[R-sig-hpc] Warning "closing unused connection..." with package parallel

[Dirk Eddelbuettel]

On 22 January 2012 at 15:33, Zepu Zhang wrote:
| Dear list,
| 
| After running the following chunk of code repeatedly in a package
| 
| library(parellel)
| 
| f <- function(nsim, ...)
| {
|         cl <- makeCluster(detectCores())
|         on.exit(stopCluster(cl))
|         rng.kind <- RNGkind()
|         on.exit(RNGkind(rng.kind[1], rng.kind[2]))
|         RNGkind("L'Ecuyer-CMRG")
|         clusterSetRNGStream(cl, trunc(runif(1) * 10000))
| 
|         z <- clusterApply(cl, seq_len(nsim),
|                 function(dummy, ...)
|                    { #some custom function that does simulation
|                    },
|                 # additional arguments passed into function
|                 )
|       # other stuff
| }
| 
| I got > 50 warnings like
| 
| 34: closing unused connection 3 (<-localhost.localdomain:10187)
| 35: closing unused connection 4 (<-localhost.localdomain:10187)
| 36: closing unused connection 3 (<-localhost.localdomain:10187)
| 37: closing unused connection 4 (<-localhost.localdomain:10187)
| 38: closing unused connection 3 (<-localhost.localdomain:10187)
| 
| I've tested this on two Linux boxes with detectCores() returning 2 and
| 4, respectively, getting the same type of warnings. Although 2 and 4
| cores seem to be few, I need this parallel capabilities so that it's
| beneficial when the code is run on machines with more cores. It will
| be run on both Linux and Windows.
| 
| The function called by 'clusterApply' calls package 'RandomFields' for
| simulations. It is not apparent that 'RandomFields' does parallel
| computations (which might interfere with R).
| 
| Any idea what caused these warning messages? If they are harmless, I
| really want to avoid them b/c they can mask other useful warnings.

Try calling stopCluster(cl) when you're done. The documentation, accessible
via help(makeCluster,package="parallel") states this:

     It is good practice to shut down the workers by calling
     ‘stopCluster’: however the workers will terminate themselves once
     the socket on which they are listening for commands becomes
     unavailable, which it should if the master R session is completed
     (or its process dies).

Dirk

| 
| Thanks!
| 
| Zepu Zhang
| 
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