Update session_exists() to account for invalid sessions due to culling #4219
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When kernels are culled, the kernel is terminated in the background, unbeknownst to the session management. As a result, invalid sessions can be produced that appear to exist, yet cannot produce a model from the persisted row due to the associated kernel no longer being active. Prior to this change, these sessions, when encountered via a subsequent call to `get_session()`, would be deleted and a KeyError would be raised. This change updates the existence check to tolerate those kinds of sessions. It removes such sessions (as would happen previously), but rather than raise a KeyError when attempting to convert the row to a dictionary, it logs a warning and returns None, which then allows `session_exists()` to return False since the session was removed (as was ultimately the case previously). Calls to `get_session()` remain just as before and have the potential to raise `KeyError` in such cases. The difference now being that the `KeyError` is accompanied by a message indicating the cause. Fixes jupyter#4209
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This was referenced Sep 24, 2019
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When kernels are culled, the kernel is terminated in the background,
unbeknownst to the session management. As a result, invalid sessions
can be produced that appear to exist, yet cannot produce a model from
the persisted row due to the associated kernel no longer being active.
Prior to this change, these sessions, when encountered via a subsequent
call to
get_session(), would be deleted and a KeyError would be raised.This change updates the existence check to tolerate those kinds of sessions.
It removes such sessions (as would happen previously), but rather than
raise a KeyError when attempting to convert the row to a dictionary,
it logs a warning and returns None, which then allows
session_exists()to return False since the session was removed (as was ultimately the
case previously).
Calls to
get_session()remain just as before and have the potentialto raise
KeyErrorin such cases. The difference now being that theKeyErroris accompanied by a message indicating the cause.Fixes #4209