There are two problems with the scheduler engine today. Both relate to
listeners that throw.
The first problem is that any triggered listener that throws a plain old
exception will cause no additional listeners to be triggered for the
event, and will also cause the scheduler to never be invoked again. This
leads to lost events and is bad.
The second problem is that any triggered listener that throws an error
of the fatal kind will not lead to that error because caught by the
uncaught exception handler. This is because the triggered listener is
executed as a future task under a scheduled thread pool executor. A
throwable there goes caught by the JDK framework and set as the outcome
on the future task. Since we never inspect these tasks for their
outcomes, nor is there a good place to do this, we have to handle these
errors ourselves. To do this, we catch them and dispatch them to the
uncaught exception handler via a forked thread. This is similar to our
handling in Netty.
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