targets + crew for parallel builds

In targets, by default, targets are dispatched to be built one at a time, but we can use crew so that multiple workers can build targets in parallel. Here is the code to add to _targets.R to get 2 workers.

targets::tar_option_set(
  controller = crew::crew_controller_local(workers = 2)
)

And then you can view how much work each worker did. (I’m hard-coding the returns to show what happened with a full site build.)

targets::tar_crew()
#>   controller               worker seconds targets
#>   <chr>                     <int>   <dbl>   <int>
#> 1 8f28e966dd6adaf60895eb01      1    49.4      32
#> 2 8f28e966dd6adaf60895eb01      2    25.1       9