Skip to contents

Update progress of a background async task

Source: R/async.R
async_progress.Rd

async_progress allows a long-running background task to send progress updates back to the main application thread. The main thread will automatically capture these updates and refresh the UI loading overlay.

Usage

async_progress(value, message = NULL)

Arguments

value

Numeric value from 0 to 100 representing the progress percentage.

message

Optional character string describing the current step/state. Shown beneath the progress bar in the loading overlay.

Value

Invisible TRUE if progress was written successfully, FALSE if the progress file path is not set (e.g. outside a background task).

Details

Call this function from inside the function passed to async() or rdesk_async(). It writes a JSON progress record to a temporary file that the main event loop polls every iteration. The file is cleaned up automatically when the job completes.

The progress value should increase monotonically from 0 to 100. The loading overlay in the frontend updates with each new value received.

See also

async(), rdesk_async()

Examples

if (interactive()) {
  app$on_message("heavy_task", async(function(payload) {
    for (i in 1:10) {
      Sys.sleep(0.5)
      async_progress(i * 10, paste("Step", i, "of 10"))
    }
    "done"
  }, app = app))
}