[Rd] Possible changes to connections

[Bill Dunlap]

On Thu, 31 May 2007, Seth Falcon wrote:

> > When I ran some tests I found 7 packages on CRAN that in their tests
> > were not closing connections.  Four of those are maintained by R-core
> > members.
> > Even though none were by me, I think this is too easy to forget to
> > do!
>
> I agree that it is easy to forget.  It is especially easy if one
> creates so-called anonymous connection references like
> readLines(file(path)) -- this anonymous idiom seems nature to me when
> coding R and it would be nice to make it work for connections.

I like the idea of the connection being closed when there
are no more references to it.  I guess that means when the
garbage collector notices it has been orphaned, which may
take a while.

However, one of my longstanding complaints about connections
in Splus and R may have a bearing here also.  Currently, if you
want to have your file opened in a particular way, say for
only reading or for appending or in binary mode then you
need to specify open=mode when calling file().  However that
also tells it to actually open the file.  I would prefer that
there was a mode= argument to file that meant that when the
file is eventually opened it would be opened with that mode.
open= should be restricted to TRUE or FALSE, or IMO, be eliminated.
(We have an open() function for that.)  With the current system
   readLines(file(path))
does not leave path open but
   readLines(file(path, "r"))
does leave it open.  E.g., using readLines(file(path))
as Seth did appears to work fine:
  > system(paste("/usr/sbin/lsof -p", Sys.getpid(),"|grep /tmp/twolines.txt"))
  > readLines(file("/tmp/twolines.txt"))
  [1] "One,"                 "two, and that is it."
  > system(paste("/usr/sbin/lsof -p", Sys.getpid(),"|grep /tmp/twolines.txt"))
  > # no lsof output means the file is not open
but asking to have it opened in readonly and binary
mode leaks a file descriptor:
  > system(paste("/usr/sbin/lsof -p", Sys.getpid(),"|grep /tmp/twolines.txt"))
  > readLines(file("/tmp/twolines.txt", open="rb"))
  [1] "One,"                 "two, and that is it."
  > system(paste("/usr/sbin/lsof -p", Sys.getpid(),"|grep /tmp/twolines.txt"))
  R       16950 bill    3r   REG    8,2       26   229597 /tmp/twolines.txt
That difference sinces unnatural to me.

Of course, we could just add the mode= argument and hope
people started using it instead of open=.

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Bill Dunlap
Insightful Corporation
bill at insightful dot com
360-428-8146

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