[R-sig-hpc] multicore:pvec error when length of v is less than number of cores

[Cook, Malcolm]

Hi Simon et al,

I find that the return value of multicore:pvec includes error messages when the length of input vector is less than number of cores.

Additionally, to accomodate the error message being a character, any other non message results wind up being coerced to strings.

Here is an example running on my 16 core computer:

> tail(pvec(1:(multicore:::detectCores()-1),identity))
[1] "11"                                         
[2] "12"                                         
[3] "13"                                         
[4] "14"                                         
[5] "15"                                         
[6] "Error in l[[i]] : subscript out of bounds\n"
Warning message:
In pvec(1:(multicore:::detectCores() - 1), identity) :
  some results may be missing, folded or caused an error

The logic of computing the array indices needs revisiting.
I quick-patched it by setting:
  cores <- min(cores,n)
right after pvec sets
  n <- length(v)

and now I get:

> tail(pvec(1:(multicore:::detectCores()-1),identity))
[1] 10 11 12 13 14 15

Better?

-Malcolm