The future.callr package implements the Future API on top of callr. The Future API is defined by the future package.
Details
To use callr futures, load future.callr, and
select the type of future you wish to use, e.g. plan(callr).
See also
Examples
# \donttest{
plan(callr)
demo("mandelbrot", package = "future", ask = FALSE)
#>
#>
#> demo(mandelbrot)
#> ---- ~~~~~~~~~~
#>
#> > library("future")
#>
#> > library("graphics")
#>
#> > plot_what_is_done <- function(counts) {
#> + for (kk in seq_along(counts)) {
#> + f <- counts[[kk]]
#> +
#> + ## Already plotted?
#> + if (!inherits(f, "Future")) next
#> +
#> + ## Not resolved?
#> + if (!resolved(f)) next
#> +
#> + message(sprintf("Plotting tile #%d of %d ...", kk, n))
#> + counts[[kk]] <- value(f)
#> + screen(kk)
#> + plot(counts[[kk]])
#> + }
#> +
#> + counts
#> + }
#>
#> > ## Options
#> > region <- getOption("future.demo.mandelbrot.region", 1L)
#>
#> > if (!is.list(region)) {
#> + if (region == 1L) {
#> + region <- list(xmid = -0.75, ymid = 0.0, side = 3.0)
#> + } else if (region == 2L) {
#> + region <- list(xmid = 0.283, ymid = -0.0095, side = 0.00026)
#> + } else if (region == 3L) {
#> + region <- list(xmid = 0.282989, ymid = -0.01, side = 3e-8)
#> + }
#> + }
#>
#> > nrow <- getOption("future.demo.mandelbrot.nrow", 3L)
#>
#> > resolution <- getOption("future.demo.mandelbrot.resolution", 400L)
#>
#> > delay <- getOption("future.demo.mandelbrot.delay", interactive())
#>
#> > if (isTRUE(delay)) {
#> + delay <- function(counts) Sys.sleep(1.0)
#> + } else if (!is.function(delay)) {
#> + delay <- function(counts) {}
#> + }
#>
#> > ## Generate Mandelbrot tiles to be computed
#> > Cs <- mandelbrot_tiles(xmid = region$xmid, ymid = region$ymid,
#> + side = region$side, nrow = nrow,
#> + resolution = resolution)
#>
#> > if (interactive()) {
#> + dev.new()
#> + plot.new()
#> + split.screen(dim(Cs))
#> + for (ii in seq_along(Cs)) {
#> + screen(ii)
#> + par(mar = c(0, 0, 0, 0))
#> + text(x = 1 / 2, y = 1 / 2, sprintf("Future #%d\nunresolved", ii), cex = 2)
#> + }
#> + } else {
#> + split.screen(dim(Cs))
#> + }
#> [1] 1 2 3 4 5 6 7 8 9
#>
#> > ## Create all Mandelbrot tiles via lazy futures
#> > n <- length(Cs)
#>
#> > message(sprintf("Creating %d Mandelbrot tiles:", n), appendLF = FALSE)
#> Creating 9 Mandelbrot tiles:
#>
#> > counts <- lapply(seq_along(Cs), FUN=function(ii) {
#> + message(" ", ii, appendLF = FALSE)
#> + C <- Cs[[ii]]
#> + future({
#> + message(sprintf("Calculating tile #%d of %d ...", ii, n), appendLF = FALSE)
#> + fit <- mandelbrot(C)
#> +
#> + ## Emulate slowness
#> + delay(fit)
#> +
#> + message(" done")
#> + fit
#> + }, lazy = TRUE)
#> + })
#> 1
#> 2
#> 3
#> 4
#> 5
#> 6
#> 7
#> 8
#> 9
#>
#> > message(".")
#> .
#>
#> > ## Calculate and plot tiles
#> > repeat {
#> + counts <- plot_what_is_done(counts)
#> + if (!any(sapply(counts, FUN = inherits, "Future"))) break
#> + }
#> Plotting tile #1 of 9 ...
#> Error: CallrFuture (<none>) failed. The reason reported was ‘! in callr subprocess.
#> Caused by error:
#> ! Argument 'strategiesR' is a function, but does not inherit 'future': ‘function’’. Post-mortem diagnostic: The parallel worker (PID 333906) started at 2024-12-30T23:25:13+0000 finished with exit code 0. The total size of the 4 globals exported is 328.23 KiB. The three largest globals are ‘C’ (280.80 KiB of class ‘complex’), ‘delay’ (47.36 KiB of class ‘function’) and ‘ii’ (35 bytes of class ‘numeric’)
# }
