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")
}

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

[olivier7121]

What I don't understand is that the following snippet without ExtendedTask works (i.e. does what I want) although it should be equivalent to the previous snippet with ExtendedTask (but that's probably where I missed something):

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

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()
		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())
			)
		}) %...>% {
			output$result <- renderText({
				Timer.Status(2)
				as.character(.)
			}, sep = "\n")
			update_task_button(id = "calculate", state = "ready")
		}
		update_task_button(id = "calculate", state = "busy")
	})
	
	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")
}

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

[shikokuchuo]

For your ExtendedTask example, it is here:

	output$result <- renderText({
		# result of mirai_map() is a list
		Timer.Status(2)
		as.character(task$result())
	}, sep = "\n")

Your Timer.Status(2) gets executed straight away and stops the timer.

Here you effectively want the return value of the ExtendedTask, and also want another side effect in stopping the timer.
Using the mirai_map async without ExtendedTask in your second example is a way around this.