resolve "no applicable method for 'mutate'" error

saw:

```
> Error in UseMethod("mutate") :
  no applicable method for 'mutate' applied to an object of class "NULL"
```

...intermittently for some calls. turns out this was because the session had a longer-than-expected delay before its results were able to be `read()`--just iteratively query with additional delay until we get results.

R/syrup.R

@@ -120,28 +120,12 @@ syrup <- function(expr, interval = .5, peak = FALSE, env = caller_env()) {
 
  # tell `sesh` to stop taking snapshots
  file.remove(keep_going_file)
- Sys.sleep(interval + .1)
+ Sys.sleep(interval + .2)
 
- # grab the result from sesh and close it
- sesh_res <- sesh$read()
- sesh$close()
+ res <- retrieve_results(sesh)
 
  withr::deferred_clear()
 
- # return the memory usage information
- res <- sesh_res$result
-
- if (is.null(res)) {
- if (!is.null(sesh_res$error)) {
- stop(gsub("\n", " ", conditionMessage(sesh_res$error)))
- } else {
- stop(paste0("Class: ", paste0(class(sesh_res), collapse = ""),
- "Code: ", sesh_res$code,
- " Message: ", sesh_res$message,
- " stderr: ", sesh_res$stderr))
- }
- }
-
  if (identical(res$id[length(res$id)], 1) && !isTRUE(peak)) {
  rlang::warn(c(
  "!" = "`expr` evaluated fully before syrup could take a snapshot of memory usage.",

R/utils.R

@@ -40,3 +40,27 @@ calculate_pct_cpu <- function(time, user, system) {
 
  c(NA_real_, (user_diffs + system_diffs) * 100 / intervals)
 }
+
+# grab the result from sesh and close it.
+# may be a slightly longer delay before sesh is able to return, so iteratively
+# query until we get a result back.
+retrieve_results <- function(sesh, call = caller_env()) {
+ sesh_res <- sesh$read()
+ cnt <- 1
+ while (is.null(sesh_res) & cnt < 10) {
+ Sys.sleep(.2)
+ sesh_res <- sesh$read()
+ cnt <- cnt + 1
+ }
+
+ sesh$close()
+
+ if (cnt == 10) {
+ cli::cli_abort(
+ "Unable to retrieve resource usage results from the temporary session.",
+ .internal = TRUE
+ )
+ }
+
+ sesh_res$result
+}