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

[Tomas Kalibera]

Thanks, fixed in R-devel and R-patched.

The error happens in the child process when it is already exiting, after 
it had delivered a result, so this should not cause any trouble in an 
unpatched version of R (apart from showing that message). It is specific 
to mccollect(wait=FALSE).

Best
Tomas

On 5/3/19 12:47 PM, Pavel Krivitsky wrote:
> 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
>
>
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