$ tail Rtest1.txt 

0.05
0.05
0.05
0.05
0.05
0.05
0.13
0.08
0.10
0.15

$ wc -l Rtest1.txt 

91135 Rtest1.txt

$ cp Rtest1.txt Rtest2.txt 

$ cat Rtest1.R

library(splines)
library(survival)
library(NADA)
outcome=scan("Rtest1.txt")
cenoutcome=rep(FALSE, length(outcome))
cenoutcome[outcome==min(outcome)]=TRUE
pyros=cenros(outcome,cenoutcome)
mean(pyros)
proc.time()

# Rtest2.R is the same, but it reads Rtest2.txt

$ Rscript Rtest1.R 2> /dev/null &

[1] 0.03195313
   user  system elapsed 
 22.201   4.096  26.293 


$ Rscript Rtest1.R 2> /dev/null & Rscript Rtest2.R 2> dev/null &

[1] 0.03195313
   user  system elapsed 
 40.358   6.328  46.839 
[1] 0.03195313
   user  system elapsed 
 39.706   6.044  48.128