How do I wrap a blocking function into a promise RShiny - r

Question

I have an R Shiny dashboard that has 2 observers that are set to refresh at specific times, One observer refreshes every 6 hours, the other every 2 mins. Both observers run a function that returns a reactive value. This works fine, however every 6 hours when the first observer is triggered it locks the dashboard and prevents the other observer from functioning. After some reading I know that I need to use futures and promises but am unable to implement anything that works as intended. How do I wrap the functions in each observer into respective futures that would prevent blocking?
values <- reactiveValues()
observe({
# Re-execute this reactive expression every 2 mins
invalidateLater(120000, session)
values$twominresult <- twoMinFunction()
})
observe({
# Re-execute this reactive expression every 6 hours
invalidateLater(21600000, session)
values$sixhourresult <- sixhourfunction()
})

Answer 1

Here is an example for intra-session non-blocking futures based on your code snippets:
library(shiny)
library(promises)
library(future)
plan(multiprocess)
twoMinFunction <- function(){
return(Sys.time())
}
sixHourFunction <- function(){
Sys.sleep(3)
return(Sys.time())
}
server <- function(input, output, session) {
values <- reactiveValues(twominresult = NULL, sixhourresult = NULL)
observe({
# Re-execute this reactive expression every 2 seconds # mins
invalidateLater(2000, session) # 120000
myTwoMinFuture <- future({
twoMinFunction()
})
then(myTwoMinFuture, onFulfilled = function(value) {
values$twominresult <- value
},
onRejected = NULL)
return(NULL)
})
observe({
# Re-execute this reactive expression every 6 seconds # hours
invalidateLater(6000, session) # 21600000
mySixHourFuture <- future({
sixHourFunction()
})
then(mySixHourFuture, onFulfilled = function(value) {
values$sixhourresult <- value
},
onRejected = NULL)
return(NULL)
})
output$twominout <- renderText({
paste("two min result:", values$twominresult)
})
output$sixhoursout <- renderText({
paste("six hour result:", values$sixhourresult)
})
}
ui <- fluidPage(textOutput("twominout"),
textOutput("sixhoursout"))
shinyApp(ui, server)
I made it a little faster, so you can see the changes.
Please note the return(NULL) in the observeEvent() - this is hiding the future from its own session - allowing intra-session responsiveness. Please keep in mind that this pattern may cause race conditions if used the wrong way (Please see Joe Cheng's comment, which I already mentioned above)