Re: [Rd] isOpen on closed connections
My solution the original post is to always set 'con - NULL' after closing a
connection, and then test for NULL. This is how I do to make sure to make
sure that opened connections are closed and as soon as possible.
foo - function(...) {
con - file(foo.R, open=r):
on.exit({
if (!is.null(con)) {
close(con);
con - NULL;
}
})
# Do some thing that might cause foo() to exit.
bar();
# Do some thing else
cat(con, foo);
# Close connection as soon as possible
close(con);
con - NULL;
# Do more things before returning
}
However, is there a reason for not having isOpen() return FALSE after
close() with the logic that a destroy connection is also a non-open one?
So, basically:
isOpen - function (con, rw = ) {
rw - pmatch(rw, c(read, write), 0)
res - FALSE
tryCatch({
res - .Internal(isOpen(con, rw))
}, error = function(ex) {
})
res
}
EXAMPLE:
con - file(foo.R)
print(isOpen(con))
[1] FALSE
open(con, w)
print(isOpen(con))
[1] TRUE
close(con)
print(isOpen(con))
[1] FALSE
open(con, w)
Error in open.connection(con, w) : invalid connection
If there is a use case that needs to test if a connection has been
destroyed, it would be more natural to add isDestroyed(), although I cannot
really see where it should be needed.
/Henrik
On Nov 14, 2007 11:18 PM, Prof Brian Ripley [EMAIL PROTECTED] wrote:
I think the confusion here is over close(): that closes *and destroys* a
connection, so it no longer exists.
isOpen applies to existing connections: you cannot close but not destroy
them at R level, but C code can (and does). You will see it in use in the
utils package.
On Nov 14, 2007 11:18 PM, Prof Brian Ripley [EMAIL PROTECTED] wrote:
I think the confusion here is over close(): that closes *and destroys* a
connection, so it no longer exists.
isOpen applies to existing connections: you cannot close but not destroy
them at R level, but C code can (and does). You will see it in use in the
utils package.
On Wed, 14 Nov 2007, Seth Falcon wrote:
Roger D. Peng [EMAIL PROTECTED] writes:
As far as I can tell, 'isOpen' cannot return FALSE in the case when 'rw
= '.
If the connection has already been closed by 'close' or some other
function,
then isOpen will produce an error. The problem is that when isOpen
calls
'getConnection', the connection cannot be found and 'getConnection'
produces an
error. The check to see if it is open is never actually done.
I see this too with R-devel (r43376) {from Nov 6th}.
con = file(example1, w)
isOpen(con)
[1] TRUE
showConnections()
description class mode text isopen can read can write
3 example1 file w text opened no yes
close(con)
isOpen(con)
Error in isOpen(con) : invalid connection
## printing also fails
con
Error in summary.connection(x) : invalid connection
This came up in some code where I'm trying to clean up connections
after
successfully opening them. The problem is that if I try to close a
connection
that has already been closed, I get an error (because 'getConnection'
cannot
find it). But then there's no way for me to find out if a connection
has
already been closed. Perhaps there's another approach I should be
taking? The
context is basically,
con - file(foo, w)
tryCatch({
## Do stuff that might fail
writeLines(stuff, con)
close(con)
file.copy(foo, bar)
}, finally = {
close(con)
})
This doesn't address isOpen, but why do you have the call to close
inside the tryCatch block? Isn't the idea that finally will always be
run and so you can be reasonably sure that close gets called once?
If your real world code is more complicated, perhaps you can make use
of a work around like:
myIsOpen = function(con) tryCatch(isOpen(con), error=function(e) FALSE)
You could do similar with myClose and close a connection as many
times as you'd like :-)
+ seth
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics,
http://www.stats.ox.ac.uk/~ripley/http://www.stats.ox.ac.uk/%7Eripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UKFax: +44 1865 272595
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Re: [Rd] isOpen on closed connections
Upon further consideration, I realized there is a philosophical element
here---if a connection is closed and hence does not exist, is it open?
The practical issue for me is that when you do something like
close(con)
the 'con' object is still lying around and is essentially undefined. For
example, if I do
close(con)
con - hello
then it seems logical to me that 'isOpen' would return an error. But it feels
natural to me that a sequence like
close(con)
isOpen(con) ## FALSE?
would not lead to an error. Perhaps my expectations are not reasonable and I'd
appreciate being corrected.
Given Brian's comment, one solution would be to allowing closing but not
destroying connections at the R level (maybe via an option?), but that is a
change in semantics and I'm not sure if this problem really comes up that much.
-roger
Prof Brian Ripley wrote:
I think the confusion here is over close(): that closes *and destroys* a
connection, so it no longer exists.
isOpen applies to existing connections: you cannot close but not destroy
them at R level, but C code can (and does). You will see it in use in
the utils package.
On Wed, 14 Nov 2007, Seth Falcon wrote:
Roger D. Peng [EMAIL PROTECTED] writes:
As far as I can tell, 'isOpen' cannot return FALSE in the case when
'rw = '.
If the connection has already been closed by 'close' or some other
function,
then isOpen will produce an error. The problem is that when isOpen
calls
'getConnection', the connection cannot be found and 'getConnection'
produces an
error. The check to see if it is open is never actually done.
I see this too with R-devel (r43376) {from Nov 6th}.
con = file(example1, w)
isOpen(con)
[1] TRUE
showConnections()
description class mode text isopen can read can write
3 example1 file w text opened no yes
close(con)
isOpen(con)
Error in isOpen(con) : invalid connection
## printing also fails
con
Error in summary.connection(x) : invalid connection
This came up in some code where I'm trying to clean up connections after
successfully opening them. The problem is that if I try to close a
connection
that has already been closed, I get an error (because 'getConnection'
cannot
find it). But then there's no way for me to find out if a connection
has
already been closed. Perhaps there's another approach I should be
taking? The
context is basically,
con - file(foo, w)
tryCatch({
## Do stuff that might fail
writeLines(stuff, con)
close(con)
file.copy(foo, bar)
}, finally = {
close(con)
})
This doesn't address isOpen, but why do you have the call to close
inside the tryCatch block? Isn't the idea that finally will always be
run and so you can be reasonably sure that close gets called once?
If your real world code is more complicated, perhaps you can make use
of a work around like:
myIsOpen = function(con) tryCatch(isOpen(con), error=function(e) FALSE)
You could do similar with myClose and close a connection as many
times as you'd like :-)
+ seth
--
Roger D. Peng | http://www.biostat.jhsph.edu/~rpeng/
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Re: [Rd] isOpen on closed connections
I'd support a change, to having a closed-but-not-invalid status for a
'rw' connection, and to have a usable 'isOpen'. The suggestion of
relying on user-code to always housekeep after calling 'close', eg by
setting to NULL, seems a bit risky as a guideline for R as a whole (one
can never tell what convention a different author's code might follow).
And the 'myOpen' solution will work (I'm about to use it myself) but
cumbersome if everyone has to do it. With things as they are, I can
foresee a stream of why does.../RTFM emails...
Perhaps the more fundamental issue is whether 'getConnection' should
actually throw an error.
I'm getting bitten by this in R 2.6.1-- I use 'getConnection' in an
'on.exit' statement (where I can't be sure of the state of the
connection), and it's throwing an error instead of returning NULL as it
used to (and as the documentation still states).
--
Mark Bravington
CSIRO Mathematical Information Sciences
Marine Laboratory
Castray Esplanade
Hobart 7001
TAS
ph (+61) 3 6232 5118
fax (+61) 3 6232 5012
mob (+61) 438 315 623
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Roger D. Peng
Sent: Thursday, 15 November 2007 11:48 PM
To: Prof Brian Ripley
Cc: R-devel mailing list
Subject: Re: [Rd] isOpen on closed connections
Upon further consideration, I realized there is a
philosophical element here---if a connection is closed and
hence does not exist, is it open?
The practical issue for me is that when you do something like
close(con)
the 'con' object is still lying around and is essentially
undefined. For example, if I do
close(con)
con - hello
then it seems logical to me that 'isOpen' would return an
error. But it feels natural to me that a sequence like
close(con)
isOpen(con) ## FALSE?
would not lead to an error. Perhaps my expectations are not
reasonable and I'd appreciate being corrected.
Given Brian's comment, one solution would be to allowing
closing but not destroying connections at the R level (maybe
via an option?), but that is a change in semantics and I'm
not sure if this problem really comes up that much.
-roger
Prof Brian Ripley wrote:
I think the confusion here is over close(): that closes
*and destroys*
a connection, so it no longer exists.
isOpen applies to existing connections: you cannot close but not
destroy them at R level, but C code can (and does). You
will see it
in use in the utils package.
On Wed, 14 Nov 2007, Seth Falcon wrote:
Roger D. Peng [EMAIL PROTECTED] writes:
As far as I can tell, 'isOpen' cannot return FALSE in the
case when
'rw = '.
If the connection has already been closed by 'close' or
some other
function, then isOpen will produce an error. The problem is that
when isOpen calls 'getConnection', the connection cannot be found
and 'getConnection'
produces an
error. The check to see if it is open is never actually done.
I see this too with R-devel (r43376) {from Nov 6th}.
con = file(example1, w)
isOpen(con)
[1] TRUE
showConnections()
description class mode text isopen can read can write
3 example1 file w text opened no yes
close(con)
isOpen(con)
Error in isOpen(con) : invalid connection
## printing also fails
con
Error in summary.connection(x) : invalid connection
This came up in some code where I'm trying to clean up
connections
after successfully opening them. The problem is that if I try to
close a connection that has already been closed, I get an error
(because 'getConnection'
cannot
find it). But then there's no way for me to find out if a
connection has already been closed. Perhaps there's another
approach I should be taking? The context is basically,
con - file(foo, w)
tryCatch({
## Do stuff that might fail
writeLines(stuff, con)
close(con)
file.copy(foo, bar)
}, finally = {
close(con)
})
This doesn't address isOpen, but why do you have the call to close
inside the tryCatch block? Isn't the idea that finally
will always
be run and so you can be reasonably sure that close gets
called once?
If your real world code is more complicated, perhaps you
can make use
of a work around like:
myIsOpen = function(con) tryCatch(isOpen(con), error=function(e)
FALSE)
You could do similar with myClose and close a connection as many
times as you'd like :-)
+ seth
--
Roger D. Peng | http://www.biostat.jhsph.edu/~rpeng/
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Re: [Rd] isOpen on closed connections
Roger D. Peng [EMAIL PROTECTED] writes:
As far as I can tell, 'isOpen' cannot return FALSE in the case when 'rw =
'.
If the connection has already been closed by 'close' or some other function,
then isOpen will produce an error. The problem is that when isOpen calls
'getConnection', the connection cannot be found and 'getConnection' produces
an
error. The check to see if it is open is never actually done.
I see this too with R-devel (r43376) {from Nov 6th}.
con = file(example1, w)
isOpen(con)
[1] TRUE
showConnections()
description class mode text isopen can read can write
3 example1 file w text opened no yes
close(con)
isOpen(con)
Error in isOpen(con) : invalid connection
## printing also fails
con
Error in summary.connection(x) : invalid connection
This came up in some code where I'm trying to clean up connections after
successfully opening them. The problem is that if I try to close a
connection
that has already been closed, I get an error (because 'getConnection' cannot
find it). But then there's no way for me to find out if a connection has
already been closed. Perhaps there's another approach I should be taking?
The
context is basically,
con - file(foo, w)
tryCatch({
## Do stuff that might fail
writeLines(stuff, con)
close(con)
file.copy(foo, bar)
}, finally = {
close(con)
})
This doesn't address isOpen, but why do you have the call to close
inside the tryCatch block? Isn't the idea that finally will always be
run and so you can be reasonably sure that close gets called once?
If your real world code is more complicated, perhaps you can make use
of a work around like:
myIsOpen = function(con) tryCatch(isOpen(con), error=function(e) FALSE)
You could do similar with myClose and close a connection as many
times as you'd like :-)
+ seth
--
Seth Falcon | [EMAIL PROTECTED] | blog: http://userprimary.net/user/
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