Simplify and fix runahead computation. (cylc#5893)

## Simplify and fix runahead computation.

* In back-compat mode the cycle point time zone is assumed to be local, whereas in normal mode it is assumed to be UTC. There was contamination of the point parse caching where the time zone would carry over from tests of back-compat vs normal mode

### Testing
* New runhead integration test.
* Reload: test reloading doesn't nudge the runahead limit
* We were using the pytest-env plugin to run the tests in a non-UTC time zone: The pytest-env plugin doesn't work with pytest-xdist so this was being ignored.
* Add both runahead formats to existing tests for compute runahead. Add compat mode and not compat mode versions of the future triggers bug test.
* Wrote a test to check for changes of runahead limit based on changing task statuses in compat mode.

---------

Co-authored-by: Oliver Sanders <[email protected]>
Co-authored-by: Ronnie Dutta <[email protected]>
Co-authored-by: Tim Pillinger <[email protected]>

.github/workflows/test_fast.yml

@@ -20,11 +20,17 @@ jobs:
       fail-fast: false # Don't let a failed MacOS run stop the Ubuntu runs
       matrix:
         os: ['ubuntu-latest']
-        python-version: ['3.7', '3.8', '3.9', '3.10', '3.11']
+        python-version: ['3.7', '3.8', '3.10', '3.11']
         include:
+          # mac os test
           - os: 'macos-11'
-            python-version: '3.7'
+            python-version: '3.7'  # oldest supported version
+          # non-utc timezone test
+          - os: 'ubuntu-latest'
+            python-version: '3.9'  # not the oldest, not the most recent version
+            time-zone: 'XXX-09:35'
     env:
+      TZ: ${{ matrix.time-zone }}
       PYTEST_ADDOPTS: --cov --cov-append -n 5 --color=yes
     steps:
       - name: Checkout

changes.d/5893.fix

@@ -0,0 +1 @@
+Fixed bug in computing a time interval-based runahead limit when future triggers are present.

cylc/flow/cycling/__init__.py

@@ -415,22 +415,6 @@ def get_stop_point(self):
         """Return the last point of this sequence, or None if unbounded."""
         pass
 
-    def get_first_n_points(self, n, point=None):
-        """Return a list of first n points of this sequence."""
-        if point is None:
-            p1 = self.get_start_point()
-        else:
-            p1 = self.get_first_point(point)
-        if p1 is None:
-            return []
-        result = [p1]
-        for _ in range(1, n):
-            p1 = self.get_next_point_on_sequence(p1)
-            if p1 is None:
-                break
-            result.append(p1)
-        return result
-
     @abstractmethod
     def __eq__(self, other) -> bool:
         # Return True if other (sequence) is equal to self.

cylc/flow/cycling/iso8601.py

@@ -943,12 +943,22 @@ def _interval_parse(interval_string):
 
 def point_parse(point_string: str) -> 'TimePoint':
     """Parse a point_string into a proper TimePoint object."""
-    return _point_parse(point_string, WorkflowSpecifics.DUMP_FORMAT)
+    return _point_parse(
+        point_string,
+        WorkflowSpecifics.DUMP_FORMAT,
+        WorkflowSpecifics.ASSUMED_TIME_ZONE
+    )
 
 
 @lru_cache(10000)
-def _point_parse(point_string, _dump_fmt):
-    """Parse a point_string into a proper TimePoint object."""
+def _point_parse(point_string: str, _dump_fmt, _tz) -> 'TimePoint':
+    """Parse a point_string into a proper TimePoint object.
+
+    Args:
+        point_string: The string to parse.
+        _dump_fmt: Dump format (only used to avoid invalid cache hits).
+        _tz: Cycle point time zone (only used to avoid invalid cache hits).
+    """
     if "%" in WorkflowSpecifics.DUMP_FORMAT:
         # May be a custom not-quite ISO 8601 dump format.
         with contextlib.suppress(IsodatetimeError):

cylc/flow/task_pool.py

@@ -309,82 +309,48 @@ def compute_runahead(self, force=False) -> bool:
 
         With force=True we recompute the limit even if the base point has not
         changed (needed if max_future_offset changed, or on reload).
-        """
 
+        """
         limit = self.config.runahead_limit  # e.g. P2 or P2D
         count_cycles = False
         with suppress(TypeError):
             # Count cycles (integer cycling, and optional for datetime too).
             ilimit = int(limit)  # type: ignore
             count_cycles = True
 
-        base_point: 'PointBase'
-        points: List['PointBase'] = []
+        base_point: Optional['PointBase'] = None
 
+        # First get the runahead base point.
         if not self.main_pool:
-            # No tasks yet, just consider sequence points.
-            if count_cycles:
-                # Get the first ilimit points in each sequence.
-                # (After workflow start point - sequence may begin earlier).
-                points = [
-                    point
-                    for plist in [
-                        seq.get_first_n_points(
-                            ilimit, self.config.start_point)
-                        for seq in self.config.sequences
-                    ]
-                    for point in plist
-                ]
-                # Drop points beyond the limit.
-                points = sorted(points)[:ilimit + 1]
-                base_point = min(points)
-
-            else:
-                # Start at first point in each sequence.
-                # (After workflow start point - sequence may begin earlier).
-                points = [
-                    point
-                    for point in {
-                        seq.get_first_point(self.config.start_point)
-                        for seq in self.config.sequences
-                    }
-                    if point is not None
-                ]
-                base_point = min(points)
-                # Drop points beyond the limit.
-                points = [
-                    point
-                    for point in points
-                    if point <= base_point + limit
-                ]
-
+            # Find the earliest sequence point beyond the workflow start point.
+            base_point = min(
+                point
+                for point in {
+                    seq.get_first_point(self.config.start_point)
+                    for seq in self.config.sequences
+                }
+                if point is not None
+            )
         else:
-            # Find the earliest point with unfinished tasks.
+            # Find the earliest point with incomplete tasks.
             for point, itasks in sorted(self.get_tasks_by_point().items()):
+                # All n=0 tasks are incomplete by definition, but Cylc 7
+                # ignores failed ones (it does not ignore submit-failed!).
                 if (
-                    points  # got the limit already so this point too
-                    or any(
-                        not itask.state(
-                            TASK_STATUS_FAILED,
-                            TASK_STATUS_SUCCEEDED,
-                            TASK_STATUS_EXPIRED
-                        )
-                        or (
-                            # For Cylc 7 back-compat, ignore incomplete tasks.
-                            # (Success is required in back-compat mode, so
-                            # failedtasks end up as incomplete; and Cylc 7
-                            # ignores failed tasks in computing the limit).
-                            itask.state.outputs.is_incomplete()
-                            and not cylc.flow.flags.cylc7_back_compat
-                        )
+                    cylc.flow.flags.cylc7_back_compat and
+                    all(
+                        itask.state(TASK_STATUS_FAILED)
                         for itask in itasks
                     )
                 ):
-                    points.append(point)
+                    continue
+                base_point = point
+                break
 
-            if not points:
-                return False
-            base_point = min(points)
+        if base_point is None:
+            return False
+
+        LOG.debug(f"Runahead: base point {base_point}")
 
         if self._prev_runahead_base_point is None:
             self._prev_runahead_base_point = base_point
@@ -401,8 +367,10 @@ def compute_runahead(self, force=False) -> bool:
             # change or the runahead limit is already at stop point.
             return False
 
-        # Get all cycle points possible after the base point.
-        sequence_points: Set['PointBase']
+        # Now generate all possible cycle points from the base point and stop
+        # at the runahead limit point. Note both cycle count and time interval
+        # limits involve all possible cycles, not just active cycles.
+        sequence_points: Set['PointBase'] = set()
         if (
             not force
             and self._prev_runahead_sequence_points
@@ -412,44 +380,48 @@ def compute_runahead(self, force=False) -> bool:
             sequence_points = self._prev_runahead_sequence_points
         else:
             # Recompute possible points.
-            sequence_points = set()
             for sequence in self.config.sequences:
-                seq_point = sequence.get_next_point(base_point)
+                seq_point = sequence.get_first_point(base_point)
                 count = 1
                 while seq_point is not None:
                     if count_cycles:
                         # P0 allows only the base cycle point to run.
                         if count > 1 + ilimit:
+                            # this point may be beyond the runahead limit
                             break
                     else:
                         # PT0H allows only the base cycle point to run.
                         if seq_point > base_point + limit:
+                            # this point can not be beyond the runahead limit
                             break
                     count += 1
                     sequence_points.add(seq_point)
                     seq_point = sequence.get_next_point(seq_point)
             self._prev_runahead_sequence_points = sequence_points
             self._prev_runahead_base_point = base_point
 
-        points = set(points).union(sequence_points)
-
         if count_cycles:
-            # Some sequences may have different intervals.
-            limit_point = sorted(points)[:(ilimit + 1)][-1]
+            # (len(list) may be less than ilimit due to sequence end)
+            limit_point = sorted(sequence_points)[:ilimit + 1][-1]
         else:
-            # We already stopped at the runahead limit.
-            limit_point = sorted(points)[-1]
+            limit_point = max(sequence_points)
 
-        # Adjust for future offset and stop point, if necessary.
+        # Adjust for future offset and stop point.
         pre_adj_limit = limit_point
         if self.max_future_offset is not None:
             limit_point += self.max_future_offset
-            LOG.debug(f"{pre_adj_limit} -> {limit_point} (future offset)")
+            LOG.debug(
+                "Runahead (future trigger adjust):"
+                f" {pre_adj_limit} -> {limit_point}"
+            )
         if self.stop_point and limit_point > self.stop_point:
             limit_point = self.stop_point
-            LOG.debug(f"{pre_adj_limit} -> {limit_point} (stop point)")
-        LOG.debug(f"Runahead limit: {limit_point}")
+            LOG.debug(
+                "Runahead (stop point adjust):"
+                f" {pre_adj_limit} -> {limit_point} (stop point)"
+            )
 
+        LOG.debug(f"Runahead limit: {limit_point}")
         self.runahead_limit_point = limit_point
         return True
 

pytest.ini

@@ -32,13 +32,10 @@ testpaths =
     cylc/flow/
     tests/unit/
     tests/integration/
-env =
-    # a weird timezone to check that tests aren't assuming the local timezone
-    TZ=XXX-09:35
 doctest_optionflags =
     NORMALIZE_WHITESPACE
     IGNORE_EXCEPTION_DETAIL
     ELLIPSIS
 asyncio_mode = auto
 markers=
-    linkcheck: Test links
+    linkcheck: Test links

setup.cfg

@@ -119,7 +119,6 @@ tests =
     pytest-asyncio>=0.17,!=0.23.*
     pytest-cov>=2.8.0
     pytest-xdist>=2
-    pytest-env>=0.6.2
     pytest>=6
     testfixtures>=6.11.0
     towncrier>=23