[R] MC_CORES and mc.cores for parallel package

[Charles C. Berry]

On Wed, 7 Dec 2016, Marc Girondot via R-help wrote:

> Hi,
>
> From the documentation of ?options
>
> Options set in package parallel
> These will be set when package parallel (or its namespace) is loaded if not 
> already set.
>
> mc.cores:
> a integer giving the maximum allowed number of additional R processes allowed 
> to be run in parallel to the current R process. Defaults to the setting of 
> the environment variable MC_CORES if set. Most applications which use this 
> assume a limit of 2 if it is unset.
>

As advertised.

- Start R with no MC_CORES specified:
- check environment var
- set environment var
- check options
- THEN load parallel
- check option again

  Sys.getenv("MC_CORES")
[1] ""
> Sys.setenv("MC_CORES"=3L)
> options("mc.cores")
$mc.cores
NULL

> library(parallel)
> options("mc.cores")
$mc.cores
[1] 3

---

I think you confused things by loading parallel *before* setting the 
environment var.

HTH,

Chuck