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