Avoid inf recursion in BroadcastReceiver.receive()
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BroadcastReceiver.receive()
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This was referenced Jan 10, 2023
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Driven by a bug found in `piker` where we'd get an inf recursion error due to `BroadcastReceiver.receive()` being called when consumer tasks are awoken but no value is ready to `.nowait_receive()`. This new rework takes an approach closer to the interface and internals of `trio.MemoryReceiveChannel` particularly in terms of, - implementing a `BroadcastReceiver.receive_nowait()` and using it within the async `.receive()`. - failing over to an internal `._receive_from_underlying()` when the `_nowait()` call raises `trio.WouldBlock`. - adding `BroadcastState.statistics()` for debugging and testing dropping recursion from `.receive()`.
Since one-way streaming can be accomplished by just *not* sending on one side (and/or thus wrapping such usage in a more restrictive API), we just drop the recv-only parent type. The only method different was `MsgStream.send()`, now merged in. Further in usage of `.subscribe()` we monkey patch the underlying stream's `.send()` onto the delivered broadcast receiver so that subscriber tasks can two-way stream as though using the stream directly. This allows us to more definitively drop `tractor.open_stream_from()` in the longer run if we so choose as well; note currently this will potentially create an issue if a caller tries to `.send()` on such a one way stream.
Makes the broadcast test suite not hang xD, and is our expected default behaviour. Also removes a ton of commented legacy cruft from before the refactor to remove the `.receive()` recursion and fixes some typing. Oh right, and in the case where there's only one subscriber left we warn log about it since in theory we could actually entirely unwind the bcaster back to the original underlying, though not sure if that's sane or works for some use cases (like wanting to have some other subscriber get added dynamically later).
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guilledk
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Jan 30, 2023
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Originally driven by a bug found in
pikerwhere we'd get an inf recursion error due toBroadcastReceiver.receive()being recursively called when consumer tasks are awoken but no value is ready tonowaitreceive.trio.MemoryReceiveChannelparticularly in terms of,BroadcastReceiver.receive_nowait()and using it within the async.receive()._receive_from_underlying()when the_nowait()call raisestrio.WouldBlockBroadcastState.statistics()for debugging and testing.receive()BroadcastReceiver._raise_on_lag: boolwhich can be set to avoidLaggederrors from being raised in the case where a user knows they want/need a cheap or nasty patternMsgStreamas only stream type!MsgStreamandReceiveMsgStreammerging the two types into the former; the only thing differing was.send()which should really be a choice not to use since (at least eventually) the underlying impl will always be a bidir stream.BroadcastRecieverdelivered fromMsgStream.subscribe()with a.send()which delegates to the underlying stream making it very simple to support multi-task usage of any fan-out stream 🏄🏼TODO:
ipythonWIP commit (aac8d34) from this historyhopefully a (set of) test(s) to demonstrate the original recursion error?=> don't think it's worth it, if it shows up again then yes..