[FIX] bus: gc event at the end of a polling

When making a poll, an event is registered on each channel. Once
a notification is sent on a channel, only the events of the
notified channel are removed. A pointer to the event is kept
in all other channel the user subscribes to until those channel
are notified.

Since a user usually has many mail.channels but only a few active ones,
a new event and a bunch of pointers are created at each poll and
never removed.

This fix simply remove the pointers to the current event at the
end of a poll.

closes odoo/odoo#31215

Signed-off-by: Toufik Benjaa (tbe) <tbe@odoo.com>

addons/bus/models/bus.py

@@ -141,7 +141,7 @@ class ImDispatch(object):
 
             event = self.Event()
             for channel in channels:
-                self.channels.setdefault(hashable(channel), []).append(event)
+                self.channels.setdefault(hashable(channel), set()).add(event)
             try:
                 event.wait(timeout=timeout)
                 with registry.cursor() as cr:
@@ -150,6 +150,12 @@ class ImDispatch(object):
             except Exception:
                 # timeout
                 pass
+            finally:
+                # gc pointers to event
+                for channel in channels:
+                    channel_events = self.channels.get(hashable(channel))
+                    if channel_events and event in channel_events:
+                        channel_events.remove(event)
         return notifications
 
     def loop(self):
@@ -170,7 +176,7 @@ class ImDispatch(object):
                     # dispatch to local threads/greenlets
                     events = set()
                     for channel in channels:
-                        events.update(self.channels.pop(hashable(channel), []))
+                        events.update(self.channels.pop(hashable(channel), set()))
                     for event in events:
                         event.set()