future_promise behaves differently on shinyapps.io

[karchjd]

The example app below works for me locally but not on shinyapps.io. Specifically, if you press "Cancel," the task stops locally but not on shinyapps.io. Interestingly, it used to work, even with the same version of the package (in a larger app, see rstudio/rsconnect#1105).

I know this is not the best way to handle aborting, but within the larger app and given the constraints I’m working with, it seems to be the only feasible option.

library(shiny)
future::plan(future::multisession)



# Define UI for application that draws a histogram
ui <- fluidPage(

  # Application title
  titlePanel("Cancelable Async Task"),

  # Sidebar with a slider input for number of bins
  sidebarLayout(
    sidebarPanel(
      actionButton("run", "Run"),
      actionButton("cancel", "Cancel")
    ),

    # Show a plot of the generated distribution
    mainPanel(
      tableOutput("result")
    )
  )
)

long_run_fun <- function(){
  start_time <- Sys.time()
  while (as.numeric(Sys.time() - start_time) < 10) {
    Sys.sleep(0.1)
    if (file.exists(abort_file)) {
      quit()
    }
  }
} 

server <- function(input, output) {
  fut <- NULL

  abort_file_global <- reactiveVal()
  running <- reactiveVal(FALSE)
  result_val <- reactiveVal()

  abort_file <- tempfile()
  abort_file_global(abort_file)
  showNotification("Starting Run")

  observeEvent(input$run, {
    # Don't do anything if in the middle of a run
    if (running()) {
      showNotification("Already Running")
      return(NULL)
    }
    running(TRUE)

    print("Starting Run")
    fut <- promises::future_promise({
      long_run_fun()
    }, globals = c("abort_file", "long_run_fun"))
    promises::then(
      fut,
      function(value) {
        print("Task Completed")
        showNotification("Task Completed")
      }
    )

    promises::catch(
      fut,
      function(e) {
        print("Task Aborted")
        showNotification("Task Aborted")
      }
    )

    promises::finally(fut, function() {
      running(FALSE)
      if (file.exists(abort_file)) {
        file.remove(abort_file)
      }
    })

    # Return something other than the future so we don't block the UI
    return(NULL)
  })


  # Kill future
  observeEvent(input$cancel, {
    abort_file_global()
    file.create(abort_file_global())
  })


  output$result <- renderTable({
    req(result_val())
  })
}

# Run the application
shinyApp(ui = ui, server = server)