grapes-dorng-grapes: Reproducible Parallel Foreach Backend

In doRNG: Generic Reproducible Parallel Backend for 'foreach' Loops

Reproducible Parallel Foreach Backend

Description

' '

Usage

obj %dorng% ex

Arguments

obj	a foreach object as returned by a call to foreach.
ex	the R expression to evaluate.

Value

' The whole sequence of RNG seeds is stored in the result object as an attribute. Use attr(res, 'rng') to retrieve it.

Global options

These options are for advanced users that develop 'foreach backends:

* 'doRNG.rng_change_warning_skip': if set to a single logical 'FALSE/TRUE', it indicates whether a warning should be thrown if the RNG seed is changed by the registered parallel backend (default=FALSE). Set it to 'TRUE' if you know that running your backend will change the RNG state and want to disable the warning. This option can also be set to a character vector that specifies the name(s) of the backend(s) for which the warning should be skipped.

See Also

foreach, doParallel, registerDoParallel, doMPI

Examples

if (requireNamespace("doParallel", quietly = TRUE)) {
  cl <- parallel::makeCluster(2)
  doParallel::registerDoParallel(cl)
  on.exit(parallel::stopCluster(cl), add = TRUE)

  # standard %dopar% loops are _not_ reproducible
  set.seed(1234)
  s1 <- foreach(i=1:4) %dopar% { runif(1) }
  set.seed(1234)
  s2 <- foreach(i=1:4) %dopar% { runif(1) }
  identical(s1, s2)

  # single %dorng% loops are reproducible
  r1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
  r2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
  identical(r1, r2)
  # the sequence of RNG seeds is stored as an attribute
  attr(r1, "rng")
} else {
  message("Package 'doParallel' is not installed; skipping this example.")
}

# More examples can be found in demo `doRNG`
## Not run: 
demo('doRNG')

## End(Not run)

## Some features of the %dorng% foreach operator 
if (requireNamespace("doParallel", quietly = TRUE)) {
  ## Fork backend on Unix
  if (.Platform$OS.type == "unix") {
    doParallel::registerDoParallel(2)

    r1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
    r2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
    identical(r1, r2)
    attr(r1, "rng")

    set.seed(1234)
    s1 <- foreach(i=1:4) %dorng% { runif(1) }
    s2 <- foreach(i=1:4) %dorng% { runif(1) }
    identical(s1, s2)

    set.seed(1234)
    s1.2 <- foreach(i=1:4) %dorng% { runif(1) }
    s2.2 <- foreach(i=1:4) %dorng% { runif(1) }
    identical(s1, s1.2) && identical(s2, s2.2)
    identical(r1, s1)
  }

  ## PSOCK cluster (works everywhere)
  cl <- parallel::makeCluster(2)
  doParallel::registerDoParallel(cl)
  on.exit(parallel::stopCluster(cl), add = TRUE)

  s1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
  s2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
  identical(s1, s2)

  registerDoSEQ()
} else {
  message("Package 'doParallel' is not installed; skipping these examples.")
}

## Not run: 
# MPI cluster (requires a working MPI + Rmpi setup)
library(doMPI)
cl <- startMPIcluster(2)
registerDoMPI(cl)

s1 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
s2 <- foreach(i=1:4, .options.RNG=1234) %dorng% { runif(1) }
identical(s1, s2)

closeCluster(cl)
registerDoSEQ()

## End(Not run)

doRNG documentation built on Feb. 5, 2026, 5:08 p.m.