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$SynchronousEvaluation

is a symbol whose value is True if it is evaluated as part of a synchronous evaluation.

Details
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Examples  
Basic Examples  
Scope  
Properties & Relations  
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$SynchronousEvaluation

$SynchronousEvaluation

is a symbol whose value is True if it is evaluated as part of a synchronous evaluation.

Details

  • A synchronous evaluation is generally triggered by controls in the front end. Controls that may generate synchronous evaluations include Button, EventHandler, and any control that takes a Dynamic value.
  • Manipulate may trigger synchronous evaluations, depending upon the value of the SynchronousUpdating and SynchronousInitialization options.
  • A synchronous evaluation is the same as a preemptive evaluation. Some controls, such as Button and EventHandler, support an option setting of Method->"Preemptive", which causes the control's evaluations to be synchronous.
  • Synchronous evaluations halt the system while being evaluated. A typical use of $SynchronousEvaluation is to write code that should behave differently to prevent halting the system excessively.

Examples

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Basic Examples  (2)

Typical shift-return evaluations are asynchronous:

Wolfram Language code: $SynchronousEvaluation

Evaluations within Dynamic are synchronous by default:

Wolfram Language code: Dynamic[$SynchronousEvaluation]

Scope  (2)

Evaluations within DynamicModule Initialization are synchronous by default:

Wolfram Language code: DynamicModule[{init}, Dynamic[init], Initialization :> (init = $SynchronousEvaluation)]

Manipulate has a different default for SynchronousUpdating:

Wolfram Language code: Manipulate[Plot[Sin[a x], {x, 0, 10}, PlotLabel -> $SynchronousEvaluation], {a, 1, 5}]

Properties & Relations  (3)

By default, Button and similar constructs do synchronous evaluation:

Wolfram Language code: Button["synchronous?", Print[$SynchronousEvaluation]]

With the option Method->"Queued", the evaluation is done asynchronously:

Wolfram Language code: Button["synchronous?", Print[$SynchronousEvaluation], Method -> "Queued"]

Synchronous evaluation in Dynamic is controlled by the SynchronousUpdating option:

Wolfram Language code: {Dynamic[$SynchronousEvaluation], Dynamic[$SynchronousEvaluation, SynchronousUpdating -> False]}

The initialization of DynamicModule is controlled by the SynchronousInitialization option:

Wolfram Language code: DynamicModule[{init}, Dynamic[init], Initialization :> (init = $SynchronousEvaluation), SynchronousInitialization -> False]
Wolfram Research (2015), $SynchronousEvaluation, Wolfram Language function, https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html.

Text

Wolfram Research (2015), $SynchronousEvaluation, Wolfram Language function, https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html.

CMS

Wolfram Language. 2015. "$SynchronousEvaluation." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html.

APA

Wolfram Language. (2015). $SynchronousEvaluation. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html

BibTeX

@misc{reference.wolfram_2026_$synchronousevaluation, author="Wolfram Research", title="{$SynchronousEvaluation}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html}", note=[Accessed: 12-June-2026]}

BibLaTeX

@online{reference.wolfram_2026_$synchronousevaluation, organization={Wolfram Research}, title={$SynchronousEvaluation}, year={2015}, url={https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html}, note=[Accessed: 12-June-2026]}