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


  • 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.


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Basic Examples  (2)

Typical shift-return evaluations are asynchronous:

Evaluations within Dynamic are synchronous by default:

Scope  (2)

Evaluations within DynamicModule Initialization are synchronous by default:

Manipulate has a different default for SynchronousUpdating:

Properties & Relations  (3)

By default, Button and similar constructs do synchronous evaluation:

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

Synchronous evaluation in Dynamic is controlled by the SynchronousUpdating option:

The initialization of DynamicModule is controlled by the SynchronousInitialization option:

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


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


@misc{reference.wolfram_2020_$synchronousevaluation, author="Wolfram Research", title="{$SynchronousEvaluation}", year="2015", howpublished="\url{https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html}", note=[Accessed: 10-May-2021 ]}


@online{reference.wolfram_2020_$synchronousevaluation, organization={Wolfram Research}, title={$SynchronousEvaluation}, year={2015}, url={https://reference.wolfram.com/language/ref/$SynchronousEvaluation.html}, note=[Accessed: 10-May-2021 ]}


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


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