[Rd] save() and interrupts
luke at stat.uiowa.edu
Mon Apr 16 21:23:15 CEST 2007
On Mon, 16 Apr 2007, Bill Dunlap wrote:
> On Sun, 15 Apr 2007, Henrik Bengtsson wrote:
>> On 4/15/07, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
>>> On Sun, 15 Apr 2007, Henrik Bengtsson wrote:
>>>> are there any (cross-platform) specs on what the saved filed is if
>>>> save() is interrupted, e.g. by a user interrupt? It could be
>>>> non-existing, empty, partly written, or completed.
>>> My understanding is that you cannot user interrupt compiled code unless it
>>> is set up to check interrupts. Version 2 saves are done via the internal
>>> saveToConn, and I don't see any calls to R_CheckUserInterrupt there. So
>>> you only need to worry about user interrupts in the R code, and that has
>>> an on.exit action to close the connection (which should be executed even
>>> if you interrupt). Which suggests that the file will be
>>> and the first two depend on interrupting in the millisecond or less before
>>> the compiled code gets called.
>> I'll put it on my todo list to investigate how to make save() more
>> robust against interrupts before calling the internal code. One
>> option is to use tryCatch(). However, that does not handle too
>> frequent user interrupts, e.g. if an interrupt is sent while in the
>> "interrupt" call, that will interrupt the function. So, tryCatch()
>> alone will only lower the risk for incomplete empty files. For data
>> written to files, one alternative is to check for files of zero size
>> in the on.exit() statement and remove such.
>>> For other forms of interrupts, e.g. a Unix kill -9, the file state could
>>> be anything.
>>> Brian D. Ripley, ripley at stats.ox.ac.uk
> You could change the code to write to a temporary
> file (in the directory you want the result in) and
> when you successfully finish writing to the file
> you rename it to the permanent name. (On an interrupt
> you remove the temp file, and on 'kill -9' the only
> bad effect is the space used by the partially written
> temp file.) This has the added advantage that you don't
> overwrite an existing save file by the given name until
> you know a suitable replacement is ready.
> Perhaps we need a connection type that encapsulates this.
> Bill Dunlap
> Insightful Corporation
> bill at insightful dot com
> "All statements in this message represent the opinions of the author and do
> not necessarily reflect Insightful Corporation policy or position."
We do this with save.image. Since save is a little more general it is
a bit less obvious what the right way to do this sort of thing is, or
whether there is a single right way. I think if I was concerned about
this I would write something around the current save for particular
kinds of connections rather than changing save itself. The main
reason for taking a different rout with save.image is that that gets
called implicitly by q().
[our current ability to manage user interrupts is not ideal--hopefully
we can make a bit of progress on this soon.]
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