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Intra-session reactivity in Shiny.

shiny.worker allows you to delegate heavy computation tasks to a separate process, such that it does not freeze your Shiny app.

How to install?

Pick the stable version from CRAN:


or the latest from GitHub:



See live example here or more examples with code in the examples/ folder.

How to use it?

Initialise your worker at the beggining of your app.

worker <- initialize_worker()

Then, in the server of your Shiny app define a promise that returns a reactive when your heavy job will be completed.

my_heavy_calculations <- function(args) {
  # ...

# this reactive object is used to trigger the job start,
# but also to pass parameters to the function
reactive_arguments <- reactive({
  list(r = rnorm(1))

# resultPromise will be a reactive value with results returned by my_heavy_calculations
resultPromise <- worker$run_job("job1", my_heavy_calculations, args_reactive = reactive_arguments)

resultPromise()$result # contains the result of the calculations
resultPromise()$resolved # contains flag that informs whether the job has finished or not


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