controller <- crew::crew_controller_local(
  seconds_launch = 120,
  workers = 20L,
  seconds_idle = 5,
  seconds_exit = 5
)
controller$start()
for (i in seq_len(6000)) {
  print(i)
  controller$push(
    command = targets:::target_run(target, globalenv(), "_targets"),
    data = list(target = targets::tar_target(y, tibble::tibble(x = x, a = 1, b = 2, c = "3"))), 
  )
  tmp <- controller$pop()
}
while (!controller$empty()) {
  out <- controller$pop()
  if (!is.null(out)) {
    print(out$name)
  }
}
controller$terminate()

[1] "162217f067283e9c493c253ef92d77872c032373"
[1] "f840548352495f2ffb71b1b08e05db14ae022a05"
[1] "af1267432fb1f3bba52b9d28472c21c8a50768b2"
[1] "7e03d62698d4684c59e5e3a532a3e98624970413"
...

Error in `attributes<-`(res, list(dim = c(length(envir[["urls"]]), 4L),  : 
  dims [product 80] do not match the length of object [65]
In addition: Warning messages:
1: In is.character(r) && nzchar(r) :
  'length(x) = 49 > 1' in coercion to 'logical(1)'
2: In envir[["urls"]][i] <- r :
  number of items to replace is not a multiple of replacement length
3: In self$workers$socket[index] <- socket :
  number of items to replace is not a multiple of replacement length
4: In recv(sock, mode = mode, block = timeout) :
  received data could not be converted to integer