R: Create a cluster future whose value will be resolved...

cluster {future} | R Documentation

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

### Description

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

### Usage

    cluster(expr, envir = parent.frame(), substitute = TRUE, lazy = FALSE,
      seed = NULL, globals = TRUE, persistent = FALSE,
      workers = availableWorkers(), user = NULL, revtunnel = TRUE,
      homogeneous = TRUE, gc = FALSE, earlySignal = FALSE, label = NULL,
      ...)

### Arguments

`expr` | An R expression to be evaluated.
`envir` | The environment from where global objects should be identified. Depending on the future strategy (the `evaluator`), it may also be the environment in which the expression is evaluated.
`substitute` | If TRUE, argument `expr` is `substitute()`:ed, otherwise not.
`lazy` | Specifies whether a future should be resolved lazily or eagerly (default).
`seed` | (optional) A L'Ecuyer-CMRG RNG seed.
`globals` | (optional) A logical, a character vector, or a named list for controlling how globals are handled. For details, see below section.
`persistent` | If FALSE, the evaluation environment is cleared from objects prior to the evaluation of the future.
`workers` | A cluster object created by `makeCluster()`.
`user` | (optional) The user name to be used when communicating with another host.
`revtunnel` | If TRUE, reverse SSH tunneling is used for the PSOCK cluster nodes to connect back to the master R process. This avoids the hassle of firewalls, port forwarding and having to know the internal / public IP address of the master R session.
`homogeneous` | If TRUE, all cluster nodes is assumed to use the same path to ‘Rscript’ as the main R session. If FALSE, the it is assumed to be on the PATH for each node.
`gc` | If TRUE, the garbage collector run (in the process that evaluated the future) after the value of the future is collected.
`earlySignal` | Specified whether conditions should be signaled as soon as possible or not.
`label` | An optional character string label attached to the future.
`...` | Additional arguments passed to the "evaluator".

### Details

This function will block if all available R cluster nodes are occupied and will be unblocked as soon as one of the already running cluster futures is resolved.

The preferred way to create an cluster future is not to call this function directly, but to register it via `plan(cluster)` such that it becomes the default mechanism for all futures. After this `future()` and `%<-%` will create cluster futures.

### Value

A ClusterFuture.

### Examples

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

    ## A global variable
    a <- 0

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

    ## A cluster future is evaluated in a separate process.
    ## Changing the value of a global variable will not
    ## affect the result of the future.
    a <- 7
    print(a)

    v <- value(f)
    print(v)
    stopifnot(v == 0)

    ## CLEANUP
    parallel::stopCluster(cl)

[Package future version 1.8.0 Index]