better shutdown on crash about ijulia.jl HOT 6 CLOSED

Since IPython ignores the crash message, how should we tell it we've shut down?

For real shutdown there is a shutdown request and reply. In case of real full kernel crash, the heartbeat will fail and the frontend is responsible to ask for ask restart (automatic in case of notebook, prompt user for qtconsole)

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@Carreau, I understand that the heartbeat stop will cause a restart. However, it would be nice have a mechanism to report the reason for the crash to the front-end if possible (obviously not possible for a segfault or similar catastrophic error, but we can certainly do it in cases like uncaught exceptions).

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Shouldn't one just catch all exceptions and report them as errors? Are there situations where we can send a message back but can't continue operating? That seems like a strange intermediate situation.

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Sure, that's one possibility, just send a pyerr message back to the frontend and continue operating. But we may want some mechanism to exit if we get into an infinite loop of exceptions this way.

(For now I want to crash on an unhandled exception just to make sure that we don't accidentally ignore it.)

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The above patch changes the behavior so that it tries to continue on an unexpected exception. However, sending a pyerr message doesn't seem to work, perhaps because I'm just sending a new UUID as the session parameter (since this is not in the middle of an execute_request). @minrk or @Carreau, is there a way to send a pyerr (or similar) message outside of the context of an execute_request, to report to the front ends that something may be going wrong in the kernel?

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IURC, the "session" UUID should change only once every kernel restart, it should stay the same across messages.

The only problem is that in between execute request if you publish a message with a message id that no frontend know of, the frontend will just ignore it.

I guess you could try to keep track of last seen session-id and message id by peeking into the messages.

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