A cluster future is a future that uses cluster evaluation, which means that its value is computed and resolved in parallel in another process.
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,
...
)
An R expression.
The environment from where global objects should be identified.
If TRUE, argument expr
is
substitute()
:ed, otherwise not.
If FALSE (default), the future is resolved eagerly (starting immediately), otherwise not.
(optional) If TRUE, the random seed, that is, the state of the
random number generator (RNG) will be set such that statistically sound
random numbers are produced (also during parallelization).
If FALSE, it is assumed that the future expression does neither need nor
use random numbers generation.
To use a fixed random seed, specify a L'Ecuyer-CMRG seed (seven integer)
or a regular RNG seed (a single integer).
Furthermore, if FALSE, then the future will be monitored to make sure it
does not use random numbers. If it does and depending on the value of
option future.rng.misUse
, the check is
ignored, an informative warning, or error will be produced.
If seed
is NULL (default), then the effect is as with seed = FALSE
but without the RNG check being performed.
(optional) a logical, a character vector, or a named list
to control how globals are handled.
For details, see section 'Globals used by future expressions'
in the help for future()
.
If FALSE, the evaluation environment is cleared from objects prior to the evaluation of the future.
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.
(optional) The user name to be used when communicating with another host.
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.
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.
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.
Specified whether conditions should be signaled as soon as possible or not.
An optional character string label attached to the future.
Additional named elements passed to ClusterFuture()
.
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.
# NOT RUN {
## Use cluster futures
cl <- parallel::makeCluster(2L, 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)
v <- value(f)
print(v)
stopifnot(v == 0)
## CLEANUP
parallel::stopCluster(cl)
# }
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