[R] process id of an R script

[Charles Berry]

Mikkel Grum <mi2kelgrum <at> yahoo.com> writes:

> 
> I have a script that runs as a cron job every minute (on Ubuntu 10.10 and R
2.11.1), querying a database for new
> data. Most of the time it takes a few seconds to run, but once in while it
takes more than a minute and the next
> run starts (on the same data) before the previous one has finished. In extreme
cases this will fill up
> memory with a large number of runs of the same script on the same data. My
'solution' has been to create a
> process id file with the currently running script, first checking whether
there is another process id
> file and whether that process is still running. I use the following code:
> 
> pid <- max(system("pgrep -x R", intern = TRUE))
> if (file.exists("/var/run/myscript.pid")) {
> rm(pid)
> pid <- read.table("/var/run/myscript.pid")[[1]]
> if (length(system(paste("ps -p", pid), intern = TRUE)) != 2) {
> stop("Myscript is already running in another process.")
> } else {
> pid <- max(system("pgrep -x R", intern = TRUE))
> write(pid, "/var/run/myscript.pid")
> }
> } else {
> write(pid, "/var/run/myscript.pid")
> }
> 
> ....my script .....
> 
> file.remove("/var/run/myscript.pid")
> #The End
> 
> The trouble here is that I also have other R scripts running on the same
system, so
> while max(system("pgrep -x R", intern = TRUE)) will almost always give me the
right pid, it is not
> guaranteed to work. There are two situations where it could fail: when the
process id numbers round 32000
> and start over again, and if another process starts up at the same time, the
process ids could get swapped.
> 
> Is there a way to query for the process id of the specific R script, rather
than all R processes?

Yes.

Following the posting guide, you try something like

   ?process

which will tell you to try

   ??process

which will list

base::Rdconv                        Utilities for Processing Rd Files
base::Sys.getpid                    Get the Process ID of the R Session
[rest deleted]

Sys.getpid seems to be the relevant function.


HTH, 

Chuck