How can I programmatically check from a preemptive evaluation whether a main evaluation is currently ongoing?
I need a function mainEvaluationOngoingQ[] so that
Button["Evaluating?", Print@mainEvaluationOngoingQ[], Method -> "Preemptive"]
will print True only if a main evaluation is ongoing.
If you control the launch of the main evaluation process, then a very simple way is to wrap your code in a dynamic environment (Block), which would set some flag:
mainEvaluationOngoingQ[] := TrueQ@mainEvaluationQ
Block[{mainEvaluationQ = True}, Do[i^2, {i, 1, 10^8}]]
You can automate this by creating an environment:
SetAttributes[withMainEvaluation, HoldAll];
withMainEvaluation[code_] :=
Block[{mainEvaluationQ = True}, code]
You can further automate this with $Pre, if needed: $Pre = withMainEvaluation.
Method->"Queued". Any way to cover those cases too?
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withMainEvaluation. If not, one can probably write code which would pre-process a notebook and change that at the box level. Other than that, I don't know how to do this - this may need some lower-level stuff.
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Commented
Feb 9, 2012 at 18:11
Method->"Queued", the evaluation is queued to be evaluated using the main link, so there by definition isn't a (-nother) main evaluation running, and mainEvaluationOngoing always returns False, which is correct when interpreted as "is another main evaluation ongoing". Or am I missing something?
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Commented
May 22, 2013 at 14:05
The following works with Mathematica 8.0.0.0:
Button["Evaluating?",Print@(Drop[Stack[],-7]!={}),Method->"Preemptive"]
However the -7 here is an empirical factor which removes all those entries generated from executing the button code itself; it changes depending on the exact form of the code the Stack[] is embedded in, and might even depend on the Mathematica version (I don't think the inner mechanics of Button is documented, let alone guaranteed never to change).
