% Generated by roxygen2: do not edit by hand
% Please edit documentation in R/makeClusterPSOCK.R, R/makeNodePSOCK.R,
%   R/makeZZZ.R
\name{makeClusterPSOCK}
\alias{makeClusterPSOCK}
\alias{PSOCK}
\alias{makeNodePSOCK}
\title{Create a PSOCK Cluster of R Workers for Parallel Processing}
\usage{
makeClusterPSOCK(
  workers,
  makeNode = makeNodePSOCK,
  port = c("auto", "random"),
  user = NULL,
  ...,
  autoStop = FALSE,
  tries = getOption2("parallelly.makeNodePSOCK.tries", 3L),
  delay = getOption2("parallelly.makeNodePSOCK.tries.delay", 15),
  validate = getOption2("parallelly.makeNodePSOCK.validate", TRUE),
  verbose = getOption2("parallelly.debug", FALSE)
)

makeNodePSOCK(
  worker = getOption2("parallelly.localhost.hostname", "localhost"),
  master = NULL,
  port,
  connectTimeout = getOption2("parallelly.makeNodePSOCK.connectTimeout", 2 * 60),
  timeout = getOption2("parallelly.makeNodePSOCK.timeout", 30 * 24 * 60 * 60),
  rscript = NULL,
  homogeneous = NULL,
  rscript_args = NULL,
  rscript_envs = NULL,
  rscript_libs = NULL,
  rscript_startup = NULL,
  rscript_sh = c("auto", "cmd", "sh", "none"),
  default_packages = c("datasets", "utils", "grDevices", "graphics", "stats", if
    (methods) "methods"),
  methods = TRUE,
  socketOptions = getOption2("parallelly.makeNodePSOCK.socketOptions", "no-delay"),
  useXDR = getOption2("parallelly.makeNodePSOCK.useXDR", FALSE),
  outfile = "/dev/null",
  renice = NA_integer_,
  rshcmd = getOption2("parallelly.makeNodePSOCK.rshcmd", NULL),
  user = NULL,
  revtunnel = NA,
  rshlogfile = NULL,
  rshopts = getOption2("parallelly.makeNodePSOCK.rshopts", NULL),
  rank = 1L,
  manual = FALSE,
  dryrun = FALSE,
  quiet = FALSE,
  setup_strategy = getOption2("parallelly.makeNodePSOCK.setup_strategy", "parallel"),
  action = c("launch", "options"),
  verbose = FALSE
)
}
\arguments{
\item{workers}{The hostnames of workers (as a character vector) or the
number of localhost workers (as a positive integer).}

\item{makeNode}{A function that creates a \code{"SOCKnode"} or
\code{"SOCK0node"} object, which represents a connection to a worker.}

\item{port}{The port number of the master used for communicating with all
the workers (via socket connections).  If an integer vector of ports, then
a random one among those is chosen.  If \code{"random"}, then a random port in
is chosen from \code{11000:11999}, or from the range specified by
environment variable \env{R_PARALLELLY_RANDOM_PORTS}.
If \code{"auto"} (default), then the default (single) port is taken from
environment variable \env{R_PARALLEL_PORT}, otherwise \code{"random"} is
used.
\emph{Note, do not use this argument to specify the port number used by
\code{rshcmd}, which typically is an SSH client.  Instead, if the SSH daemon
runs on a different port than the default 22, specify the SSH port by
appending it to the hostname, e.g. \code{"remote.server.org:2200"} or via
SSH options \option{-p}, e.g. \code{rshopts = c("-p", "2200")}.}}

\item{user}{(optional) The user name to be used when communicating with
another host.}

\item{\dots}{Optional arguments passed to
\code{makeNode(workers[i], ..., rank = i)} where \code{i = seq_along(workers)}.}

\item{autoStop}{If TRUE, the cluster will be automatically stopped
using \code{\link[parallel:makeCluster]{stopCluster}()} when it is
garbage collected, unless already stopped.  See also \code{\link[=autoStopCluster]{autoStopCluster()}}.}

\item{tries, delay}{Maximum number of attempts done to launch each node
with \code{makeNode()} and the delay (in seconds) in-between attempts.
If argument \code{port} specifies more than one port, e.g. \code{port = "random"}
then a random port will be drawn and validated at most \code{tries} times.
Arguments \code{tries} and \code{delay} are used only when
\code{setup_strategy == "sequential"}.}

\item{validate}{If TRUE (default), after the nodes have been created,
they are all validated that they work by inquiring about their session
information, which is saved in attribute \code{session_info} of each node.}

\item{verbose}{If TRUE, informative messages are outputted.}

\item{worker}{The hostname or IP number of the machine where the worker
should run.
Attribute \code{localhost} can be set to TRUE or FALSE to manually indicate
whether \code{worker} is the same as the local host.}

\item{master}{The hostname or IP number of the master / calling machine, as
known to the workers.  If NULL (default), then the default is
\code{Sys.info()[["nodename"]]} unless \code{worker} is \emph{localhost} or
\code{revtunnel = TRUE} in case it is \code{"localhost"}.}

\item{connectTimeout}{The maximum time (in seconds) allowed for each socket
connection between the master and a worker to be established (defaults to
2 minutes). \emph{See note below on current lack of support on Linux and
macOS systems.}}

\item{timeout}{The maximum time (in seconds) allowed to pass without the
master and a worker communicate with each other (defaults to 30 days).}

\item{rscript, homogeneous}{The system command for launching \command{Rscript}
on the worker and whether it is installed in the same path as the calling
machine or not.  For more details, see below.}

\item{rscript_args}{Additional arguments to \command{Rscript} (as a character
vector).  This argument can be used to customize the \R environment of the
workers before they launches.
For instance, use \code{rscript_args = c("-e", shQuote('setwd("/path/to")'))}
to set the working directory to \file{/path/to} on \emph{all} workers.}

\item{rscript_envs}{A named character vector environment variables to
set or unset on worker at startup, e.g.
\code{rscript_envs = c(FOO = "3.14", "HOME", "UNKNOWN", UNSETME = NA_character_)}.
If an element is not named, then the value of that variable will be used as
the name and the value will be the value of \code{Sys.getenv()} for that
variable.  Non-existing environment variables will be dropped.
These variables are set using \code{Sys.setenv()}.
An named element with value \code{NA_character_} will cause that variable to be
unset, which is done via \code{Sys.unsetenv()}.}

\item{rscript_libs}{A character vector of \R library paths that will be
used for the library search path of the \R workers.  An asterisk
(\code{"*"}) will be resolved to the default \code{.libPaths()} \emph{on the
worker}. That is, to \code{prepend} a folder, instead of replacing the
existing ones, use \code{rscript_libs = c("new_folder", "*")}.
To pass down a non-default library path currently set \emph{on the main \R
session} to the workers, use \code{rscript_libs = .libPaths()}.}

\item{rscript_startup}{An \R expression or a character vector of \R code,
or a list with a mix of these, that will be evaluated on the \R worker
prior to launching the worker's event loop.
For instance, use \code{rscript_startup = 'setwd("/path/to")'}
to set the working directory to \file{/path/to} on \emph{all} workers.}

\item{rscript_sh}{The type of shell used where \code{rscript} is launched,
which should be \code{"sh"} is launched via a POSIX shell and \code{"cmd"} if
launched via an MS Windows shell.  This controls how shell command-line
options are quoted, but also how R string expression are quoted when
passed to \code{Rscript}.
If \code{"none"}, then no quoting is done.
If \code{"auto"} (default), and the cluster node is launched locally, then it
is set to \code{"sh"} or \code{"cmd"} according to the current platform.
\emph{If launched remotely}, then it is set to \code{"sh"} based on the assumption
remote machines typically launch commands via SSH in a POSIX shell.
If the remote machines run MS Windows, use \code{rscript_sh = "cmd"}.
If \code{length(rscript_sh)} is two, then \code{rscript_sh[1]} is for the inner and
\code{rscript_sh[2]} is for the outer shell quoting of the Rscript call.
More precisely, \code{rscript_sh[1]} is for Rscript arguments that need shell
quoting (e.g. \verb{Rscript -e "<expr>"}), and \code{rscript_sh[2]} is for the whole
\verb{Rscript ...} call.
If \code{length(rscript_sh)} is one, then it is used for both the inner and the
outer shell quoting.}

\item{default_packages}{A character vector or NULL that controls which R
packages are attached on each cluster node during startup.  An asterisk
(\code{"*"}) resolves to \code{getOption("defaultPackages")} \emph{on the current machine}.
If NULL, then the default set of packages R are attached.}

\item{methods}{If TRUE (default), then the \pkg{methods} package is also
loaded. This is argument exists for legacy reasons due to how
\command{Rscript} worked in R (< 3.5.0).}

\item{socketOptions}{A character string that sets \R option
\code{socketOptions} on the worker.}

\item{useXDR}{If FALSE (default), the communication between master and workers, which is binary, will use small-endian (faster), otherwise big-endian ("XDR"; slower).}

\item{outfile}{Where to direct the \link[base:showConnections]{stdout} and
\link[base:showConnections]{stderr} connection output from the workers.
If NULL, then no redirection of output is done, which means that the
output is relayed in the terminal on the local computer.  On Windows, the
output is only relayed when running \R from a terminal but not from a GUI.}

\item{renice}{A numerical 'niceness' (priority) to set for the worker
processes.}

\item{rshcmd, rshopts}{The command (character vector) to be run on the master
to launch a process on another host and any additional arguments (character
vector).  These arguments are only applied if \code{machine} is not
\emph{localhost}.  For more details, see below.}

\item{revtunnel}{If TRUE, a reverse SSH tunnel is set up for each worker such
that the worker \R process sets up a socket connection to its local port
\code{(port + rank - 1)} which then reaches the master on port \code{port}.
If FALSE, then the worker will try to connect directly to port \code{port} on
\code{master}.
If NA, then TRUE or FALSE is inferred from inspection of \code{rshcmd[1]}.
For more details, see below.}

\item{rshlogfile}{(optional) If a filename, the output produced by the
\code{rshcmd} call is logged to this file, of if TRUE, then it is logged
to a temporary file.  The log file name is available as an attribute
as part of the return node object.
\emph{Warning: This only works with SSH clients that support command-line
option \option{-E out.log`}}.  For example, PuTTY's \command{plink} does
\emph{not} support this option, and any attempts to specify \code{rshlogfile} will
cause the SSH connection to fail.}

\item{rank}{A unique one-based index for each worker (automatically set).}

\item{manual}{If TRUE the workers will need to be run manually. The command
to run will be displayed.}

\item{dryrun}{If TRUE, nothing is set up, but a message suggesting how to
launch the worker from the terminal is outputted.  This is useful for
troubleshooting.}

\item{quiet}{If TRUE, then no output will be produced other than that from
using \code{verbose = TRUE}.}

\item{setup_strategy}{If \code{"parallel"} (default), the workers are set up
concurrently, one after the other.  If \code{"sequential"}, they are set up
sequentially.}

\item{action}{This is an internal argument.}
}
\value{
An object of class \code{c("RichSOCKcluster", "SOCKcluster", "cluster")}
consisting of a list of \code{"SOCKnode"} or \code{"SOCK0node"} workers (that also
inherit from \code{RichSOCKnode}).

\code{makeNodePSOCK()} returns a \code{"SOCKnode"} or
\code{"SOCK0node"} object representing an established connection to a worker.
}
\description{
The \code{makeClusterPSOCK()} function creates a cluster of \R workers
for parallel processing.  These \R workers may be background \R sessions
on the current machine, \R sessions on external machines (local or remote),
or a mix of such. For external workers, the default is to use SSH to
connect to those external machines.  This function works similarly to
\code{\link[parallel:makeCluster]{makePSOCKcluster}()} of the
\pkg{parallel} package, but provides additional and more flexibility
options for controlling the setup of the system calls that launch the
background \R workers, and how to connect to external machines.
}
\section{Alternative usage}{

In R (>= 4.5.0), an alternatively to using
\code{cl <- parallelly::makeClusterPSOCK(workers)} is:

\if{html}{\out{<div class="sourceCode">}}\preformatted{cl <- parallel::makeCluster(workers, type = parallelly::PSOCK)
}\if{html}{\out{</div>}}
}

\section{Protection against CPU overuse}{

Using too many parallel workers on the same machine may result in
overusing the CPU.  For example, if an R script hard codes the
number of parallel workers to 32, as in

\if{html}{\out{<div class="sourceCode r">}}\preformatted{cl <- makeClusterPSOCK(32)
}\if{html}{\out{</div>}}

it will use more than 100\% of the CPU cores when running on machine with
fewer than 32 CPU cores.  For example, on a eight-core machine, this
may run the CPU at 400\% of its capacity, which has a significant
negative effect on the current R process, but also on all other processes
running on the same machine.  This also a problem on systems where R
gets allotted a specific number of CPU cores, which is the case on
high-performance compute (HPC) clusters, but also on other shared systems
that limits user processes via Linux Control Groups (cgroups).
For example, a free account on Posit Cloud is limited to a single
CPU core. Parallelizing with 32 workers when only having access to
a single core, will result in 3200\% overuse and 32 concurrent R
processes competing for this single CPU core.

To protect against CPU overuse by mistake, \code{makeClusterPSOCK()} will
warn when parallelizing above 100\%;

\if{html}{\out{<div class="sourceCode r">}}\preformatted{cl <- parallelly::makeClusterPSOCK(12, dryrun = TRUE)
Warning message:
In checkNumberOfLocalWorkers(workers) :
  Careful, you are setting up 12 localhost parallel workers with
only 8 CPU cores available for this R process, which could result
in a 150\% load. The maximum is set to 100\%. Overusing the CPUs has
negative impact on the current R process, but also on all other
processes of yours and others running on the same machine. See
help("parallelly.options", package = "parallelly") for how to
override this threshold
}\if{html}{\out{</div>}}

Any attempts resulting in more than 300\% overuse will be refused;

\if{html}{\out{<div class="sourceCode r">}}\preformatted{> cl <- parallelly::makeClusterPSOCK(25, dryrun = TRUE)
Error in checkNumberOfLocalWorkers(workers) : 
  Attempting to set up 25 localhost parallel workers with only
8 CPU cores available for this R process, which could result in
a 312\% load. The maximum is set to 300\%. Overusing the CPUs has
negative impact on the current R process, but also on all other
processes of yours and others running on the same machine. See
help("parallelly.options", package = "parallelly") for how to
override this threshold
}\if{html}{\out{</div>}}

See \link{parallelly.options} for how to change the default thresholds.
}

\section{Definition of \emph{localhost}}{

A hostname is considered to be \emph{localhost} if it equals:
\itemize{
\item \code{"localhost"},
\item \code{"127.0.0.1"}, or
\item \code{Sys.info()[["nodename"]]}.
}
It is also considered \emph{localhost} if it appears on the same line
as the value of \code{Sys.info()[["nodename"]]} in file \file{/etc/hosts}.
}

\section{Default SSH client and options (arguments \code{rshcmd} and \code{rshopts})}{

Arguments \code{rshcmd} and \code{rshopts} are only used when connecting
to an external host.

The default method for connecting to an external host is via SSH and the
system executable for this is given by argument \code{rshcmd}.  The default
is given by option
\code{\link[=parallelly.options]{parallelly.makeNodePSOCK.rshcmd}}.
If that is not
set, then the default is to use \command{ssh} on Unix-like systems,
including macOS as well as Windows 10.  On older MS Windows versions, which
does not have a built-in \command{ssh} client, the default is to use
(i) \command{plink} from the \href{https://www.putty.org/}{\command{PuTTY}}
project, and then (ii) the \command{ssh} client that is distributed with
RStudio.

PuTTY puts itself on Windows' system \env{PATH} when installed, meaning this
function will find PuTTY automatically if installed.  If not, to manually
set specify PuTTY as the SSH client, specify the absolute pathname of
\file{plink.exe} in the first element and option \command{-ssh} in the
second as in \code{rshcmd = c("C:/Path/PuTTY/plink.exe", "-ssh")}.
This is because all elements of \code{rshcmd} are individually "shell"
quoted and element \code{rshcmd[1]} must be on the system \env{PATH}.

Furthermore, when running \R from RStudio on Windows, the \command{ssh}
client that is distributed with RStudio will also be considered.
This client, which is from \href{https://en.wikipedia.org/wiki/MinGW}{MinGW}
MSYS, is searched for in the folder given by the \env{RSTUDIO_MSYS_SSH}
environment variable---a variable that is (only) set when running RStudio.
To use this SSH client outside of RStudio, set \env{RSTUDIO_MSYS_SSH}
accordingly.

You can override the default set of SSH clients that are searched for
by specifying them in argument \code{rshcmd} or via option
\code{\link[=parallelly.options]{parallelly.makeNodePSOCK.rshcmd}}
using the format \verb{<...>}, e.g.
\code{rshcmd = c("<rstudio-ssh>", "<putty-plink>", "<ssh>")}.  See
below for examples.

If no SSH-client is found, an informative error message is produced.

Additional SSH command-line options may be specified via argument \code{rshopts},
which defaults to option \code{parallelly.makeNodePSOCK.rshopts}. For
instance, a private SSH key can be provided as
\code{rshopts = c("-i", "~/.ssh/my_private_key")}.  PuTTY users should
specify a PuTTY PPK file, e.g.
\code{rshopts = c("-i", "C:/Users/joe/.ssh/my_keys.ppk")}.
Contrary to \code{rshcmd}, elements of \code{rshopts} are not quoted.
}

\section{Accessing external machines that prompts for a password}{

\emph{IMPORTANT: With one exception, it is not possible to for these
functions to log in and launch \R workers on external machines that requires
a password to be entered manually for authentication.}
The only known exception is the PuTTY client on Windows for which one can
pass the password via command-line option \option{-pw}, e.g.
\code{rshopts = c("-pw", "MySecretPassword")}.

Note, depending on whether you run \R in a terminal or via a GUI, you might
not even see the password prompt.  It is also likely that you cannot enter
a password, because the connection is set up via a background system call.

The poor man's workaround for setup that requires a password is to manually
log into the each of the external machines and launch the \R workers by hand.
For this approach, use \code{manual = TRUE} and follow the instructions
which include cut'n'pasteable commands on how to launch the worker from the
external machine.

However, a much more convenient and less tedious method is to set up
key-based SSH authentication between your local machine and the external
machine(s), as explain below.
}

\section{Accessing external machines via key-based SSH authentication}{

The best approach to automatically launch \R workers on external machines
over SSH is to set up key-based SSH authentication.  This will allow you
to log into the external machine without have to enter a password.

Key-based SSH authentication is taken care of by the SSH client and not \R.
To configure this, see the manuals of your SSH client or search the web
for "ssh key authentication".
}

\section{Reverse SSH tunneling}{

If SSH is used, which is inferred from \code{rshcmd[1]}, then the default is
to use reverse SSH tunneling (\code{revtunnel = TRUE}), otherwise not
(\code{revtunnel = FALSE}). Using reverse SSH tunneling, avoids complications
from otherwise having to configure port forwarding in firewalls, which
often requires static IP address as well as privileges to edit the
firewall on your outgoing router, something most users don't have.
It also has the advantage of not having to know the internal and / or the
public IP address / hostname of the master.
Yet another advantage is that there will be no need for a DNS lookup by the
worker machines to the master, which may not be configured or is disabled
on some systems, e.g. compute clusters.
}

\section{Argument \code{rscript}}{

If \code{homogeneous} is FALSE, the \code{rscript} defaults to \code{"Rscript"}, i.e. it
is assumed that the \command{Rscript} executable is available on the
\env{PATH} of the worker.
If \code{homogeneous} is TRUE, the \code{rscript} defaults to
\code{file.path(R.home("bin"), "Rscript")}, i.e. it is basically assumed that
the worker and the caller share the same file system and \R installation.

When specified, argument \code{rscript} should be a character vector with one or
more elements.  Any asterisk (\code{"*"}) will be resolved to the above default
\code{homogeneous}-dependent \code{Rscript} path.
All elements are automatically shell quoted using \code{\link[base:shQuote]{base::shQuote()}}, except
those that are of format \verb{<ENVVAR>=<VALUE>}, that is, the ones matching the
regular expression '\samp{^[[:alpha:]_][[:alnum:]_]*=.*}'.
Another exception is when \code{rscript} inherits from 'AsIs'.
}

\section{Default value of argument \code{homogeneous}}{

The default value of \code{homogeneous} is TRUE if and only if either
of the following is fulfilled:
\itemize{
\item \code{worker} is \emph{localhost}
\item \code{revtunnel} is FALSE and \code{master} is \emph{localhost}
\item \code{worker} is neither an IP number nor a fully qualified domain
name (FQDN).  A hostname is considered to be a FQDN if it contains
one or more periods
}
In all other cases, \code{homogeneous} defaults to FALSE.
}

\section{Connection timeout}{

Argument \code{connectTimeout} does \emph{not} work properly on Unix and
macOS due to limitation in \R itself.  For more details on this, please see
R-devel thread 'BUG?: On Linux setTimeLimit() fails to propagate timeout
error when it occurs (works on Windows)' on 2016-10-26
(\url{https://stat.ethz.ch/pipermail/r-devel/2016-October/073309.html}).
When used, the timeout will eventually trigger an error, but it won't happen
until the socket connection timeout \code{timeout} itself happens.
}

\section{Communication timeout}{

If there is no communication between the master and a worker within the
\code{timeout} limit, then the corresponding socket connection will be
closed automatically.  This will eventually result in an error in code
trying to access the connection.
This timeout is also what terminates a stray-running parallel cluster-node
process.
}

\section{Failing to set up local workers}{

When setting up a cluster of localhost workers, that is, workers running
on the same machine as the master \R process, occasionally a connection
to a worker ("cluster node") may fail to be set up.
When this occurs, an informative error message with troubleshooting
suggestions will be produced.
The most common reason for such localhost failures is due to port
clashes.  Retrying will often resolve the problem.

If R stalls when setting up a cluster of local workers, then it might
be that you have a virtual private network (VPN) enabled that is
configured to prevent you from connecting to \code{localhost}.  To verify that
this is the case, call the following from the terminal:

\if{html}{\out{<div class="sourceCode sh">}}\preformatted{\{local\}$ ssh localhost "date"
}\if{html}{\out{</div>}}

This also freezed if the VPN intercepts connections to \code{localhost}.
If this happens, try also:

\if{html}{\out{<div class="sourceCode sh">}}\preformatted{\{local\}$ ssh 127.0.0.1 "date"
}\if{html}{\out{</div>}}

In rare cases, \verb{127.0.0.1} might work when \code{localhost} does not.
If the latter works, setting R option:

\if{html}{\out{<div class="sourceCode r">}}\preformatted{options(parallelly.localhost.hostname = "127.0.0.1")
}\if{html}{\out{</div>}}

should solve it (the default is \code{"localhost"}).  You can set this
automatically when R starts by adding it to your \verb{~/.Rprofile} startup
file. Alternatively, set environment variable
\verb{R_PARALLELLY_LOCALHOST_HOSTNAME=127.0.0.1} in your \verb{~/.Renviron} file.

If using \verb{127.0.0.1} did not work around the problem, check your VPN
settings and make sure it allows connections to \code{localhost} or \verb{127.0.0.1}.
}

\section{Failing to set up remote workers}{

A cluster of remote workers runs \R processes on external machines. These
external \R processes are launched over, typically, SSH to the remote
machine.  For this to work, each of the remote machines needs to have
\R installed, which preferably is of the same version as what is on the
main machine.  For this to work, it is required that one can SSH to the
remote machines.  Ideally, the SSH connections use authentication based
on public-private SSH keys such that the set up of the remote workers can
be fully automated (see above).  If \code{makeClusterPSOCK()} fails to set
up one or more remote \R workers, then an informative error message is
produced.
There are a few reasons for failing to set up remote workers.  If this
happens, start by asserting that you can SSH to the remote machine and
launch \file{Rscript} by calling something like:
\preformatted{
{local}$ ssh -l alice remote.server.org
{remote}$ Rscript --version
R scripting front-end version 4.2.2 (2022-10-31)
{remote}$ logout
{local}$
}
When you have confirmed the above to work, then confirm that you can achieve
the same in a single command-line call;
\preformatted{
{local}$ ssh -l alice remote.server.org Rscript --version
R scripting front-end version 4.2.2 (2022-10-31)
{local}$
}
The latter will assert that you have proper startup configuration also for
\emph{non-interactive} shell sessions on the remote machine.

If the remote machines are running on MS Windows, make sure to add argument
\code{rscript_sh = "cmd"} when calling \code{makeClusterPSOCK()}, because the default
is \code{rscript_sh = "sh"}, which assumes that that the remote machines are
Unix-like machines.

Another reason for failing to setup remote workers could be that they are
running an \R version that is not compatible with the version that your main
\R session is running.  For instance, if we run R (>= 3.6.0) locally and the
workers run R (< 3.5.0), we will get:
\verb{Error in unserialize(node$con) : error reading from connection}.
This is because R (>= 3.6.0) uses serialization format version 3 by default
whereas R (< 3.5.0) only supports version 2.  We can see the version of the
\R workers by adding \code{rscript_args = c("-e", shQuote("getRversion()"))} when
calling \code{makeClusterPSOCK()}.
}

\section{For package developers}{

When creating a \code{cluster} object, for instance via \code{parallel::makeCluster()}
or \code{parallelly::makeClusterPSOCK()}, in a package help example, in a package
vignette, or in a package test, we must \emph{remember to stop the cluster at
the end of all examples(*), vignettes, and unit tests}. This is required in
order to not leave behind stray parallel \code{cluster} workers after our main R
session terminates. On Linux and macOS, the operating system often takes
care of terminating the worker processes if we forget, but on MS Windows
such processes will keep running in the background until they time out
themselves, which takes 30 days (sic!).

\verb{R CMD check --as-cran} will indirectly detect these stray worker processes
on MS Windows when running R (>= 4.3.0). They are detected, because they
result in placeholder \verb{Rscript<hexcode>} files being left behind in
the temporary directory.  The check NOTE to look out for
(only in R (>= 4.3.0)) is:

\if{html}{\out{<div class="sourceCode">}}\preformatted{* checking for detritus in the temp directory ... NOTE
Found the following files/directories:
  'Rscript1058267d0c10' 'Rscriptbd4267d0c10'
}\if{html}{\out{</div>}}

Those \verb{Rscript<hexcode>} files are from background R worker processes,
which almost always are parallel \code{cluster}:s that we forgot to stop
at the end.  To stop all \code{cluster} workers, use \code{\link[parallel:makeCluster]{parallel::stopCluster()}}
at the end of your examples(*), vignettes, and package tests for every
\code{cluster} object that is created.

(*) Currently, examples are excluded from the detritus checks.
This was validated with R-devel revision 82991 (2022-10-02).
}

\examples{
## NOTE: Drop 'dryrun = TRUE' below in order to actually connect.  Add
## 'verbose = TRUE' if you run into problems and need to troubleshoot.

## ---------------------------------------------------------------
## Section 1. Setting up parallel workers on the local machine
## ---------------------------------------------------------------
## EXAMPLE: Two workers on the local machine
workers <- c("localhost", "localhost")
cl <- makeClusterPSOCK(workers, dryrun = TRUE, quiet = TRUE)


## EXAMPLE: Launch 124 workers on MS Windows 10, where half are
## running on CPU Group #0 and half on CPU Group #1.  
## (https://lovickconsulting.com/2021/11/18/
##  running-r-clusters-on-an-amd-threadripper-3990x-in-windows-10-2/)
## The parallel workers are launched as:
## "\%COMSPEC\%" /c start /B /NODE 1 /AFFINITY 0xFFFFFFFFFFFFFFFE ...
## ...
## "\%COMSPEC\%" /c start /B /NODE 1 /AFFINITY 0xFFFFFFFFFFFFFFFE ...

## Temporarily disable CPU load protection for this example
oopts <- options(parallelly.maxWorkers.localhost = Inf)

ncores <- 124
cpu_groups <- c(0, 1)
cl <- lapply(cpu_groups, FUN = function(cpu_group) {
    parallelly::makeClusterPSOCK(ncores \%/\% length(cpu_groups),
      rscript = I(c(
        Sys.getenv("COMSPEC"), "/c", "start", "/B",
        "/NODE", cpu_group, "/AFFINITY", "0xFFFFFFFFFFFFFFFE",
        "*"
      )),
      dryrun = TRUE, quiet = TRUE
    )
})
## merge the two 62-node clusters into one with 124 nodes
cl <- do.call(c, cl)

## Re-enable CPU load protection
options(oopts)


## ---------------------------------------------------------------
## Section 2. Setting up parallel workers on remote machines
## ---------------------------------------------------------------
## EXAMPLE: Three remote workers
## Setup of three R workers on two remote machines are set up
## The parallel workers are launched as:
## '/usr/bin/ssh' -R 11058:localhost:11058 n1.remote.org ...
## '/usr/bin/ssh' -R 11059:localhost:11058 n2.remote.org ...
## '/usr/bin/ssh' -R 11060:localhost:11058 n1.remote.org ...
workers <- c("n1.remote.org", "n2.remote.org", "n1.remote.org")
cl <- makeClusterPSOCK(workers, dryrun = TRUE, quiet = TRUE)


## EXAMPLE: Two remote workers running on MS Windows.  Because the
## remote workers are MS Windows machines, we need to use
## rscript_sh = "cmd".
## The parallel workers are launched as:
## '/usr/bin/ssh' -R 11912:localhost:11912 mswin1.remote.org ...
## '/usr/bin/ssh' -R 11913:localhost:11912 mswin2.remote.org ...
workers <- c("mswin1.remote.org", "mswin2.remote.org")
cl <- makeClusterPSOCK(workers, rscript_sh = "cmd", dryrun = TRUE, quiet = TRUE)


## EXAMPLE: Local and remote workers
## Same setup when the two machines are on the local network and
## have identical software setups
cl <- makeClusterPSOCK(
  workers,
  revtunnel = FALSE, homogeneous = TRUE,
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Three remote workers 'n1', 'n2', and 'n3' that can only be
## accessed via jumphost 'login.remote.org'
## The parallel workers are launched as:
## '/usr/bin/ssh' -R 11226:localhost:11226 -J login.remote.org n1 ...
## '/usr/bin/ssh' -R 11227:localhost:11226 -J login.remote.org n2 ...
## '/usr/bin/ssh' -R 11228:localhost:11226 -J login.remote.org n1 ...
workers <- c("n1", "n2", "n1")
cl <- makeClusterPSOCK(
  workers,
  rshopts = c("-J", "login.remote.org"),
  homogeneous = FALSE,
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Remote worker running on Linux from MS Windows machine
## Connect to remote Unix machine 'remote.server.org' on port 2200
## as user 'bob' from a MS Windows machine with PuTTY installed.
## Using the explicit special rshcmd = "<putty-plink>", will force
## makeClusterPSOCK() to search for and use the PuTTY plink software,
## preventing it from using other SSH clients on the system search PATH.
## The parallel worker is launched as:
## 'plink' -l bob -P 2200 -i C:/Users/bobby/.ssh/putty.ppk remote.server.org ...
cl <- makeClusterPSOCK(
  "remote.server.org", user = "bob",
  rshcmd = "<putty-plink>",
  rshopts = c("-P", 2200, "-i", "C:/Users/bobby/.ssh/putty.ppk"),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Remote workers with specific setup
## Setup of remote worker with more detailed control on
## authentication and reverse SSH tunneling
## The parallel worker is launched as:
## '/usr/bin/ssh' -l johnny -v -R 11000:gateway:11942 remote.server.org ...
## "R_DEFAULT_PACKAGES=... 'nice' '/path/to/Rscript' --no-init-file ...
cl <- makeClusterPSOCK(
  "remote.server.org", user = "johnny",
  ## Manual configuration of reverse SSH tunneling
  revtunnel = FALSE,
  rshopts = c("-v", "-R 11000:gateway:11942"),
  master = "gateway", port = 11942,
  ## Run Rscript nicely and skip any startup scripts
  rscript = c("nice", "/path/to/Rscript"),
  rscript_args = c("--no-init-file"),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Remote worker running on Linux from RStudio on MS Windows
## Connect to remote Unix machine 'remote.server.org' on port 2200
## as user 'bob' from a MS Windows machine via RStudio's SSH client.
## Using the explicit special rshcmd = "<rstudio-ssh>", will force
## makeClusterPSOCK() to use the SSH client that comes with RStudio,
## preventing it from using other SSH clients on the system search PATH.
## The parallel worker is launched as:
## 'ssh' -l bob remote.server.org:2200 ...
cl <- makeClusterPSOCK(
  "remote.server.org:2200", user = "bob", rshcmd = "<rstudio-ssh>",
  dryrun = TRUE, quiet = TRUE
)


## ---------------------------------------------------------------
## Section 3. Setting up parallel workers on HPC cluster
## ---------------------------------------------------------------
## EXAMPLE: 'Grid Engine' is a high-performance compute (HPC) job
## scheduler where one can request compute resources on multiple nodes,
## each running multiple cores. Examples of Grid Engine schedulers are
## Oracle Grid Engine (formerly Sun Grid Engine), Univa Grid Engine,
## and Son of Grid Engine - all commonly referred to as SGE schedulers.
## Each SGE cluster may have its own configuration with their own way
## of requesting parallel slots. Here are a few examples:
##
##   ## Request 18 slots on a single host
##   qsub -pe smp 18 script.sh
##
##   ## Request 18 slots on one or more hosts
##   qsub -pe mpi 18 script.sh
##
## This will launch the job script 'script.sh' on one host, while have
## reserved in total 18 slots (CPU cores) on this host and possible
## other hosts.
##
## This example shows how to use the SGE command 'qrsh' to launch
## 18 parallel workers from R, which is assumed to have been launched
## by 'script.sh'.
##
## The parallel workers are launched as:
## 'qrsh' -inherit -nostdin -V comphost01 ...
## 'qrsh' -inherit -nostdin -V comphost01 ...
## ...
## 'qrsh' -inherit -nostdin -V comphost06 ...
cl <- makeClusterPSOCK(
  availableWorkers(),
  rshcmd = "qrsh", rshopts = c("-inherit", "-nostdin", "-V"),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: The 'Fujitsu Technical Computing Suite' is a high-performance
## compute (HPC) job scheduler where one can request compute resources on
## multiple nodes, each running multiple cores.  For example,
##
##   pjsub -L vnode=3 -L vnode-core=18 script.sh
##
## reserves 18 cores on three nodes. The job script runs on the first
## with enviroment variables set to infer the other nodes, resulting in
## availableWorkers() to return 3 * 18 workers. When the HPC environment
## does not support SSH between compute nodes, one can use the 'pjrsh'
## command to launch the parallel workers.
##
## The parallel workers are launched as:
## 'pjrsh' comphost01 ...
## 'pjrsh' comphost01 ...
## ...
## 'pjrsh' comphost06 ...
cl <- makeClusterPSOCK(
  availableWorkers(),
  rshcmd = "pjrsh",
  dryrun = TRUE, quiet = TRUE
)



## ---------------------------------------------------------------
## Section 4. Setting up remote parallel workers in the cloud
## ---------------------------------------------------------------
## EXAMPLE: Remote worker running on AWS
## Launching worker on Amazon AWS EC2 running one of the
## Amazon Machine Images (AMI) provided by RStudio
## (https://www.louisaslett.com/RStudio_AMI/)
##
## The parallel worker is launched as:
## '/usr/bin/ssh' -R 11153:localhost:11153 -l ubuntu ...
## -o StrictHostKeyChecking=no -o IdentitiesOnly=yes ...
## -i ~/.ssh/my-private-aws-key.pem 1.2.3.4 ...
public_ip <- "1.2.3.4"
ssh_private_key_file <- "~/.ssh/my-private-aws-key.pem"
cl <- makeClusterPSOCK(
  ## Public IP number of EC2 instance
  public_ip,
  ## User name (always 'ubuntu')
  user = "ubuntu",
  ## Use private SSH key registered with AWS
  rshopts = c(
    "-o", "StrictHostKeyChecking=no",
    "-o", "IdentitiesOnly=yes",
    "-i", ssh_private_key_file
  ),
  ## Set up .libPaths() for the 'ubuntu' user
  ## and then install the future package
  rscript_startup = quote(local({
    p <- Sys.getenv("R_LIBS_USER")
    dir.create(p, recursive = TRUE, showWarnings = FALSE)
    .libPaths(p)
    install.packages("future")
  })),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Remote worker running on GCE
## Launching worker on Google Cloud Engine (GCE) running a
## container based VM (with a #cloud-config specification)
public_ip <- "1.2.3.4"
user <- "johnny"
ssh_private_key_file <- "~/.ssh/google_compute_engine"
cl <- makeClusterPSOCK(
  ## Public IP number of GCE instance
  public_ip,
  ## User name (== SSH key label (sic!))
  user = user,
  ## Use private SSH key registered with GCE
  rshopts = c(
    "-o", "StrictHostKeyChecking=no",
    "-o", "IdentitiesOnly=yes",
    "-i", ssh_private_key_file
  ),
  ## Launch Rscript inside Docker container
  rscript = c(
    "docker", "run", "--net=host", "rocker/r-parallel",
    "Rscript"
  ),
  dryrun = TRUE, quiet = TRUE
)



## ---------------------------------------------------------------
## Section 5. Parallel workers running locally inside virtual
## machines, Linux containers, etc.
## ---------------------------------------------------------------
## EXAMPLE: Two workers limited to 100\% CPU process and 50 MiB of
## memory using Linux CGroups management. The 100\% CPU quota limit
## constrain each worker to use at most one CPU worth of
## processing preventing them from overusing the machine, e.g.
## through unintended nested parallelization. The 50 MiB memory
## limit is strict - if a worker use more than this, the operating
## system will terminate the worker instantly.
## See 'man systemd.resource-control' for more details.
cl <- makeClusterPSOCK(2L,
  rscript = c("systemd-run", "--user", "--scope",
    "-p", "CPUQuota=100\%",
    "-p", "MemoryMax=50M", "-p", "MemorySwapMax=50M",
    "*"
  ),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Two workers running in Docker on the local machine
## Setup of 2 Docker workers running rocker/r-parallel
##
## The parallel workers are launched as:
## R_DEFAULT_PACKAGES=... '/usr/bin/docker' 'run' '--net=host' 'rocker/r-parallel' ...
## R_DEFAULT_PACKAGES=... '/usr/bin/docker' 'run' '--net=host' 'rocker/r-parallel' ...
cl <- makeClusterPSOCK(
  rep("localhost", times = 2L),
  ## Launch Rscript inside Docker container
  rscript = c(
    "docker", "run", "--net=host", "rocker/r-parallel",
    "Rscript"
  ),
  ## IMPORTANT: Because Docker runs inside a virtual machine (VM) on macOS
  ## and MS Windows (not Linux), when the R worker tries to connect back to
  ## the default 'localhost' it will fail, because the main R session is
  ## not running in the VM, but outside on the host.  To reach the host on
  ## macOS and MS Windows, make sure to use master = "host.docker.internal"
  master = if (.Platform$OS.type == "unix") NULL else "host.docker.internal",
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: Two workers running via Linux container 'rocker/r-parallel' from
## DockerHub on the local machine using Apptainer (formerly Singularity)
##
## The parallel workers are launched as:
## R_DEFAULT_PACKAGES=... '/usr/bin/apptainer' 'exec' 'docker://rocker/r-parallel' ...
## R_DEFAULT_PACKAGES=... '/usr/bin/apptainer' 'exec' 'docker://rocker/r-parallel' ...
cl <- makeClusterPSOCK(
  rep("localhost", times = 2L),
  ## Launch Rscript inside Linux container
  rscript = c(
    "apptainer", "exec", "docker://rocker/r-parallel",
    "Rscript"
  ),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: One worker running in udocker on the local machine
## Setup of a single udocker.py worker running rocker/r-parallel
##
## The parallel worker is launched as:
## R_DEFAULT_PACKAGES=... 'udocker.py' 'run' 'rocker/r-parallel' ...
cl <- makeClusterPSOCK(
  "localhost",
  ## Launch Rscript inside Docker container (using udocker)
  rscript = c(
    "udocker.py", "run", "rocker/r-parallel",
    "Rscript"
  ), 
  ## Manually launch parallel workers
  ## (need double shQuote():s because udocker.py drops one level)
  rscript_args = c(
    "-e", shQuote(shQuote("parallel:::.workRSOCK()"))
  ),
  dryrun = TRUE, quiet = TRUE
)


## EXAMPLE: One worker running in Wine for Linux on the local machine
## To install R for MS Windows in Wine, do something like:
##   winecfg  # In GUI, set 'Windows version' to 'Windows 10'
##   wget https://cran.r-project.org/bin/windows/base/R-4.4.2-win.exe
##   wine R-4.4.2-win.exe /SILENT
## Prevent packages from being installed to R's system library:
##   chmod ugo-w "$HOME/.wine/drive_c/Program Files/R/R-4.4.2/library/"
## Verify it works:
##   wine "C:/Program Files/R/R-4.4.2/bin/x64/Rscript.exe" --version
##
## The parallel worker is launched as:
## R_DEFAULT_PACKAGES=... WINEDEBUG=fixme-all R_LIBS_SITE= R_LIBS_USER= 'wine' ...
cl <- makeClusterPSOCK(1L,
  rscript = c(
    ## Silence Wine warnings
    "WINEDEBUG=fixme-all",
    ## Don't pass LC_* and R_LIBS* environments from host to Wine
    sprintf("\%s=", grep("^(LC_|R_LIBS)", names(Sys.getenv()), value = TRUE)),
    "wine",
    "C:/Program Files/R/R-4.4.2/bin/x64/Rscript.exe"
  ),
  dryrun = TRUE, quiet = TRUE
)
}