The default is to use synchronous futures, but this default
can be overridden via R options, system environment variables and
command-line options as explained below as well as in
help("future.options", package = "future").
The default strategy for resolving futures can be controlled via R
option future.plan. For instance, if we add
to our ~/.Rprofile startup script, the future package
will resolve futures in parallel (asynchronously using all available
cores), i.e.
Option future.plan is ignored if command-line option
--parallel (-p) is specified.
An alternative to using options() for setting option
future.plan is to specify system environment variable
R_FUTURE_PLAN. If set, then the future package will set
future.plan accordingly when loaded. For
example,
$ export R_FUTURE_PLAN=multisession
$ Rscript -e "class(future::plan())"
[1] "multisession" "future" "function"Environment variable R_FUTURE_PLAN is ignored if either
option future.plan or command-line option
--parallel (-p) is specified.
When loaded, the future package checks for the command-line option
--parallel=ncores (short -p ncores) and sets
the future strategy (via option future.plan) and the number
of available cores (via option mc.cores) accordingly. This
provides a convenient mechanism for specifying parallel future
processing from the command line. For example, if we start R with
then future will interpret this as we wish to resolve futures in parallel using 2 cores. More specifically, we get that
> availableCores()
mc.cores
2
> class(future::plan())
[1] "FutureStrategy" "tweaked" "multisession" "future" "function"We can use this command-line option also with Rscript,
which provides a convenient mechanism for launching future-enhanced R
scripts such that they run in parallel, e.g.
This does, of course, require that the script uses futures and the future package.
If --parallel=1 is specified, or equivalently
-p 1, then futures are resolved using a single process.
Specifying these command-line options override any other startup settings.