Create a cluster future whose value will be resolved asynchronously in a parallel process

WARNING: This function must never be called. It may only be used with plan()

cluster(
  ...,
  workers = availableWorkers(constraints = "connections"),
  gc = FALSE,
  earlySignal = FALSE,
  persistent = FALSE,
  envir = parent.frame()
)

Arguments

workers

A cluster object, a character vector of host names, a positive numeric scalar, or a function. If a character vector or a numeric scalar, a cluster object is created using makeClusterPSOCK(workers). If a function, it is called without arguments when the future is created and its value is used to configure the workers. The function should return any of the above types.

gc

If TRUE, the garbage collector run (in the process that evaluated the future) only after the value of the future is collected. Exactly when the values are collected may depend on various factors such as number of free workers and whether earlySignal is TRUE (more frequently) or FALSE (less frequently). Some types of futures ignore this argument.

earlySignal

Specified whether conditions should be signaled as soon as possible or not.

persistent

If FALSE, the evaluation environment is cleared from objects prior to the evaluation of the future.

envir

The environment from where global objects should be identified.

...

Additional named elements passed to Future().

Value

A ClusterFuture.

Details

A cluster future is a future that uses cluster evaluation, which means that its value is computed and resolved in parallel in another process.

This function is must not be called directly. Instead, the typical usages are:

# Evaluate futures via a single background R process on the local machine
plan(cluster, workers = I(1))

# Evaluate futures via two background R processes on the local machine
plan(cluster, workers = 2)

# Evaluate futures via a single R process on another machine on on the
# local area network (LAN)
plan(cluster, workers = "raspberry-pi")

# Evaluate futures via a single R process running on a remote machine
plan(cluster, workers = "pi.example.org")

# Evaluate futures via four R processes, one running on the local machine,
# two running on LAN machine 'n1' and one on a remote machine
plan(cluster, workers = c("localhost", "n1", "n1", "pi.example.org"))

See also

For alternative future backends, see the 'A Future for R: Available Future Backends' vignette and https://www.futureverse.org/backends.html.

Examples

# \donttest{

## Use cluster futures
cl <- parallel::makeCluster(2, timeout = 60)
plan(cluster, workers = cl)

## A global variable
a <- 0

## Create future (explicitly)
f <- future({
  b <- 3
  c <- 2
  a * b * c
})

## A cluster future is evaluated in a separate process.
## Regardless, changing the value of a global variable will
## not affect the result of the future.
a <- 7
print(a)
#> [1] 7

v <- value(f)
print(v)
#> [1] 0
stopifnot(v == 0)

## CLEANUP
parallel::stopCluster(cl)

# }