[Rd] Strange error messages from parallel::mcparallel family under 3.6.0

[Pavel Krivitsky]

Dear All,

Since upgrading to 3.6.0, I've been getting a strange error messages
from the child process when using mcparallel/mccollect. Before filing a report in the Bugzilla, I want to figure out whether I had been doing something wrong all this time and R 3.6.0 has exposed it, or whether something else is going on.

# Background #

Ultimately, what I want to do is to be able to set a time limit for an
expression to be evaluated that would be enforced even inside compiled
code. (R.utils::withTimeout() uses base::setTimeLimit(), which can only
enforce within R code.)

# Implementation #

The approach that my implementation, statnet.common::forkTimeout()
(source attached for convenience), uses is to call mcparallel() to
evaluate the expression in a child process, then mccollect() with
wait=FALSE and a timeout to give it a chance to finish. If it runs past
the timeout, the child process is killed and an onTimeout value is
returned. (This only works on Unix-alikes, but it's better than
nothing.)

# The problem #

Since 3.6.0---and I've tested fresh installs of 3.6.0 and 3.5.3 side-
by-side---I've been getting strange messages.

Running

  source("forkTimeout.R") # attached
  repeat print(forkTimeout({Sys.sleep(1);TRUE}, timeout=3))

results in

[1] TRUE
[1] TRUE
Error in mcexit(0L) : ignoring SIGPIPE signal
[1] TRUE
[1] TRUE
Error in mcexit(0L) : ignoring SIGPIPE signal
[1] TRUE
[1] TRUE
[1] TRUE

until interrupted. Running

  options(error=traceback)
  repeat print(forkTimeout({Sys.sleep(1);TRUE}, timeout=3))

results in sporadic messages of the form:

Error in mcexit(0L) : ignoring SIGPIPE signal
6: selectChildren(jobs, timeout)
5: parallel::mccollect(child, wait = FALSE, timeout = timeout) at
forkTimeout.R#75
4: withCallingHandlers(expr, warning = function(w)
invokeRestart("muffleWarning"))
3: suppressWarnings(parallel::mccollect(child, wait = FALSE, timeout =
timeout)) at forkTimeout.R#75
2: forkTimeout({
       Sys.sleep(1)
    ...
1: print(forkTimeout({
       Sys.sleep(1)
    ...

So, these messages do not appear to prevent the child process from
returning valid output, but I've never seen them before R 3.6.0, so I
wonder if I am doing something wrong. Session info is also attached.

				Thanks in advance,
				Pavel

-- 
Pavel Krivitsky
Lecturer in Statistics
National Institute of Applied Statistics Research Australia (NIASRA)
School of Mathematics and Applied Statistics | Building 39C Room 154
University of Wollongong NSW 2522 Australia
T +61 2 4221 3713
Web (NIASRA): http://niasra.uow.edu.au/index.html
Web (Personal): http://www.krivitsky.net/research
ORCID: 0000-0002-9101-3362

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