R devel - Apr 2013 - parallel::mclapply does not return try-error objects with mc.preschedule=TRUE

Hello,

Consider this:

1)
library(parallel)
res <- mclapply(1:2, stop)
#Warning message:
#In mclapply(1:2, stop) :
# all scheduled cores encountered errors in user code

is(res[[1]], 'try-error')
#[1] FALSE


2)
library(parallel)
res <- mclapply(1:2, stop, mc.preschedule=FALSE)
#Warning message:
#In mclapply(1:2, stop, mc.preschedule = FALSE) :
#  2 function calls resulted in an error

is(res[[1]], 'try-error')
#[1] TRUE

The documentation states that:
'Each forked process runs its job inside try(..., silent = TRUE) so if
errors occur they will be stored as class "try-error" objects in the
return value and a warning will be given.'


Is this a bug ?

Thanks
Karl

> sessionInfo()
R version 2.15.3 (2013-03-01)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=C                 LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] parallel  stats     graphics  grDevices utils     datasets  methods
[8] base

loaded via a namespace (and not attached):
[1] tools_2.15.3

On 11/04/2013 12:43, Karl Forner wrote:
> Hello,
>
> Consider this:
>
> 1)
> library(parallel)
> res <- mclapply(1:2, stop)
> #Warning message:
> #In mclapply(1:2, stop) :
> # all scheduled cores encountered errors in user code
>
> is(res[[1]], 'try-error')
> #[1] FALSE
>
>
> 2)
> library(parallel)
> res <- mclapply(1:2, stop, mc.preschedule=FALSE)
> #Warning message:
> #In mclapply(1:2, stop, mc.preschedule = FALSE) :
> #  2 function calls resulted in an error
>
> is(res[[1]], 'try-error')
> #[1] TRUE
>
> The documentation states that:
> 'Each forked process runs its job inside try(..., silent = TRUE) so if
> errors occur they will be stored as class "try-error" objects in
the
> return value and a warning will be given.'
>
>
> Is this a bug ?
Not in parallel.  Something else has changed, and I am about to commit a 
different version that still works as documented.
>
> Thanks
> Karl
>
>
>> sessionInfo()
> R version 2.15.3 (2013-03-01)
> Platform: x86_64-unknown-linux-gnu (64-bit)
>
> locale:
>   [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
>   [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
>   [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
>   [7] LC_PAPER=C                 LC_NAME=C
>   [9] LC_ADDRESS=C               LC_TELEPHONE=C
> [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C
>
> attached base packages:
> [1] parallel  stats     graphics  grDevices utils     datasets  methods
> [8] base
>
> loaded via a namespace (and not attached):
> [1] tools_2.15.3
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595