fix(python): route event-group messages sent by the owner actor#303
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richardssam wants to merge 1 commit into
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fix(python): route event-group messages sent by the owner actor#303richardssam wants to merge 1 commit into
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Python event-group subscriptions could silently drop messages. When a C++ event group broadcasts, the CAF sender is the owner actor (e.g. a Playhead, Timeline, or selection actor), not the event-group actor the Python code subscribed to. EventToPythonThreadLockerActor looked up callbacks by sender address, so those messages matched no callback and were never delivered. This affects any subscribe_to_event_group() consumer, not just playheads. For example, a Python plugin subscribing to a timeline's change events or a viewport's current-selection events receives nothing, so it cannot detect or forward structure/selection changes. Reproduced with an external sync plugin: reverting the owner-actor argument makes an xSTUDIO-driven add/select/delete sequence fail to propagate to a peer (our delete_media_xstudio integration test), while it passes with the fix in place. - Track the optional owner actor per callback ID in EventToPythonThreadLockerActor. - Route an incoming message via the owner actor address as a fallback when the sender does not match any event-group key. - Add a broadcast_down_atom handler to purge stale callback entries when a subscribed owner actor dies, preventing a SIGSEGV on timeline switches where the old actor is torn down mid-dispatch. - Update subscribe_to_event_group in module.py to pass the owner actor as the third argument to add_message_callback (backward compatible: the C++ side still accepts the existing 2-arg form). Signed-off-by: Sam.Richards@taurich.org <Sam.Richards@taurich.org> Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Summary
Fixes
EventToPythonThreadLockerActorso messages broadcast by a C++ eventgroup are actually delivered to their Python subscribers, and prevents a
SIGSEGV when a subscribed actor is torn down mid-dispatch.
When a C++ event group broadcasts, the CAF sender is the owner actor
(e.g. a Playhead, Timeline, or selection actor), not the event-group actor the
Python code subscribed to. The dispatcher matched callbacks by sender address,
so those messages hit no callback and were silently dropped.
Why it matters (general, not playhead-specific)
This affects any
subscribe_to_event_group()consumer. Concretely, a Pythonplugin that subscribes to a timeline's change events or a viewport's
current-selection events receives nothing today, so it can't detect or forward
structure/selection changes.
Reproduced end-to-end with an external sync plugin: reverting the owner-actor
argument makes an xSTUDIO-driven add-media / select / delete-media sequence
fail to propagate to a peer (our
delete_media_xstudiointegration test); itpasses with the fix.
Changes
EventToPythonThreadLockerActor.sender matches no event-group key.
broadcast_down_atomhandler to purge stale callback entries when asubscribed owner actor dies (fixes the timeline-switch SIGSEGV).
subscribe_to_event_group(module.py) passes the owner actor as the 3rd argto
add_message_callback— backward compatible; the C++ side still acceptsthe 2-arg form.
Relationship to #270
This supersedes #270, which framed the fix around playhead events — where the
concern was that playhead event payloads carry types not bound to Python. This
version is scoped to the general event-group routing mechanism and is
demonstrated with a non-playhead case (timeline structure / selection sync)
that carries Python-friendly data. The playhead-specific Python plumbing from
#270 is intentionally not included.
Written with assistance from Claude.