Is there a way to refresh capabilities("X11") without restarting R
such that it reflects the enabling/disabling of X11?
BACKGROUND:
If I launch R with X11 server disabled (e.g. ssh -X / ssh -Y to remote
Linux but forgot to enable Xming on local Windows), then I get:
> capabilities("X11")
X11
FALSE
> x11()
Error in .External2(C_X11, d$display, d$width, d$height, d$pointsize, :
unable to start device X11cairo
In addition: Warning message:
In x11() : unable to open connection to X11 display ''
So far so good. However, if I then enable the X11 server (e.g. start
Xming on Windows), I still get:
> capabilities("X11")
X11
FALSE
but
> x11()
successfully opens an X11 plot window. In other words, the value of
capabilities("X11") is not reflecting the availability of X11; from
?capabilities:
X11: Are the 'X11' graphics device and the X11-based data editor
available? This loads the X11 module if not already loaded,
and checks that the default display can be contacted unless a
'X11' device has already been used.
Not sure what that last "...unless a 'X11' device has already been
used" actually means here; is it a disclaimer for the above behavior?
If I restart R, the I get:
> capabilities("X11")
X11
TRUE
I came up with the following approach that launches another R session
querying the availability of X11:
capabilitiesX11 <- function() {
bin <- file.path(R.home("bin"), "Rscript")
cmd <- "cat(capabilities('X11'))"
value <- system2(bin, args=c("-e", dQuote(cmd)), stdout=TRUE)
as.logical(value)
}
> capabilitiesX11()
[1] TRUE
but it's certainly feels like a hack.
Is there a way to force a refresh of capabilities("X11") without restarting R?
BTW, the description of ?capabilities says: "Report on the optional
features which have been compiled into this build of R." The
"compiled into this build" part seems too specific; the above shows
that capabilities() also reflects run-time availabilities. Other
"properties" does this as well.
Thanks,
Henrik
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