mirai (version 2.2.0)

everywhere: Evaluate Everywhere

Description

Evaluate an expression 'everywhere' on all connected daemons for the specified compute profile - this must be set prior to calling this function. Designed for performing setup operations across daemons by loading packages or exporting common data. Resultant changes to the global environment, loaded packages and options are persisted regardless of a daemon's cleanup setting.

Usage

everywhere(.expr, ..., .args = list(), .compute = "default")

Value

A list of mirai executed on each daemon. This may be waited for and inspected using call_mirai() or collect_mirai().

Arguments

.expr

an expression to evaluate asynchronously (of arbitrary length, wrapped in { } where necessary), or else a pre-constructed language object.

...

(optional) either named arguments (name = value pairs) specifying objects referenced, but not defined, in .expr, or an environment containing such objects. See 'evaluation' section below.

.args

(optional) either a named list specifying objects referenced, but not defined, in .expr, or an environment containing such objects. These objects will remain local to the evaluation environment as opposed to those supplied in ... above - see 'evaluation' section below.

.compute

[default 'default'] character value for the compute profile to use (each compute profile has its own independent set of daemons).

Evaluation

The expression .expr will be evaluated in a separate R process in a clean environment (not the global environment), consisting only of the objects supplied to .args, with the objects passed as ... assigned to the global environment of that process.

As evaluation occurs in a clean environment, all undefined objects must be supplied through ... and/or .args, including self-defined functions. Functions from a package should use namespaced calls such as mirai::mirai(), or else the package should be loaded beforehand as part of .expr.

For evaluation to occur as if in your global environment, supply objects to ... rather than .args, e.g. for free variables or helper functions defined in function bodies, as scoping rules may otherwise prevent them from being found.

Details

This function should be called when no other mirai operations are in progress. If necessary, wait for all mirai operations to complete. This is as this function does not force a synchronization point, and using concurrently with other mirai operations does not guarantee the timing of when the instructions will be received, or that they will be received on each daemon.

Examples

if (FALSE) { # interactive()
daemons(1)
# export common data by a super-assignment expression:
everywhere(y <<- 3)
# '...' variables are assigned to the global environment
# '.expr' may be specified as an empty {} in such cases:
everywhere({}, a = 1, b = 2)
m <- mirai(a + b - y == 0L)
m[]
# everywhere() returns a list of mirai which may be waited for and inspected
mlist <- everywhere("just a normal operation")
collect_mirai(mlist)
mlist <- everywhere(stop("error"))
collect_mirai(mlist)
daemons(0)

# loading a package on all daemons
daemons(1, dispatcher = FALSE)
everywhere(library(parallel))
m <- mirai("package:parallel" %in% search())
m[]
daemons(0)
}