AsyncServiceBrowser must recheck for handlers to call when holding condition (#483)

bdraco · web-flow · commit 960693628006 · 2021-06-06T14:14:17.000-10:00
- There was a short race condition window where the AsyncServiceBrowser
  could add to _handlers_to_call in the Engine thread, have the
  condition notify_all called, but since the AsyncServiceBrowser was
  not yet holding the condition it would not know to stop waiting
  and process the handlers to call.
diff --git a/zeroconf/asyncio.py b/zeroconf/asyncio.py
@@ -209,12 +209,15 @@ async def async_run(self) -> None:
         """Run the browser task."""
         self.run()
         while True:
-            if not self._handlers_to_call:
-                # Wait for the type has the smallest next time
-                next_time = min(self._next_time.values())
-                now = current_time_millis()
-                if next_time > now:
-                    await self.aiozc.async_wait(next_time - now)
+            timeout = self._seconds_to_wait()
+            if timeout:
+                async with self.aiozc.condition:
+                    # We must check again while holding the condition
+                    # in case the other thread has added to _handlers_to_call
+                    # between when we checked above when we were not
+                    # holding the condition
+                    if not self._handlers_to_call:
+                        await wait_condition_or_timeout(self.aiozc.condition, timeout)
 
             out = self.generate_ready_queries()
             if out:
