Correct Implementation of Multiple Promises with Progress Update in R Shiny?

Question

I am developing a Shiny application where I need to score a series of articles asynchronously by calling an external API using my own package. I aim to run multiple promises in parallel to enhance performance and wish to update a progress bar after each promise completes.

Here's the code in the server side of the app, inside a withProgress() block:

    # Set up reactive values
    articles <- reactiveVal()
    articles(get_articles())
    scored_articles <- reactiveVal()

    # Set up parallel environment
    old_plan <- future::plan()
    future::plan(future::multisession)
    on.exit(future::plan(old_plan), add = TRUE)
    
    # Progress bar parameters init
    incProgress(.5)
    batch_size <- 20
    tot_items <- articles() |> nrow()
    
    # Score articles
    promises <- articles() |>
      group_by(grp = ceiling(row_number()/batch_size)) |> # Split dataset into chunks
      group_split() |>
      furrr::future_map(\(df) {
        message("Promise launched")
        promises::future_promise({
          score <- get_llm_score(df)
          incProgress(.5 / (tot_items/batch_size))
          score
        })
      })

    # Solve the promises
    promises::promise_all(.list = promises) |>
      promises::then(function(result) {
        # post-processing the result
        result |> bind_rows() |>
        scored_articles()
      }) |>
      promises::catch(function(error) {
        message(error)
        showNotification("An error occurred", type = "error")
      })

Something doesn't work in this implementation. This is what happens:

The bar gets stuck at 50% (the value that it should have before starting the promise).
The "Promise launched" messages are triggered much later, presumably AFTER the call to get_llm_score() has been completed, instead of before.
The progress bar then disappears. My hypothesis is that it gets updated all at once after all the promises have been fulfilled.
Then nothing happens. The app should row bind the loop output and put it into scored_articles() which should trigger the rendering of the table.

What am I doing wrong? is this the correct way to run a repeated process in parallel? how should I implement it in order to have a starting message before my function is run and a progress update once it's done?

Any insights or recommendations would be greatly appreciated.

Correct Implementation of Multiple Promises with Progress Update in R Shiny?

0 Answers0