R devel - Mar 2003 - RE: [R] File opening error after 1020 files opened

Maybe open.connection() should also check if the connection is already
open and given an error or at least a warning if it is. Suggested code
update:

open.connection <- function(con, open="r", blocking=TRUE, ...) {
  if (!inherits(con, "connection"))
    stop("argument is not a connection")
  if (isOpen(con))                                               # NEW
    stop("Trying to open a connection that is already open.")    # NEW
  invisible(.Internal(open(con, open, blocking)))
}

Henrik Bengtsson

> -----Original Message-----
> From: Roger Bivand [mailto:Roger.Bivand@nhh.no] 
> Sent: den 1 mars 2003 06:25
> To: ripley@stats.ox.ac.uk
> Cc: Dirk Eddelbuettel; jonathan_li@agilent.com; hb@maths.lth.se
> Subject: Re: [R] File opening error after 1020 files opened
> 
> 
> On Fri, 28 Feb 2003 ripley@stats.ox.ac.uk wrote:
> 
> > Let's take this off R-help.
> > 
> > I did a quick check that connections are behaving:
> > 
> > for(i in 1:2000) {
> > print(i)
> > zz <- file("foo", "rb")
> > foo <- readLines(zz)
> > close(zz)
> > }
> > 
> > for(i in 1:2000) {
> > print(i)
> > zz <- file(tempfile(), "wb")
> > cat("foobar\n", file=zz)
> > close(zz)
> > }
> > 
> > work for me, several times in a session in both Windows and 
> Linux. I 
> > do know that sometimes under Windows file closing fails, but not 
> > often.
> > 
> > The file-handle limit on RH7.2 seems to 8096, and I used at least 
> > 20000 opens.
> > 
> > However, read.pnm has
> > 
> >     con <- file(file, open = "rb")
> >     open(con, open = "rb")
> > ...
> >     close(con)
> 
> Yes, of course. Revision (pixmap_0.3-2.tar.gz) on incoming, 
> should be on 
> CRAN before long. If needed, I can attach it. Runs 10000 
> read.pnm() now 
> without difficulty. I can't recall why I once thought file() 
> just set a 
> handle and open() actually opened it, wrong assumptions can 
> survive for 
> years!
> 
> Thanks,
> 
> Roger
> 
> > 
> > which opens the connection *twice* and that's creating two file 
> > handles and only closing one.  See ?file.
> > 
> > Brian
[SNIP]

It already does, at a lower level where it will always
check.
>From the NEWS file:
    o   An attempt to open() an already open connection will be detected
	and ignored with a warning.  This avoids improperly closing
	some types of connections if they are opened repeatedly.

Please check such things first ....


On Sat, 1 Mar 2003, Henrik Bengtsson wrote:
> Maybe open.connection() should also check if the connection is already
> open and given an error or at least a warning if it is. Suggested code
> update:
> 
> open.connection <- function(con, open="r", blocking=TRUE, ...)
{
>   if (!inherits(con, "connection"))
>     stop("argument is not a connection")
>   if (isOpen(con))                                               # NEW
>     stop("Trying to open a connection that is already open.")   
# NEW
>   invisible(.Internal(open(con, open, blocking)))
> }
> 
> Henrik Bengtsson
> 
> 
> > -----Original Message-----
> > From: Roger Bivand [mailto:Roger.Bivand@nhh.no] 
> > Sent: den 1 mars 2003 06:25
> > To: ripley@stats.ox.ac.uk
> > Cc: Dirk Eddelbuettel; jonathan_li@agilent.com; hb@maths.lth.se
> > Subject: Re: [R] File opening error after 1020 files opened
> > 
> > 
> > On Fri, 28 Feb 2003 ripley@stats.ox.ac.uk wrote:
> > 
> > > Let's take this off R-help.
> > > 
> > > I did a quick check that connections are behaving:
> > > 
> > > for(i in 1:2000) {
> > > print(i)
> > > zz <- file("foo", "rb")
> > > foo <- readLines(zz)
> > > close(zz)
> > > }
> > > 
> > > for(i in 1:2000) {
> > > print(i)
> > > zz <- file(tempfile(), "wb")
> > > cat("foobar\n", file=zz)
> > > close(zz)
> > > }
> > > 
> > > work for me, several times in a session in both Windows and 
> > Linux. I 
> > > do know that sometimes under Windows file closing fails, but not 
> > > often.
> > > 
> > > The file-handle limit on RH7.2 seems to 8096, and I used at least
> > > 20000 opens.
> > > 
> > > However, read.pnm has
> > > 
> > >     con <- file(file, open = "rb")
> > >     open(con, open = "rb")
> > > ...
> > >     close(con)
> > 
> > Yes, of course. Revision (pixmap_0.3-2.tar.gz) on incoming, 
> > should be on 
> > CRAN before long. If needed, I can attach it. Runs 10000 
> > read.pnm() now 
> > without difficulty. I can't recall why I once thought file() 
> > just set a 
> > handle and open() actually opened it, wrong assumptions can 
> > survive for 
> > years!
> > 
> > Thanks,
> > 
> > Roger
> > 
> > > 
> > > which opens the connection *twice* and that's creating two
file
> > > handles and only closing one.  See ?file.
> > > 
> > > Brian
> 
> [SNIP]
> 
> 
-- 
Brian D. Ripley,                  ripley@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 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595