.8.0

mdpow/restart.py

@@ -116,7 +116,7 @@ def incomplete(self):
     def incomplete(self, stage):
         if not stage in self.stages:
             raise ValueError(
-                "can only assign a registered stage from %(stages)r" % vars(self)
+                "Can only assign a registered stage from %(stages)r" % vars(self)
             )
         self.__incomplete = stage
 
@@ -157,7 +157,16 @@ def has_completed(self, stage):
         return stage in self.history
 
     def has_not_completed(self, stage):
-        """Returns ``True`` if the *stage* had been started but not completed yet."""
+        """Returns ``True`` if the *stage* had been started but not completed yet.
+
+        This is subtly different from ``not`` :func:`has_completed` in
+        that two things have to be true:
+
+        1. No stage is active (which is the case when a restart is attempted).
+        2. The `stage` has not been completed previously (i.e.,
+           :func:`has_completed` returns ``False``)
+
+        """
         return self.current is None and not self.has_completed(stage)
 
     def clear(self):
@@ -190,13 +199,14 @@ def __init__(self, *args, **kwargs):
             len(self.journal.history)
         except AttributeError:
             self.journal = Journal(self.protocols)
-        super(Journalled, self).__init__(*args, **kwargs)
+        super().__init__(*args, **kwargs)
 
     def get_protocol(self, protocol):
         """Return method for *protocol*.
 
         - If *protocol* is a real method of the class then the method is
-          returned.
+          returned. This method should implement its own use of
+          :meth:`Journal.start` and :meth:`Journal.completed`.
 
         - If *protocol* is a registered protocol name but no method of
           the name exists (i.e. *protocol* is a "dummy protocol") then
@@ -205,9 +215,12 @@ def get_protocol(self, protocol):
 
           .. function:: dummy_protocol(func, *args, **kwargs)
 
-             Runs *func* with the arguments and keywords between calls
-             to :meth:`Journal.start` and :meth:`Journal.completed`,
-             with the stage set to *protocol*.
+             Runs *func* with the arguments and keywords between calls to
+             :meth:`Journal.start` and :meth:`Journal.completed`, with the
+             stage set to *protocol*.
+
+             The function should return ``True`` on success and ``False`` on
+             failure.
 
         - Raises a :exc:`ValueError` if the *protocol* is not
           registered (i.e. not found in :attr:`Journalled.protocols`).

mdpow/tests/test_journals.py

@@ -0,0 +1,175 @@
+import pytest
+
+from mdpow import restart
+
+@pytest.fixture
+def journal():
+    return restart.Journal(['pre', 'main', 'post'])
+
+
+class TestJournal:
+    def test_full_sequence(self, journal):
+        journal.start("pre")
+        assert journal.current == "pre"
+        journal.completed("pre")
+
+        journal.start("main")
+        assert journal.current == "main"
+        journal.completed("main")
+
+        journal.start("post")
+        assert journal.current == "post"
+        journal.completed("post")
+
+    def test_set_wrong_stage_ValueError(self, journal):
+        with pytest.raises(ValueError, match="Can only assign a registered stage"):
+            journal.start("BEGIN !")
+
+    def test_JournalSequenceError_no_completion(self, journal):
+        with pytest.raises(restart.JournalSequenceError, match="Cannot start stage"):
+            journal.start("pre")
+            assert journal.current == "pre"
+
+            journal.start("main")
+
+    @pytest.mark.xfail
+    def test_JournalSequenceError_skip_stage(self, journal):
+        # Currently allows skipping a stage and does not enforce ALL previous
+        # stages to have completed.
+        with pytest.raises(restart.JournalSequenceError, match="Cannot start stage"):
+            journal.start("pre")
+            assert journal.current == "pre"
+            journal.completed("pre")
+
+            journal.start("post")
+
+    def test_start_idempotent(self, journal):
+        # test that start() can be called multiple time (#278)
+        journal.start("pre")
+        journal.start("pre")
+        assert journal.current == "pre"
+
+    def test_incomplete_known_stage(self, journal):
+        journal.incomplete = "main"
+        assert journal.incomplete == "main"
+
+    def test_incomplete_unknown_stage_ValueError(self, journal):
+        with pytest.raises(ValueError, match="Can only assign a registered stage from"):
+            journal.incomplete = "BEGIN !"
+
+    def test_clear(self, journal):
+        journal.start("pre")
+        journal.completed("pre")
+        journal.start("main")
+        # manually setting incomplete
+        journal.incomplete = journal.current
+
+        assert journal.current == "main"
+        assert journal.incomplete == journal.current
+
+        journal.clear()
+        assert journal.current is None
+        assert journal.incomplete is None
+
+    def test_history(self, journal):
+        journal.start("pre")
+        journal.completed("pre")
+        journal.start("main")
+        journal.completed("main")
+        journal.start("post")
+
+        # completed stages
+        assert journal.history == ["pre", "main"]
+
+    def test_history_del(self, journal):
+        journal.start("pre")
+        journal.completed("pre")
+        journal.start("main")
+        journal.completed("main")
+        assert journal.history
+
+        del journal.history
+        assert journal.history == []
+
+    def test_has_completed(self, journal):
+        journal.start("pre")
+        journal.completed("pre")
+
+        assert journal.has_completed("pre")
+        assert not journal.has_completed("main")
+
+    def test_has_not_completed(self, journal):
+        journal.start("pre")
+        journal.completed("pre")
+        journal.start("main")
+        # simulate crash/restart
+        del journal.current
+
+        assert journal.has_not_completed("main")
+        assert not journal.has_not_completed("pre")
+
+
+# need a real class so that it can be pickled later
+class JournalledMemory(restart.Journalled):
+    # divide is a dummy protocol
+    protocols = ["divide", "multiply"]
+
+    def __init__(self):
+        self.memory = 1
+        super().__init__()
+
+    def multiply(self, x):
+        self.journal.start("multiply")
+        self.memory *= x
+        self.journal.completed("multiply")
+
+
+@pytest.fixture
+def journalled():
+    return JournalledMemory()
+
+
+class TestJournalled:
+    @staticmethod
+    def divide(m, x):
+        return m.memory / x
+
+    def test_get_protocol_of_class(self, journalled):
+        f = journalled.get_protocol("multiply")
+        f(10)
+        assert journalled.memory == 10
+        assert journalled.journal.has_completed("multiply")
+
+    def test_get_protocol_dummy(self, journalled):
+        dummy_protocol = journalled.get_protocol("divide")
+        result = dummy_protocol(self.divide, journalled, 10)
+
+        assert result == 1/10
+        assert journalled.journal.has_completed("divide")
+
+    def test_get_protocol_dummy_incomplete(self, journalled):
+        dummy_protocol = journalled.get_protocol("divide")
+        with pytest.raises(ZeroDivisionError):
+            result = dummy_protocol(self.divide, journalled, 0)
+        assert not journalled.journal.has_completed("divide")
+
+    def test_save_load(self, tmp_path):
+        # instantiate a class that can be pickled (without pytest magic)
+        journalled = JournalledMemory()
+        f = journalled.get_protocol("multiply")
+        f(10)
+        assert journalled.memory == 10
+
+        pickle = tmp_path / "memory.pkl"
+        journalled.save(pickle)
+
+        assert pickle.exists()
+
+        # change instance
+        f(99)
+        assert journalled.memory == 10 * 99
+
+        # reload previous state
+        journalled.load(pickle)
+        assert journalled.memory == 10
+