snow, stopping cluster

Hello,

is there any function in the package snow to check for a really running 
cluster?
The function checkCluster only checks the variable cl. And the variable 
is still available after stopping the cluster!
( a simple solution would be deleting the cluster variable cl in the 
function stopCluster)

 > library(snow)
 > cl <- makeCluster(5)
        5 slaves are spawned successfully. 0 failed.
 > clusterApply(cl, 1:2, get("+"), 3)
[[1]]
[1] 4

[[2]]
[1] 5

 > stopCluster(c1)
[1] 1
 > clusterApply(cl, 1:2, get("+"), 3)
Fehler in mpi.probe(source, tag, comm, status) :
  MPI_Error_string: invalid communicator


 > sessionInfo()
R version 2.6.0 (2007-10-03)
x86_64-unknown-linux-gnu

locale:
LC_CTYPE=de_DE.UTF-8;LC_NUMERIC=C;LC_TIME=de_DE.UTF-8;LC_COLLATE=de_DE.UTF-8;LC_MONETARY=de_DE.UTF-8;LC_MESSAGES=de_DE.UTF-8;LC_PAPER=de_DE.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=de_DE.UTF-8;LC_IDENTIFICATION=C

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

other attached packages:
[1] affyPara_0.99.2      affy_1.16.0          preprocessCore_1.0.0
[4] affyio_1.6.1         Biobase_1.16.1       Rmpi_0.5-5         
[7] snow_0.2-9         

loaded via a namespace (and not attached):
[1] rcompgen_0.1-15


Best
Markus

Dipl.-Tech. Math. Markus Schmidberger

Ludwig-Maximilians-Universit?t M?nchen
IBE - Institut f?r medizinische Informationsverarbeitung,
Biometrie und Epidemiologie
Marchioninistr. 15, D-81377 Muenchen
URL: http://ibe.web.med.uni-muenchen.de 
Mail: Markus.Schmidberger [at] ibe.med.uni-muenchen.de
Tel: +49 (089) 7095 - 4599