nbrOfWorkers() returns a positive number in \({1, 2, 3, ...}\), which
for some future backends may also be +Inf.
nbrOfFreeWorkers() returns a non-negative number in
\({0, 1, 2, 3, ...}\) which is less than or equal to nbrOfWorkers().
Arguments
evaluator
A future evaluator function.
If NULL (default), the current evaluator as returned
by plan() is used.
background
If TRUE, only workers that can process a future in the
background are considered. If FALSE, also workers running in the main R
process are considered, e.g. when using the 'sequential' backend.