6
$\begingroup$

In exploring Working with DynamicModule: Tracking the progress of Initialization, I came across this. The following usually shows a value for x of 300000 to 400000 after initialization. It varies each time.

DynamicModule[{x}, Dynamic[x], Initialization :> (x = 1;
   Do[x = i, {i, 10000000}];
   x = 2;
   Do[x = i, {i, 10000000}];
   x = 3;)]

If the option SynchronousInitialization -> True is set, a similar thing happens, although the displayed value for x ranged from 18000 to 9900000. On the other hand, if SynchronousInitialization -> False is set, the displayed value is 3, as expected.

Is this a bug, or is it to be expected, due to some aspect of the dynamic updating system I'm not aware of?

Version: 10.0.0, 9.0.1, and 8.0.4; Max OSX 10.9.4.

Improve this question
$\endgroup$

1 Answer 1

Reset to default
7
$\begingroup$

SynchronousInitialization -> True causes dynamic evaluations to occur on the preemptive link. This locks up the notebook front-end for the duration of an evaluation. To avoid locking up the front-end indefinitely, there is a default timeout of six seconds:

CurrentValue[EvaluationNotebook[], DynamicEvaluationTimeout]
(* 6. *)

The values we see for x are simply those that have been set prior to the timeout.

On my machine, it takes about 25 seconds to perform the complete initialization. If I set the timeout to a value higher than that, then I get the expected result:

SetOptions[EvaluationNotebook[], {DynamicEvaluationTimeout -> 60}]

The original motivation for this question aside, it is generally inadvisable to perform long-running evaluations synchronously on the preemptive link. It is especially dangerous to set the timeout to infinity or a large number because it disables the ability to terminate a runaway calculation.

Improve this answer
$\endgroup$
1
  • $\begingroup$ Thanks. I think this must be right. When I first noticed, I had timed the do-loop at just under a second and substituted it for Pause[1]. This morning it's taking 2.6 sec. and the complete initialization code on its own takes 5.3 sec. If I put SessionTime[] in cells before and after the DynamicModule, the difference is slightly over 6 sec. I knew about the time constraint, but thought I was within that time. I must have been mistaken last night about the timing of the loop. I also thought there would be a warning if it timed out. $\endgroup$
    – Michael E2
    Commented Sep 18, 2014 at 11:34

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.