Created
June 8, 2018 23:36
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Cancellable tasks (without async)
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| base_task_iterator <- function(should_continue, iter_body) { | |
| if (should_continue()) { | |
| iter_body() | |
| later::later(~base_task_iterator(should_continue, iter_body)) | |
| } | |
| invisible() | |
| } | |
| while_task_iterator <- function(cancelExpr, whileExpr, func) { | |
| cancelFunc <- rlang::as_function(rlang::enquo(cancelExpr)) | |
| whileFunc <- rlang::as_function(rlang::enquo(whileExpr)) | |
| origCancelVal <- isolate(try(silent = TRUE, cancelFunc())) | |
| cancelled <- function() { | |
| !identical(origCancelVal, isolate(try(silent = TRUE, cancelFunc()))) | |
| } | |
| base_task_iterator( | |
| function() { | |
| !cancelled() && whileFunc() | |
| }, | |
| func | |
| ) | |
| } | |
| list_task_iterator <- function(cancelExpr, x, func) { | |
| cancelExpr <- rlang::enquo(cancelExpr) | |
| origCancelVal <- isolate(try(silent = TRUE, cancelFunc())) | |
| pos <- 1 | |
| while_task_iterator(!!cancelExpr, pos <= length(x), function() { | |
| i <- pos | |
| pos <<- pos + 1L | |
| func(x[[i]]) | |
| }) | |
| } |
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| library(shiny) | |
| ui <- fluidPage( | |
| actionButton("start_list", "Start 'list' iterator"), | |
| actionButton("start_while", "Start 'while' iterator"), | |
| actionButton("cancel", "Stop") | |
| ) | |
| server <- function(input, output, session) { | |
| observeEvent(input$start_list, { | |
| list_task_iterator(input$cancel, 1:10, function(x) { | |
| message(x) | |
| Sys.sleep(1) | |
| }) | |
| }) | |
| observeEvent(input$start_while, { | |
| # Something's wrong with rlang::as_function, I can't use TRUE, only !FALSE | |
| while_task_iterator(input$cancel, !FALSE, function() { | |
| message(format(Sys.time())) | |
| Sys.sleep(1) | |
| }) | |
| }) | |
| } | |
| shinyApp(ui, server) |
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