Evaluate an expression 'everywhere' on all connected daemons for the
specified compute profile - this must be set prior to calling this function.
Performs operations across daemons such as 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 = NULL)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 NULL] character value for the compute profile to use (each has its own independent set of daemons), or NULL to use the 'default' profile.
Details
If using dispatcher, this function forces a synchronization point at
dispatcher, whereby the everywhere() call must have been evaluated on all
daemons prior to subsequent evaluations taking place.
It is an error to call everywhere() successively without at least one
mirai() call in between, as an ordinary mirai call is required to exit each
synchronization point.
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 non-local variables or helper functions
required by other functions, as scoping rules may otherwise prevent them from
being found.
Examples
if (FALSE) { # interactive()
daemons(1)
# export common data by a super-assignment expression:
everywhere(y <<- 3)
mirai(y)[]
# '...' variables are assigned to the global environment
# '.expr' may be specified as an empty {} in such cases:
everywhere({}, a = 1, b = 2)
mirai(a + b - y == 0L)[]
# everywhere() returns a mirai_map object:
mp <- everywhere("just a normal operation")
mp
mp[]
daemons(0)
# loading a package on all daemons
daemons(1, dispatcher = FALSE)
everywhere(library(parallel))
m <- mirai("package:parallel" %in% search())
m[]
daemons(0)
}