# Aborting from inside a ScheduledTask

If you have an Abort[] inside a ScheduledTask expression, what does it abort? The scheduled task evaluation, or any main kernel evaluation that is ongoing?

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have you tried it? –  belisarius Dec 6 '13 at 15:57
Yes, and I know the answer. I'm contributing this question which came to me from a Mathematica user because (a) it's not necessarily obvious what it should do and (b) it's not currently documented. –  Joel Klein Dec 6 '13 at 22:27
My guess/expectation is that it would only abort whatever is being evaluated in the task. What is the answer? –  Mike Honeychurch Dec 6 '13 at 22:32
I tried and it only aborts the task. An explanation would be nice since you know the internals :-) How does this functionality even work? Does it depend on anything outside of the kernel (e.g. Java)? Are these pre-emptive evaluations (like Button by default)? Is the functionality exactly the same as InternalPeriodicals or different? –  Szabolcs Dec 7 '13 at 0:48
It is strongly recommended to self answer, the more that your answer would be the most reliable here :) –  Kuba Dec 7 '13 at 9:44

Abort[] inside a scheduled task will abort the rest of the task expression at the given time, not any main evaluation. It will also repeat to evaluate the task (up till the Abort[]) if further time slots are scheduled.

To show this, first start a scheduled task:

RunScheduledTask[
Print[DateString[], " Scheduled task before Abort[]"]; Abort[];
Print[DateString[], " Scheduled task after Abort[]"], {5, 3}, 5]


By itself you can see that the scheduled task expression gets aborted: in the Messages window you will see the "before" Print output, but not the "after".

While this is running, start a long-running evaluation in a cell:

Print["Mersenne primes:"];
Do[
With[{n = 2^i - 1, i = i},
If[PrimeQ[n], Print[HoldForm[2^i - 1 == n]]]
],
{i, 10^6}
]


This keeps evaluating even when the scheduled task issues its Abort.

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I have included some clarification, hope you don't mind! –  István Zachar Dec 10 '13 at 20:51
That's great, thank you! –  Joel Klein Dec 10 '13 at 22:21
@JoelKlein After starting the long-running evaluation I do not see messages from the ScheduledTask` no more (I use v. 8.0.4). Why this happens? –  Alexey Popkov Dec 13 '13 at 19:13