default reversed, xtrigger argument added

cylc/flow/cfgspec/workflow.py

@@ -785,9 +785,21 @@ def get_script_common_text(this: str, example: Optional[str] = None):
                     :ref:`SequentialTasks`.
             ''')
 
+        Conf('sequential xtriggers default', VDR.V_BOOLEAN, False, desc='''
+            Set to ``True``, this allows for sequential spawning of associated
+            parentless tasks on xtrigger satisfaction.
+            Instead of out to the runahead limit (default: ``False``).
+
+            This workflow wide default can be overridden by a reserved
+            keyword argument in the xtrigger function declaration
+            (``sequential=True/False``).
+
+            The presence of one sequential xtrigger on a parentless task with
+            multiple xtriggers will cause sequential behavior.
+        ''')
         with Conf('xtriggers', desc='''
-                This section is for *External Trigger* function declarations -
-                see :ref:`Section External Triggers`.
+            This section is for *External Trigger* function declarations -
+            see :ref:`Section External Triggers`.
         '''):
             Conf('<xtrigger name>', VDR.V_XTRIGGER, desc='''
                 Any user-defined event trigger function declarations and
@@ -797,26 +809,8 @@ def get_script_common_text(this: str, example: Optional[str] = None):
 
                 Example::
 
-            .. code-block:: cylc
-
-                [[xtriggers]]
-                    my_trig = my_trigger(arg1, arg2, kwarg1, kwarg2):PT10S
-                    [[[settings]]]
-                        non-sequential xtriggers = my_trig
-
+                ``my_trigger(arg1, arg2, kwarg1, kwarg2):PT10S``
             ''')
-            with Conf('settings', desc='''
-                Section heading for xtrigger behavior settings.
-            ''') as Queue:
-                Conf('non-sequential xtriggers', VDR.V_STRING_LIST, desc='''
-                    A list of xtrigger labels whose xtrigger, of associated
-                    parentless task, be checked out to the runahead limit.
-
-                    This allows for non-sequential xtrigger checking.
-
-                    A task with multiple xtriggers requires all labels
-                    be specified to behave in this way.
-                ''')
 
         with Conf('graph', desc=f'''
             The workflow graph is defined under this section.

cylc/flow/config.py

@@ -1760,17 +1760,16 @@ def generate_triggers(self, lexpression, left_nodes, right, seq,
         validator = XtriggerNameValidator.validate
         xtrigs = self.cfg['scheduling']['xtriggers']
         for label in xtrigs:
-            if (
-                label == 'settings'
-                and not isinstance(xtrigs[label], SubFuncContext)
-            ):
-                continue
             valid, msg = validator(label)
             if not valid:
                 raise WorkflowConfigError(
                     f'Invalid xtrigger name "{label}" - {msg}'
                 )
 
+        if self.xtrigger_mgr is not None:
+            self.xtrigger_mgr.sequential_xtriggers_default = (
+                self.cfg['scheduling']['sequential xtriggers default']
+            )
         for label in xtrig_labels:
             try:
                 xtrig = xtrigs[label]
@@ -1802,12 +1801,6 @@ def generate_triggers(self, lexpression, left_nodes, right, seq,
                 self.xtrigger_mgr.add_trig(label, xtrig, self.fdir)
             self.taskdefs[right].add_xtrig_label(label, seq)
 
-        if self.xtrigger_mgr is not None:
-            with suppress(KeyError):
-                self.xtrigger_mgr.non_sequential_labels.update(
-                    set(xtrigs['settings']['non-sequential xtriggers'])
-                )
-
     def get_actual_first_point(self, start_point):
         """Get actual first cycle point for the workflow
 

cylc/flow/task_pool.py

@@ -606,8 +606,8 @@ def load_db_task_pool_for_restart(self, row_idx, row):
             # Set xtrigger checking type, which effects parentless spawning.
             if (
                 itask.tdef.is_parentless(itask.point)
-                and set(itask.state.xtriggers.keys()).difference(
-                    self.xtrigger_mgr.non_sequential_labels
+                and set(itask.state.xtriggers.keys()).intersection(
+                    self.xtrigger_mgr.sequential_xtrigger_labels
                 )
             ):
                 itask.is_xtrigger_sequential = True
@@ -748,8 +748,8 @@ def _get_spawned_or_merged_task(
             # if the task was found set xtrigger checking type.
             if (
                 ntask is not None
-                and set(ntask.state.xtriggers.keys()).difference(
-                    self.xtrigger_mgr.non_sequential_labels
+                and set(ntask.state.xtriggers.keys()).intersection(
+                    self.xtrigger_mgr.sequential_xtrigger_labels
                 )
             ):
                 ntask.is_xtrigger_sequential = True

cylc/flow/unicode_rules.py

@@ -323,7 +323,6 @@ class XtriggerNameValidator(UnicodeRuleChecker):
     RULES = [
         allowed_characters(r'a-zA-Z0-9', '_'),
         not_starts_with('_cylc'),
-        not_equals('settings'),
     ]
 
 

cylc/flow/xtrigger_mgr.py

@@ -16,6 +16,7 @@
 
 from contextlib import suppress
 from enum import Enum
+from inspect import getfullargspec
 import json
 import re
 from copy import deepcopy
@@ -182,6 +183,32 @@ class XtriggerManager:
     managed uniquely - i.e. many tasks depending on the same clock trigger
     (with same offset from cycle point) get satisfied by the same call.
 
+    Parentless tasks with xtrigger(s) are, by default, spawned out to the
+    runahead limit. This results in non-sequential, and potentially
+    unnecessary, checking out to this limit (and may introduce clutter to
+    user interfaces). An option to make this sequential is now available,
+    by changing the default for all xtriggers in a workflow, and a way to
+    override this default with a (reserved) keyword function argument
+    (i.e. "sequential=True/False"):
+
+    # Example:
+    [scheduling]
+        sequential xtrigger default = True
+        [[xtriggers]]
+            clock_0 = wall_clock()  # offset PT0H
+            clock_1 = wall_clock(offset=PT1H)
+                 # or wall_clock(PT1H)
+            workflow_x = workflow_state(
+                workflow=other,
+                point=%(task_cycle_point)s,
+                sequential=False
+            ):PT30S
+        [[graph]]
+            PT1H = '''
+                @clock_1 & @workflow_x => foo & bar
+                @wall_clock = baz  # pre-defined zero-offset clock
+            '''
+
     Args:
         workflow: workflow name
         user: workflow owner
@@ -213,8 +240,11 @@ def __init__(
 
         # Clock labels, to avoid repeated string comparisons
         self.wall_clock_labels: set = set()
+
+        # Workflow wide default, used when not specified in xtrigger kwargs.
+        self.sequential_xtriggers_default = False
         # Labels whose xtrigger will be checked out to the RH limit.
-        self.non_sequential_labels: set = set()
+        self.sequential_xtrigger_labels: set = set()
         # Gather parentless tasks whose xtrigger(s) have been satisfied
         # (these will be used to spawn the next occurance).
         self.sequential_spawn_next: set = set()
@@ -255,6 +285,7 @@ def validate_xtrigger(label: str, fctx: SubFuncContext, fdir: str) -> None:
                 * If the function module was not found.
                 * If the function was not found in the xtrigger module.
                 * If the function is not callable.
+                * If the function is not callable.
                 * If any string template in the function context
                   arguments are not present in the expected template values.
 
@@ -280,6 +311,15 @@ def validate_xtrigger(label: str, fctx: SubFuncContext, fdir: str) -> None:
                 fname,
                 f"'{fname}' not callable in xtrigger module '{fname}'",
             )
+        if 'sequential' in getfullargspec(func).args:
+            raise XtriggerConfigError(
+                label,
+                fname,
+                (
+                    f"xtrigger module '{fname}' contains reserved"
+                    " argument name 'sequential'"
+                ),
+            )
 
         # Check any string templates in the function arg values (note this
         # won't catch bad task-specific values - which are added dynamically).
@@ -324,6 +364,11 @@ def add_trig(self, label: str, fctx: SubFuncContext, fdir: str) -> None:
         """
         self.validate_xtrigger(label, fctx, fdir)
         self.functx_map[label] = fctx
+        if fctx.func_kwargs.pop(
+            'sequential',
+            self.sequential_xtriggers_default
+        ):
+            self.sequential_xtrigger_labels.add(label)
         if fctx.func_name == "wall_clock":
             self.wall_clock_labels.add(label)
 
@@ -434,11 +479,11 @@ def call_xtriggers_async(self, itask: TaskProxy):
                 # Special case: quick synchronous clock check.
                 if wall_clock(*ctx.func_args, **ctx.func_kwargs):
                     itask.state.xtriggers[label] = True
-                    if itask.is_xtrigger_sequential:
-                        self.sequential_spawn_next.add(itask.identity)
                     self.sat_xtrig[sig] = {}
                     self.data_store_mgr.delta_task_xtrigger(sig, True)
                     LOG.info('xtrigger satisfied: %s = %s', label, sig)
+                    if itask.is_xtrigger_sequential:
+                        self.sequential_spawn_next.add(itask.identity)
                 continue
             # General case: potentially slow asynchronous function call.
             if sig in self.sat_xtrig:

tests/functional/cylc-config/00-simple/section1.stdout

@@ -6,6 +6,7 @@ hold after cycle point =
 stop after cycle point = 
 cycling mode = integer
 runahead limit = P4
+sequential xtriggers default = False
 [[queues]]
     [[[default]]]
         limit = 100
@@ -16,7 +17,5 @@ runahead limit = P4
     clock-expire = 
     sequential = 
 [[xtriggers]]
-    [[[settings]]]
-        non-sequential xtriggers = 
 [[graph]]
     R1 = OPS:finish-all => VAR