a5_threads: Get or set the number of threads used by a5R

In a5R: 'A5' Discrete Global Grid System

Get or set the number of threads used by a5R

Description

Controls the number of threads used for parallel processing in vectorised functions. One thread (the default) runs sequentially with no overhead; more run in parallel via rayon. As with options() and par(), a5_threads() reports the current count and a5_threads(n) sets it.

Usage

a5_threads(n = NULL)

## S3 method for class 'a5_threads'
with(data, expr, ...)

Arguments

n	NULL (the default) to report the current count, or an integer scalar of at least 1 to set it. The value returned by an earlier a5_threads(n) call also works.
data	The value of a5_threads(n).
expr	Code to run with that thread count.
...	Unused.

Details

a5_threads(n) returns the previous thread count, so a change can be scoped to a block of code with with(), as mirai::daemons() is: with(a5_threads(4), expr) runs expr on four threads and then restores the previous count, even if expr fails.

The count can also be set before the package loads, with the option a5R.threads or the environment variable A5R_NUM_THREADS.

A forked worker, as created by parallel::mclapply() or future::multicore, inherits the count but not the threads, so a5R runs on one thread there until the worker calls a5_threads() itself. Separate-process workers, as from mirai or future::multisession, start at one thread like any new session.

Value

a5_threads(): the current count, an integer scalar. a5_threads(n): the previous count, invisibly, as an a5_threads object. with(): the value of expr.

Examples

a5_threads()

cells <- a5_lonlat_to_cell(runif(1000, -180, 180), runif(1000, -80, 80), 10)
b <- with(a5_threads(2), a5_cell_to_boundary(cells))
a5_threads()

a5R documentation built on Oct. 19, 2026, 5:08 p.m.