connections: remember to close it!
On Tue, 2 Oct 2001, Liaw, Andy wrote:
Hi all, I have newly discovered the power of connections (although just a small part of it, namely the file() connection). It allowed me to process data file with arbitrary number of fields per line, which I was using awk for preprocessing before readling into R. The combination of the connection, readLines() and strsplit() really make the work a lot easier and more organized. Thanks a bundle to the R Core for this excellent work!! One reminder for people new to connections: If you open connections inside a function, make sure they are closed before exiting from that function, otherwise you end up with connections that can not be closed (or at least I tried closeAllConnections() without success on WinNT4). Not being very smart or clear-headed, I turned a working R script that opens the connection and process the data into an R function, but introduced some bugs in the process. I forgot to add "on.exit(close(filecon))" right after I open the connection in the function. As a result, repeated failed calls to the function generated a bunch of open connections that I can't close. I'm not sure what the consequences of this is. I was able to quit R gracefully, but my NT seemed to have become unstable afterward.
Some terminology:
`close' closes and destroys a connection.
`closeAllConnections' closes all open user connections.
Notice the distinction.
You can close and destroy connections later. Just call
showConnections(all=FALSE) and then use
close(getConnection(some.number)). This *is* on the *same* help page as
closeAllConnections.
closeAllConnections was broken when close was made generic. It should read
function ()
{
set <- getAllConnections()
set <- set[set > 2]
for (i in seq(along = set)) close(getConnection(set[i]))
invisible()
}
and needs to be amended to handle the sink stack.
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272860 (secr) Oxford OX1 3TG, UK Fax: +44 1865 272595 -.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.- r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html Send "info", "help", or "[un]subscribe" (in the "body", not the subject !) To: r-help-request at stat.math.ethz.ch _._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._