Measuring and displaying the current elapsed time of a parallel task with mirai_map and ExtendedTask

[olivier7121]

I want to measure the current elapsed time of a task performed in parallel with the help of mirai_map and shiny::ExtendedTask.

Building on the following example code Shiny ExtendedTask: mirai map, I tried to add this timer but it doesn't move beyond 1 second. What did I do wrong?

library(shiny)
library(bslib)
library(mirai)

ui <- page_fluid(
	titlePanel("ExtendedTask Map Demo"),
	hr(),
	textOutput("Timer"),
	p("Perform 4 calculations that each take between 1 and 4 secs to complete:"),
	input_task_button("calculate", "Calculate"),
	p(textOutput("result")),
	tags$style(type="text/css", "#result {white-space: pre-wrap;}")
)

server <- function(input, output) {
	
	Timer.Start <- reactiveVal(0)
	Timer.End <- reactiveVal(0)
	Timer.Status <- reactiveVal(0)
	
	task <- ExtendedTask$new(function() {
		mirai_map(1:4, function(i) {
			# simulated long calculation
			Sys.sleep(i)
			sprintf(
				"Calc %d | PID %d | Finished at %s.", i, Sys.getpid(), format(Sys.time())
			)
		})
	}) |> bind_task_button("calculate")
	
	observeEvent(input$calculate, {
		Timer.Start(as.integer(Sys.time()))
		Timer.Status(1)
		task$invoke()
	})
	
	output$Timer <- renderText({
		Status <- Timer.Status()
		if(Status == 1)
		{
			invalidateLater(1000)
			Timer.End(as.integer(Sys.time()))
			paste("Time elapsed:", format(as.POSIXct(Timer.End() - Timer.Start() - 3600L), "%H:%M:%S"))
		} else if(Status == 2)
		{
			paste("Time elapsed:", format(as.POSIXct(Timer.End() - Timer.Start() - 3600L), "%H:%M:%S"))
		}
	})

	output$result <- renderText({
		# result of mirai_map() is a list
		Timer.Status(2)
		as.character(task$result())
	}, sep = "\n")
	
	# output$current_time <- renderText({
	# 	invalidateLater(1000)
	# 	format(Sys.time(), "%H:%M:%S %p")
	# })
}

app <- shinyApp(ui, server)
with(daemons(4), runApp(app))