[Rd] save() and interrupts

[Bill Dunlap]

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
> >
> > non-existent
> > empty
> > complete
> >
> > 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.
>
> /Henrik
> >
> > 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.

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

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