Enhancement request: anonymous connections

On 12/28/2005 9:50 AM, Seth Falcon wrote:

On 27 Dec 2005, murdoch at stats.uwo.ca wrote:

This is a bug in load, isn't it?  load() opens the connection but
doesn't close it.

Well, it may be that load needs a small fix, but that doesn't fix
anonymous connections in general, IMO.

No it doesn't.  However, I've committed the small fix.

The loop could easily have been:

for (i in 1:50) {
    print(load(url(testUrl, open="r")))
}

And it doesn't need to be related to url or load:

cat("a line of text\n", file="another-example.txt")
z <- NULL
for (i in 1:50) {
    z <- c(z, readLines(file("another-example.txt", open="r")))
}

Also, connections are "in use" even if they are closed:

for (i in 1:50) {
    if (isOpen(file("another-example.txt")))
        stop("you will not get here")
}

I think the general problem is that R doesn't have references (or at
least, they aren't in a final, documented state).  If the garbage
collector closed a connection, then things would go wrong when there
were two copies of it:  the second one would be messed up when the first
was destroyed.  If we had references, then opening a connection could
create a connection object and a reference to it; the connection object
would remain as long as there were any references to it, and could be
destroyed (and automatically closed) after the last reference was gone.

On Sun, 1 Jan 2006, Duncan Murdoch wrote:

On 12/28/2005 9:50 AM, Seth Falcon wrote:

On 27 Dec 2005, murdoch at stats.uwo.ca wrote:

This is a bug in load, isn't it?  load() opens the connection but
doesn't close it.

Well, it may be that load needs a small fix, but that doesn't fix
anonymous connections in general, IMO.

No it doesn't.  However, I've committed the small fix.

It was not even a bug in load: close() and open() are not pairs.  (I 
didn't pick the names!) Your `fix' destroys a connection, which is 
not the documented behaviour and far more dangerous than leaving it open.

The lifecycle of a connection is  (see e.g. my R-news article)

 	create->open->close->destroy

and close() does both of the last two.  Please revert this change. 
Ideally we would close and not destroy if the connection was opened, but 
that needs a better C-level interface in place of this R-level one.

The loop could easily have been:

for (i in 1:50) {
   print(load(url(testUrl, open="r")))
}

And it doesn't need to be related to url or load:

cat("a line of text\n", file="another-example.txt")
z <- NULL
for (i in 1:50) {
   z <- c(z, readLines(file("another-example.txt", open="r")))
}

Also, connections are "in use" even if they are closed:

for (i in 1:50) {
   if (isOpen(file("another-example.txt")))
       stop("you will not get here")
}

I think the general problem is that R doesn't have references (or at
least, they aren't in a final, documented state).  If the garbage
collector closed a connection, then things would go wrong when there
were two copies of it:  the second one would be messed up when the first
was destroyed.  If we had references, then opening a connection could
create a connection object and a reference to it; the connection object
would remain as long as there were any references to it, and could be
destroyed (and automatically closed) after the last reference was gone.

However, that just isn't how connections are documented in the Green Book 
(referenced on all the relevant help pages, so required reading) and 
getConnection() allows you to create an R object pointing to a connection 
that previously had none.  The OP has never told us what `anonymous 
connections' are, but it is quite possible that his unstated ideas are 
incompatible with the documentation.

However, that just isn't how connections are documented in the Green
Book (referenced on all the relevant help pages, so required
reading) and getConnection() allows you to create an R object
pointing to a connection that previously had none.  

The OP has never told us what anonymous connections' are, but it is
quite possible that his unstated ideas are incompatible with the
documentation.