no progress bar with backend = NULL

[MaximilianPi]

Hi @mihaiconstantin

thanks for the great package. Is it intended that there's no progress bar for backend = NULL?:

parabar::configure_bar(type = "modern", format = "[:bar] :percent :eta", width = getOption("width")/2)
results <- parabar::par_sapply(NULL, 1:100, function(x) {
  # Sleep a bit.
  Sys.sleep(0.01)
  
  # Compute and return.
  x + 1
})

[mihaiconstantin]

Hi @MaximilianPi,

Thanks for reaching out.

Indeed, with backend = NULL, the execution is sequential (i.e., base::sapply in this case), which does not have any progress-tracking or other capabilities, as seen below:

parabar/R/UserApiConsumer.R

Lines 181 to 198 in 2844b4d

	sapply = function(backend, x, fun, ...) {
	# Prepare the sequential operation.
	sequential <- bquote(
	do.call(
	base::sapply, c(list(X = .(x), FUN = .(fun)), .(list(...)))
	)
	)
	# Prepare the parallel operation.
	parallel <- bquote(
	do.call(
	context$sapply, c(list(x = .(x), fun = .(fun)), .(list(...)))
	)
	)
	# Execute the `sapply` operation accordingly and return the results.
	private$.execute(backend, parallel, sequential)
	},

Now, it is straightforward to add progress tracking in this case, but I think it is better suited for the task function itself rather than parabar::par_sapply. At that time, the rationale behind this decision was to keep the architecture clean.

However, I am considering extending the contexts (e.g., ProgressTrackingContext) to also provide the corresponding behavior implementation for sequential operations.

For now, you can still achieve the same using the developer API as follows:

# Instantiate a `ModernBar`.
bar <- ModernBar$new()

# Create the bar.
bar$create(total = 100, initial = 0, format = "[:bar] :percent :eta", width = getOption("width") / 2)

# Run the task sequentially.
results <- parabar::par_sapply(NULL, 1:100, function(x) {
    # Update the progress bar.
    bar$update(x)

    # Sleep a bit.
    Sys.sleep(0.01)

    # Compute and return.
    x + 1
})

# Terminate the bar.
bar$terminate()

I hope this helps.