eventloop: fix timer reentrancy

Avoid running multiple callbacks if a timer is stopped and restarted
in quick succession.

Signed-off-by:  Eric Callahan <arksine.code@gmail.com>

moonraker/eventloop.py

@@ -164,12 +164,18 @@ class FlexTimer:
         self.eventloop = eventloop
         self.callback = callback
         self.timer_handle: Optional[asyncio.TimerHandle] = None
+        self.timer_task: Optional[asyncio.Task] = None
         self.running: bool = False
 
+    def in_callback(self) -> bool:
+        return self.timer_task is not None and not self.timer_task.done()
+
     def start(self, delay: float = 0.):
         if self.running:
             return
         self.running = True
+        if self.in_callback():
+            return
         call_time = self.eventloop.get_loop_time() + delay
         self.timer_handle = self.eventloop.call_at(
             call_time, self._schedule_task)
@@ -182,9 +188,14 @@ class FlexTimer:
             self.timer_handle.cancel()
             self.timer_handle = None
 
+    async def wait_timer_done(self) -> None:
+        if self.timer_task is None:
+            return
+        await self.timer_task
+
     def _schedule_task(self):
         self.timer_handle = None
-        self.eventloop.create_task(self._call_wrapper())
+        self.timer_task = self.eventloop.create_task(self._call_wrapper())
 
     def is_running(self) -> bool:
         return self.running
@@ -192,8 +203,14 @@ class FlexTimer:
     async def _call_wrapper(self):
         if not self.running:
             return
+        try:
             ret = self.callback(self.eventloop.get_loop_time())
             if isinstance(ret, Awaitable):
                 ret = await ret
+        except Exception:
+            self.running = False
+            raise
+        finally:
+            self.timer_task = None
         if self.running:
             self.timer_handle = self.eventloop.call_at(ret, self._schedule_task)