This option controls the number of threads used by datatable for parallel calculations.
nthreads value. Initially, this option is set to
the value returned by C++ call
and usually equals to the number of available cores.
nthreads value. It can be greater or smaller than the initial setting.
For example, setting
nthreads = 1 will force the library into
a single-threaded mode. Setting
0 will restore
the initial value equal to the number of processor cores.
nthreads to a value less than
0 is equivalent to requesting
that fewer threads than the maximum.