Log exceptions in failed scan tasks (#282)

Author: GDYendell

src/fastcs/attributes/attr_r.py

@@ -110,8 +110,8 @@ async def update_attribute():
             try:
                 self.log_event("Update attribute", topic=self)
                 await update_callback(self)
-            except Exception as e:
-                logger.opt(exception=e).error("Update loop failed", attribute=self)
+            except Exception:
+                logger.error("Attribute update loop stopped", attribute=self)
                 raise
 
         return update_attribute

src/fastcs/attributes/attr_w.py

@@ -68,6 +68,8 @@ async def put(self, setpoint: DType_T, sync_setpoint: bool = False) -> None:
                     "Sync setpoint failed", attribute=self, setpoint=setpoint
                 )
 
+        self.log_event("Put complete", setpoint=setpoint, attribute=self)
+
     async def _call_sync_setpoint_callbacks(self, setpoint: DType_T) -> None:
         if self._sync_setpoint_callbacks:
             await asyncio.gather(

src/fastcs/control_system.py

@@ -7,7 +7,6 @@
 from IPython.terminal.embed import InteractiveShellEmbed
 
 from fastcs.controllers import BaseController, Controller
-from fastcs.exceptions import FastCSError
 from fastcs.logging import bind_logger
 from fastcs.methods import Command, Scan, ScanCallback
 from fastcs.tracer import Tracer
@@ -63,11 +62,8 @@ async def _start_scan_tasks(self):
     def _scan_done(self, task: asyncio.Task):
         try:
             task.result()
-        except Exception as e:
-            raise FastCSError(
-                "Exception raised in scan method of "
-                f"{self._controller.__class__.__name__}"
-            ) from e
+        except Exception:
+            logger.exception("Exception raised in scan task")
 
     def _stop_scan_tasks(self):
         for task in self._scan_tasks:

src/fastcs/methods/scan.py

@@ -2,8 +2,11 @@
 from types import MethodType
 
 from fastcs.controllers import BaseController
+from fastcs.logging import bind_logger
 from fastcs.methods.method import Controller_T, Method
 
+logger = bind_logger(logger_name=__name__)
+
 UnboundScanCallback = Callable[[Controller_T], Coroutine[None, None, None]]
 """A Scan callback that is unbound and must be called with a `Controller` instance"""
 ScanCallback = Callable[[], Coroutine[None, None, None]]
@@ -36,6 +39,17 @@ def _validate(self, fn: ScanCallback) -> None:
     async def __call__(self):
         return await self._fn()
 
+    @property
+    def fn(self):
+        async def scan():
+            try:
+                return await self._fn()
+            except Exception:
+                logger.error("Scan update loop stopped", fn=self._fn)
+                raise
+
+        return scan
+
 
 class UnboundScan(Method[Controller_T]):
     """A wrapper of an unbound `Controller` method to be bound into a `Scan`.

tests/test_control_system.py

@@ -7,7 +7,6 @@
 from fastcs.control_system import FastCS, build_controller_api
 from fastcs.controllers import Controller
 from fastcs.datatypes import Int
-from fastcs.exceptions import FastCSError
 from fastcs.methods import Command, command, scan
 from fastcs.util import ONCE
 
@@ -152,8 +151,6 @@ async def raise_exception(self):
     task = asyncio.create_task(fastcs.serve(interactive=False))
     # This allows scan time to run
     await asyncio.sleep(0.2)
-    # _scan_done should raise an exception
-    assert isinstance(exception_info["exception"], FastCSError)
     for task in fastcs._scan_tasks:
         internal_exception = task.exception()
         assert internal_exception