Fix failure to shutdown on keyboard interrupt

CHANGES.md

@@ -164,6 +164,10 @@ task outputs/message triggers are now validated.
 workflow in a sub-directory of a run directory (as `cylc scan` would not be
 able to find it).
 
+[#3982](https://github.com/cylc/cylc-flow/pull/3982) - Fix bug preventing
+workflow from shutting down properly on a keyboard interrupt (Ctrl+C) in
+Python 3.8+.
+
 -------------------------------------------------------------------------------
 ## __cylc-8.0a2 (2020-07-03)__
 

cylc/flow/scheduler.py

@@ -611,13 +611,8 @@ async def start_scheduler(self):
             await self.shutdown(exc)
             raise exc from None
 
-        except Exception as exc:
-            try:
-                await self.shutdown(exc)
-            except Exception as exc2:
-                # In case of exceptions in the shutdown method itself
-                LOG.exception(exc2)
-            raise exc from None
+        except (KeyboardInterrupt, asyncio.CancelledError, Exception) as exc:
+            await self.handle_exception(exc)
 
         else:
             # main loop ends (not used?)
@@ -643,9 +638,8 @@ async def run(self):
             await self.configure()
             await self.start_servers()
             await self.log_start()
-        except Exception as exc:
-            await self.shutdown(exc)
-            raise
+        except (KeyboardInterrupt, asyncio.CancelledError, Exception) as exc:
+            await self.handle_exception(exc)
         else:
             # note start_scheduler handles its own shutdown logic
             await self.start_scheduler()
@@ -1619,16 +1613,19 @@ async def shutdown(self, reason):
 
         """
         if isinstance(reason, SchedulerStop):
-            LOG.info('Suite shutting down - %s', reason.args[0])
+            LOG.info(f'Suite shutting down - {reason.args[0]}')
         elif isinstance(reason, SchedulerError):
-            LOG.error('Suite shutting down - %s', reason)
+            LOG.error(f'Suite shutting down - {reason}')
         elif isinstance(reason, SuiteConfigError):
             LOG.error(f'{SuiteConfigError.__name__}: {reason}')
         elif isinstance(reason, PlatformLookupError):
             LOG.error(f'{PlatformLookupError.__name__}: {reason}')
         else:
             LOG.exception(reason)
-            LOG.critical('Suite shutting down - %s', reason)
+            if str(reason):
+                LOG.critical(f'Suite shutting down - {reason}')
+            else:
+                LOG.critical('Suite shutting down')
 
         if self.proc_pool:
             self.proc_pool.close()
@@ -1836,3 +1833,18 @@ def process_cylc_stop_point(self):
         if stoppoint is not None:
             self.options.stopcp = str(stoppoint)
             self.pool.set_stop_point(get_point(self.options.stopcp))
+
+    async def handle_exception(self, exc):
+        """Gracefully shut down the scheduler.
+
+        This re-raises the caught exception, to be caught higher up.
+
+        Args:
+            exc: The caught exception to be logged during the shutdown.
+        """
+        try:
+            await self.shutdown(exc)
+        except Exception as exc2:
+            # In case of exceptions in the shutdown method itself
+            LOG.exception(exc2)
+        raise exc from None

cylc/flow/scheduler_cli.py

@@ -406,13 +406,7 @@ async def _run(parser, options, reg, is_restart, scheduler):
     # stop cylc stop
     except SchedulerError:
         ret = 1
-    except KeyboardInterrupt as exc:
-        try:
-            await scheduler.shutdown(exc)
-        except Exception as exc2:
-            # In case of exceptions in the shutdown method itself.
-            LOG.exception(exc2)
-            raise exc2 from None
+    except (KeyboardInterrupt, asyncio.CancelledError):
         ret = 2
     except Exception:
         ret = 3