Minimalist async evaluation framework for R.

未来 みらい mirai is Japanese for ‘future’.

Extremely simple and lightweight method for concurrent / parallel code execution, built on ‘nanonext’ and ‘NNG’ (Nanomsg Next Gen) technology.

Whilst frameworks for parallelisation exist for R, {mirai} is designed for simplicity.

mirai() returns a ‘mirai’ object immediately.

A ‘mirai’ evaluates an arbitrary expression asynchronously, resolving automatically upon completion.

{mirai} has a tiny pure R code base, relying solely on {nanonext}, a lightweight binding for the NNG C library with no package dependencies.

Installation

Install the latest release from CRAN:

or the development version from rOpenSci R-universe:

install.packages("mirai", repos = "https://shikokuchuo.r-universe.dev")

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Example 1: Compute-intensive Operations

Use case: minimise execution times by performing long-running tasks concurrently in separate processes.

Multiple long computes (model fits etc.) can be performed in parallel on available computing cores.

Use mirai() to evaluate an expression asynchronously in a separate, clean R process.

A ‘mirai’ object is returned immediately.

library(mirai)

m <- mirai({
  res <- rnorm(n) + m
  res / rev(res)
}, n = 1e8, m = runif(1))

m
#> < mirai >
#>  - $data for evaluated result

Above, all named objects are passed through to the mirai.

The ‘mirai’ yields an ‘unresolved’ logical NA value whilst the async operation is ongoing.

m$data
#> 'unresolved' logi NA

Upon completion, the ‘mirai’ resolves automatically to the evaluated result.

m$data |> str()
#>  num [1:100000000] 1.4735 -1.7795 -0.3405 -4.1733 0.0306 ...

Alternatively, explicitly call and wait for the result using call_mirai().

call_mirai(m)$data |> str()
#>  num [1:100000000] 1.4735 -1.7795 -0.3405 -4.1733 0.0306 ...

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Example 2: I/O-bound Operations

Use case: ensure execution flow of the main process is not blocked.

High-frequency real-time data cannot be written to file/database synchronously without disrupting the execution flow.

Cache data in memory and use mirai() to perform periodic write operations concurrently in a separate process.

A ‘mirai’ object is returned immediately.

Below, .args accepts a list of objects already present in the calling environment to be passed to the mirai.

library(mirai)

x <- rnorm(1e6)
file <- tempfile()

m <- mirai(write.csv(x, file = file), .args = list(x, file))

unresolved() may be used in control flow statements to perform actions which depend on resolution of the ‘mirai’, both before and after.

This means there is no need to actually wait (block) for a ‘mirai’ to resolve, as the example below demonstrates.

# unresolved() queries for resolution itself so no need to use it again within the while loop

while (unresolved(m)) {
  cat("while unresolved\n")
  Sys.sleep(0.5)
}
#> while unresolved
#> while unresolved

cat("Write complete:", is.null(m$data))
#> Write complete: TRUE

Now actions which depend on the resolution may be processed, for example the next write.

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Daemons

Daemons or persistent background processes may be set to receive ‘mirai’ requests.

This is potentially more efficient as new processes no longer need to be created on an ad hoc basis.

# create 8 daemons
daemons(8)
#> [1] 8

# view the number of active daemons
daemons("view")
#> [1] 8

The current implementation is low-level and ensures tasks are evenly-distributed amongst daemons without actively managing a task queue.

This robust and resource-light approach is particularly well-suited to working with similar-length tasks, or where the number of concurrent tasks typically does not exceed the number of available daemons.

# reset to zero
daemons(0)
#> [1] -8

Set the number of daemons to zero again to revert to the default behaviour of creating a new background process for each ‘mirai’ request.

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Deferred Evaluation Pipe

{mirai} implements a deferred evaluation pipe %>>% for working with potentially unresolved values.

Pipe a mirai $data value forward into a function or series of functions and it initially returns an ‘unresolvedExpr’.

The result may be queried at $data, which will return another ‘unresolvedExpr’ whilst unresolved. However when the original value resolves, the ‘unresolvedExpr’ will simultaneously resolve into a ‘resolvedExpr’, for which the evaluated result will be available at $data.

It is possible to use unresolved() around a ‘unresolvedExpr’ or its $data element to test for resolution, as in the example below.

The pipe operator semantics are similar to R’s base pipe |>:

x %>>% f is equivalent to f(x)
x %>>% f() is equivalent to f(x)
x %>>% f(y) is equivalent to f(x, y)

m <- mirai({Sys.sleep(0.5); 1})
b <- m$data %>>% c(2, 3) %>>% as.character()
b
#> < unresolvedExpr >
#>  - $data to query resolution
b$data
#> < unresolvedExpr >
#>  - $data to query resolution
Sys.sleep(1)
b$data
#> [1] "1" "2" "3"
b
#> < resolvedExpr: $data >

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Errors and Timeouts

If execution in a mirai fails, the error message is returned as a character string of class ‘miraiError’ and ‘errorValue’ to facilitate debugging.

m1 <- mirai(stop("occurred with a custom message", call. = FALSE))
cat(call_mirai(m1)$data)
#> Error: occurred with a custom message

m2 <- mirai(mirai())
cat(call_mirai(m2)$data)
#> Error in mirai() : missing expression, perhaps wrap in {}?
#> Calls: <Anonymous> -> eval -> eval -> mirai

is_mirai_error(m2$data)
#> [1] TRUE
is_error_value(m2$data)
#> [1] TRUE

If execution of a mirai surpasses the timeout set via the .timeout argument, the mirai will resolve to an errorValue. This can, amongst other things, guard against mirai processes that hang and never return.

m3 <- mirai(nanonext::msleep(1000), .timeout = 500)
call_mirai(m3)$data
#> Warning in (function (x) : 5 | Timed out
#> 'errorValue' int 5

is_mirai_error(m3$data)
#> [1] FALSE
is_error_value(m3$data)
#> [1] TRUE

is_error_value() tests for both mirai execution errors and timeouts. is_mirai_error() tests for just mirai execution errors.

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{mirai} website: https://shikokuchuo.net/mirai/
{mirai} on CRAN: https://cran.r-project.org/package=mirai

{nanonext} website: https://shikokuchuo.net/nanonext/
{nanonext} on CRAN: https://cran.r-project.org/package=nanonext

NNG website: https://nng.nanomsg.org/

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Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.