Shiny - Render multiple outputs in parallel - r

Question

When I want to render multiple outputs linked to a single observer, they are rendered after both outputs are calculated. If there is a long calculation between the outputs it takes a long time before all outputs are displayed.
Is it possible in a Shiny application to render outputs, linked to a single observer, individually or in parallel? Instead of waiting with rendering until all outputs are calculated.
Example
library(shiny)
ui <- fluidPage(
actionButton('button', 'klik'),
textOutput('first'),
textOutput('second')
)
server <- function(input, output, session) {
observeEvent({input$button},{
output$first <- renderText({Sys.Date()})
Sys.sleep(10)
output$second <- renderText({Sys.Date()})
})
}
shinyApp(ui, server)

Answer 1

Thanks to #BertilBaron I found out a way to avoid waiting for long calculations in R-Shiny. The article that I used can be found here.
Basically what you do is to run each process in parallel using the package future. With this package every time the user clicks on the button the calculation will be performed. So keep in mind that you have to build in a block for impatient users.
My working example
library(shiny)
library(promises)
library(future)
plan(multiprocess)
ui <- fluidPage(
actionButton('button', 'klik'),
textOutput('first'),
textOutput('second')
)
server <- function(input, output) {
nclicks <- reactiveVal(0)
nclicks2 <- reactiveVal(0)
result_val <- reactiveVal()
result_val2 <- reactiveVal()
observeEvent(input$button,{
# Don't do anything if analysis is already being run
if(nclicks() != 0 | nclicks2() != 0){
showNotification("Already running analysis")
return(NULL)
}
# Increment clicks and prevent concurrent analyses
nclicks(nclicks() + 1)
nclicks2(nclicks2() + 1)
result <- future({
# Long Running Task
Sys.sleep(10)
#Some results
Sys.time()
}) %...>% result_val()
result2 <- future({
#Some results
Sys.time()
}) %...>% result_val2()
# Catch inturrupt (or any other error) and notify user
result <- catch(result,
function(e){
result_val(NULL)
print(e$message)
showNotification(e$message)
})
result2 <- catch(result2,
function(e){
result_val2(NULL)
print(e$message)
showNotification(e$message)
})
# After the promise has been evaluated set nclicks to 0 to allow for anlother Run
result <- finally(result,
function(){
nclicks(0)
})
result2 <- finally(result2,
function(){
nclicks2(0)
})
# Return something other than the promise so shiny remains responsive
NULL
})
output$first <- renderText({
req(result_val())
})
output$second <- renderText({
req(result_val2())
})
}
# Run the application
shinyApp(ui = ui, server = server)