makeCluster:

Description

Creates a set of copies of R running in parallel and communicating over sockets.

Usage

makeCluster(spec, type, ...)
makePSOCKcluster(names, ...)
makeForkCluster(nnodes = getOption("mc.cores", 2L), ...)
stopCluster(cl = NULL)
setDefaultCluster(cl = NULL)

Arguments

spec

A specification appropriate to the type of cluster.

names

Either a character vector of host names on which to run the worker copies of R, or a positive integer (in which case that number of copies is run on localhost).

nnodes

The number of nodes to be forked.

type

One of the supported types: see ‘Details’.

…

Options to be passed to the function spawning the workers. See ‘Details’.

an object of class "cluster".

Value

An object of class c("SOCKcluster", "cluster").

Details

makeCluster creates a cluster of one of the supported types. The default type, "PSOCK", calls makePSOCKcluster. Type "FORK" calls makeForkCluster. Other types are passed to package https://CRAN.R-project.org/package=snow. makePSOCKcluster is an enhanced version of makeSOCKcluster in package https://CRAN.R-project.org/package=snow. It runs Rscript on the specified host(s) to set up a worker process which listens on a socket for expressions to evaluate, and returns the results (as serialized objects). makeForkCluster is merely a stub on Windows. On Unix-alike platforms it creates the worker process by forking. The workers are most often running on the same host as the master, when no options need be set. Several options are supported (mainly for makePSOCKcluster):

master: The host name of the master, as known to the workers. This may not be the same as it is known to the master, and on private subnets it may be necessary to specify this as a numeric IP address. For example, macOS is likely to detect a machine as somename.local, a name known only to itself.
port: The port number for the socket connection, default taken from the environment variable R_PARALLEL_PORT, then a randomly chosen port in the range 11000:11999.
timeout: The timeout in seconds for that port. Default 30 days (and the POSIX standard only requires values up to 31 days to be supported).
outfile: Where to direct the stdout and stderr connection output from the workers. "" indicates no redirection (which may only be useful for workers on the local machine). Defaults to /dev/null (nul: on Windows). The other possibility is a file path on the worker's host. Files will be opened in append mode, as all workers log to the same file.
homogeneous: Logical. Are all the hosts running identical setups, so Rscript can be launched using the same path on each? Otherwise Rscript has to be in the default path on the workers.
rscript: The path to Rscript on the workers, used if homogeneous is true. Defaults to the full path on the master.
rscript_args: Character vector of additional arguments for Rscript such as --no-environ.
renice: A numerical ‘niceness’ to set for the worker processes, e.g. 15 for a low priority. OS-dependent: see psnice for details.
rshcmd: The command to be run on the master to launch a process on another host. Defaults to ssh.
user: The user name to be used when communicating with another host.
manual: Logical. If true the workers will need to be run manually.
methods: Logical. If true (default) the workers will load the methods package: not loading it saves ca 30% of the startup CPU time of the cluster.
useXDR: Logical. If true (default) serialization will use XDR: where large amounts of data are to be transferred and all the nodes are little-endian, communication may be substantially faster if this is set to false.

Function makeForkCluster creates a socket cluster by forking (and hence is not available on Windows). It supports options port, timeout and outfile, and always uses useXDR = FALSE. It is good practice to shut down the workers by calling stopCluster: however the workers will terminate themselves once the socket on which they are listening for commands becomes unavailable, which it should if the master R session is completed (or its process dies). Function setDefaultCluster registers a cluster as the default one for the current session. Using setDefaultCluster(NULL) removes the registered cluster, as does stopping that cluster.