Dear Peter,
Thank you very much for your kind and helpful reply.
As I mentioned in a followup email to r-bugs, indeed, one aspect of this
issue is a (user specified) shorter stack than that expected by R -- I
had only allowed 1 MB of stack space a long long time ago, and forgotten
about it.
Due to a glitch with [EMAIL PROTECTED], I ended up submitting this
bug twice, and your original response was attached to (PR#7827), which
Prof Brian Ripley moved to the trashcan, as was appropriate.
I've taken the liberty of responding to PR#7826 (including your reply,
below) to have your helpful response (specifically, the unclass
suggestion) associated with the representative bug number.
/Jskud
>------ Begin Included Message ------
> To: [EMAIL PROTECTED]
> Cc: r-devel@stat.math.ethz.ch, [EMAIL PROTECTED]
> Subject: Re: [Rd] segfault during build of 2.1.0 on RH9; print.POSIXct
> implicated (PR#7827)
> From: Peter Dalgaard <[EMAIL PROTECTED]>
> Date: 30 Apr 2005 12:18:56 +0200
> Lines: 73
>
> [EMAIL PROTECTED] writes:
> > > unusual_but_ok <- c.POSIXlt(character(0))
> > > unusual_but_ok
> > character(0)
> > > unusual_and_faults <- c.POSIXct(character(0))
> > > unusual_and_faults
> > Segmentation fault
> >
> > Running this test program under gdb, we find that we're running off the
> > end of the stack, with 4222 stack frames showing -- apparently in an
> > infinite recursion -- "as.character" shows up every 69 function calls:
>
> This gives a protection stack overflow on FC3 and RH8. Is the stack
> particularly small on RH9? I have 8MB on RH8 and 10MB on FC3. (The R
> limits for expression depth and pointer protection were increased in
> 2.1.0). I can force a segfault, but only after "ulimit -s 1024" or so.
>
> > #64 0x080ea1ef in Rf_usemethod (generic=0x81c8b12 "as.character", obj=0x0,
> > call=0x85a04f4,
> ...
> > So it would seem that *printing* the unusual POSIXct value is suspect.
>
> Pretty obviously, yes.
>
> > Looking at a R-1.8.1 install, we find these definitions in base/R/base:
> >
> > print.POSIXct <- function(x, ...)
> > {
> > print(format(x, usetz=TRUE), ...)
> > invisible(x)
> > }
> >
> > print.POSIXlt <- function(x, ...)
> > {
> > print(format(x, usetz=TRUE), ...)
> > invisible(x)
> > }
> >
> > However, looking at the 2.1.0 src file
> > R-2.1.0/src/library/base/R/datetime.R, we find
> >
> > print.POSIXct <- function(x, ...)
> > {
> > print(format(x, usetz=TRUE, ...), ...)
> > invisible(x)
> > }
> >
> > print.POSIXlt <- function(x, ...)
> > {
> > print(format(x, usetz=TRUE), ...)
> > invisible(x)
> > }
> >
> > Note the suspicious definition of print.POSIXct using *two* sets of
> > ellipses, and that the print.POSIXct and print.POSIXlt definitions no
> > longer match.
>
> Probably both should use the double ellipses, but "..." will be empty
> on automatic printing, so that's not it.
>
> The issue is an infinite recursion inside as.POSIXlt(). Specifically,
> strptime() internally calls as.character(x) inside the fromchar()
> function in as.POSIXlt(), and as.character.POSIXt() invokes format()
> which calls as.POSIXlt() again.
>
> I think the fix is to unclass(x) inside fromchar(), but perhaps others
> know better?
>
>
> --
> O__ ---- Peter Dalgaard Blegdamsvej 3
> c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
> (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
> ~~~~~~~~~~ - ([EMAIL PROTECTED]) FAX: (+45) 35327907
>
>------ End Included Message ------
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