[R] PSOCK cluster and renice

[Henrik Bengtsson]

Looks like a bug to me due to wrong assumptions about 'nice'
arguments, but could be because a "non-standard" 'nice' is used.  If
we do:

> trace(system, tracer = quote(print(command)))
Tracing function "system" in package "base"

we see that the system call used is:

> cl <- parallel::makePSOCKcluster(2L, renice = 19)
Tracing system(cmd, wait = FALSE) on entry
[1] "nice +19 '/usr/lib/R/bin/Rscript'
--default-packages=datasets,utils,grDevices,graphics,stats,methods -e
'parallel:::.slaveRSOCK()' MASTER=localhost PORT=11146 OUT=/dev/null
TIMEOUT=2592000 XDR=TRUE"
nice: ‘+19’: No such file or directory
^C

The code that prepends that 'nice +19' is in parallel:::newPSOCKnode:

    if (!is.na(renice) && renice)
        cmd <- sprintf("nice +%d %s", as.integer(renice), cmd)

I don't know where that originates from and on what platform it was
tests/validated.  On Ubuntu 16.04, CentOS 6.6, and CentOS 7.4, I have
'nice' from "GNU coreutils" and they all complain about using '+',
e.g.

$ nice +19 date
nice: +19: No such file or directory

but '-' works:

$ nice -19 date
Sun Dec  3 20:01:31 PST 2017

Neither 'nice --help' nor 'man help' mention the use of a +n option.


WORKAROUND:  As a workaround, you can use:

cl <- future::makeClusterPSOCK(2L, rscript = c("nice",
"--adjustment=10", file.path(R.home("bin"), "Rscript")))

which is backward compatible with parallel::makePSOCKcluster() but
provides you with more detailed control.  Try adding verbose = TRUE to
see what the exact call looks like.

/Henrik


On Sun, Dec 3, 2017 at 7:35 PM, Andreas Leha
<andreas.leha at med.uni-goettingen.de> wrote:
> Hi all,
>
> Is it possible to use the 'renice' option together with parallel
> clusters of type 'PSOCK'?  The help page for parallel::makeCluster is
> not specific about which options are supported on which types and I am
> getting the following message when passing renice = 19 :
>
>> cl <- parallel::makeCluster(2, renice = 19)
> nice: ‘+19’: No such file or directory
>
> Kind regards,
> Andreas
>
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