2.1 KiB
Add cross-actor-task Context oriented error relay, a new stream overrun error-signal StreamOverrun, and support disabling MsgStream backpressure as the default before a stream is opened or by choice of the user.
We added stricter semantics around tractor.Context.open_stream(): particularly to do with streams which are only opened at one end. Previously, if only one end opened a stream there was no way for that sender to know if msgs are being received until first, the feeder mem chan on the receiver side hit a backpressure state and then that condition delayed its msg loop processing task to eventually create backpressure on the associated IPC transport. This is non-ideal in the case where the receiver side never opened a stream by mistake since it results in silent block of the sender and no adherence to the underlying mem chan buffer size settings (which is still unsolved btw).
To solve this we add non-backpressure style message pushing inside Actor._push_result() by default and only use the backpressure trio.MemorySendChannel.send() call iff the local end of the context has entered Context.open_stream():. This way if the stream was never opened but the mem chan is overrun, we relay back to the sender a (new exception) SteamOverrun error which is raised in the sender's scope with a special error message about the stream never having been opened. Further, this behaviour (non-backpressure style where senders can expect an error on overruns) can now be enabled with .open_stream(backpressure=False) and the underlying mem chan size can be specified with a kwarg msg_buffer_size: int.
Further bug fixes and enhancements in this changeset include: - fix a race we were ignoring where if the callee task opened a context it could enter Context.open_stream() before calling .started(). - Disallow calling Context.started() more then once. - Enable Context linked tasks error relaying via the new Context._maybe_raise_from_remote_msg() which (for now) uses a simple trio.Nursery.start_soon() to raise the error via closure in the local scope.