[R] print and cat not working with parallelised functions?

[Uwe Ligges]

On 08.12.2012 21:04, Martin Ivanov wrote:
>   Dear R Community,
>
> I am running R version 2.15.2 with package parallel version 2.15.2.
> The problem is that cat and print do not produce any output. Also assigning objects to the .GlobalEnv does not work. This makes it difficult for me to debug code. This can be seen from the
> following minimal working example:
>


print: You are printing in the R client, not on the master
assign: You are assigning to the .GlobalEnv of the client, not the one 
of the master.

Best,
Uwe Ligges



> library(parallel)
> fun2 <- function(x) {
> b <<- x; # try to export the object to the workspace
> print(x); # try to print x
> }
>
> fun1 <- function(d) {
>   cl <- makeCluster(getOption("cl.cores", detectCores()));
>   parSapply(cl=cl, X=seq_along(d), FUN=fun2);
>   stopCluster(cl=cl);
> }
> fun3 <- function(d) sapply(X=seq_along(d), FUN=fun2);
> fun1(d=1:5)
> a <- fun3(d=1:5)
>
> print only works when fun3 is called, that is when there is no parallelisation. The
> same is also true for the <<- assignment.
> I am almost sure this is not a bug, but a feature, so I would like to ask you
> for some explanation and also for some ideas how to handle debugging code when
> no printing or exporting objects to the workspace works.
>
> Any suggestions will be appreciated.
>
> Best regards,
>
> Martin Ivanov
>
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