[Rd] [External] Re: Operations with long altrep vectors cause segfaults on Windows
iuke-tier@ey m@iii@g oii uiow@@edu
iuke-tier@ey m@iii@g oii uiow@@edu
Tue Sep 8 18:37:51 CEST 2020
On Tue, 8 Sep 2020, Martin Maechler wrote:
>>>>>> luke-tierney
>>>>>> on Tue, 8 Sep 2020 09:42:43 -0500 (CDT) writes:
>
> > On Tue, 8 Sep 2020, Martin Maechler wrote:
> >>>>>>> Martin Maechler
> >>>>>>> on Tue, 8 Sep 2020 10:40:24 +0200 writes:
> >>
> >>>>>>> Hugh Parsonage
> >>>>>>> on Tue, 8 Sep 2020 18:08:11 +1000 writes:
> >>
> >> >> I can only reproduce on Windows, but reliably (both 4.0.0 and 4.0.2):
> >>
> >> >> $> R --vanilla
> >> >> x <- c(0L, -2e9:2e9)
> >>
> >> >> # > Segmentation fault
> >>
> >> >> Tried to reproduce on Linux but the above worked as expected. Not an
> >> >> issue merely with the length of the vector; for example, x <-
> >> >> rep_len(1:10, 1e10) works, though the altrep vector must be long to
> >> >> reproduce:
> >>
> >> >> x <- c(0L, -1e9:1e9) #ok
> >>
> >> >> Segmentation faults occur with the following too:
> >>
> >> >> x <- (-2e9:2e9) + 1L
> >>
> >> > Your operation would "need" (not in theory, but in practice)
> >> > to go from altrep to regular vectors.
> >> > I guess the segfault occurs because of something like this :
> >>
> >> > R asks Windows to hand it a huge amount of memory and Windows replies
> >> > "ok, here is the memory pointer"
> >> > and then R tries to write to there, but illegally (because
> >> > Windows should have told R that it does not really have enough
> >> > memory for that ..).
> >>
> >> > I cannot reproduce the segmentation fault .. but I can confirm
> >> > there is a bug there that shows for me on Windows but not on
> >> > Linux:
> >>
> >> > "My" Windows is on a terminalserver not with too many GB of memory
> >> > (but then in a version of Windows that recognizes that it cannot
> >> > get so much memory):
> >>
> >> > ------------------------- Here some transcript (thanks to
> >> > using Emacs w/ ESS also on Windows) ------------------
> >>
> >> > R Under development (unstable) (2020-08-24 r79074) -- "Unsuffered Consequences"
> >> > Copyright (C) 2020 The R Foundation for Statistical Computing
> >> > Platform: x86_64-w64-mingw32/x64 (64-bit)
> >>
> >> > R ist freie Software und kommt OHNE JEGLICHE GARANTIE.
> >> > Sie sind eingeladen, es unter bestimmten Bedingungen weiter zu verbreiten.
> >> > Tippen Sie 'license()' or 'licence()' für Details dazu.
> >>
> >> > R ist ein Gemeinschaftsprojekt mit vielen Beitragenden.
> >> > Tippen Sie 'contributors()' für mehr Information und 'citation()',
> >> > um zu erfahren, wie R oder R packages in Publikationen zitiert werden können.
> >>
> >> > Tippen Sie 'demo()' für einige Demos, 'help()' für on-line Hilfe, oder
> >> > 'help.start()' für eine HTML Browserschnittstelle zur Hilfe.
> >> > Tippen Sie 'q()', um R zu verlassen.
> >>
> >> >> x <- (-2e9:2e9) + 1L
> >> > Fehler: kann Vektor der Größe 14.9 GB nicht allozieren
> >> >> y <- c(0L, -2e9:2e9)
> >> > Fehler: kann Vektor der Größe 14.9 GB nicht allozieren
> >> >> Sys.setenv(LANGUAGE="en")
> >> >> y <- c(0L, -2e9:2e9)
> >> > Error: cannot allocate vector of size 14.9 Gb
> >> >> y <- -1e9:4e9
> >> >> .Internal(inspect(y))
> >> > @0x00000000195a6808 14 REALSXP g0c0 [REF(65535)] -1000000000 : -294967296 (compact)
> >> >> .Machine$integer.max / 1e9
> >> > [1] 2.147484
> >> >> y <- -1e6:2.2e9
> >> >> .Internal(inspect(y))
> >> > @0x000000000a11a5d8 14 REALSXP g0c0 [REF(65535)] -1000000 : -2094967296 (compact)
> >> >> y <- -1e6:2e9
> >> >> .Internal(inspect(y))
> >> > @0x000000000a13adf0 13 INTSXP g0c0 [REF(65535)] -1000000 : 2000000000 (compact)
> >> >>
> >> > ------------------------- end of transcript -----------------------------------
> >>
> >> > So indeed, no seg.fault, R notices that it can't get 15 GB of
> >> > memory.
> >>
> >> > But the bug is bad news: We have *silent* integer overflow happening
> >> > according to what .Internal(inspect(y)) shows...
> >>
> >> > .... less bad new: Probably the bug is only in the 'internal inspect' code
> >> > where a format specifier is used in C's printf() that does not work
> >> > correctly on Windows, at least the way it is currently compiled ..
> >>
> >>
> >> > On (64-bit) Linux, I get
> >>
> >> >> y <- -1e9:4e9 ; .Internal(inspect(y))
> >> > @7d86388 14 REALSXP g0c0 [REF(65535)] -1000000000 : 4000000000 (compact)
> >>
> >> >> y <- c(0L, y)
> >> > Error: cannot allocate vector of size 37.3 Gb
> >>
> >> > which seems much better ... until I do find a bug, may again
> >> > only in the C code underlying .Internal(inspect(.)) :
> >>
> >> >> y <- -1e9:2e9 ; .Internal(inspect(y))
> >> > @7d86ac0 13 INTSXP g0c0 [REF(65535)] Error: long vectors not supported yet: ../../../R/src/main/altclasses.c:139
> >> >>
> >>
> >> Indeed, the purported "integer overflow" (above) does not
> >> happen.
> >> It is "only" a 'printf' related bug inside .Internal(inspect(.)) on Windows.
> >>
> >> *interestingly*, the above bug I've noticed on (64-bit) Linux
> >> does *not* show on Windows (64-bit), at least not for that case:
> >>
> >> On Windows, things are fine as long as they remain (compacted
> >> aka 'ALTREP') INTSXP:
> >>
> >> > y <- -1e3:2e9 ;.Internal(inspect(y))
> >> @0x000000000a285648 13 INTSXP g0c0 [REF(65535)] -1000 : 2000000000 (compact)
> >> > y <- -1e3:2.1e9 ;.Internal(inspect(y))
> >> @0x0000000019925930 13 INTSXP g0c0 [REF(65535)] -1000 : 2100000000 (compact)
> >>
> >> and here, y is correct, just the printing from
> >> .Internal(inspect(y)) is bugous (probably prints the double as an integer):
>
> > It's a '%ld' that probably needs to be '%lld' for Windows. Will fix
> > sometime soon.
>
> > Best,
> > luke
>
> I had guessed at something like that .. but "interestingly" it
> was quite different:
>
> Our code use int n = LENGTH(.);
> and the error message above was triggered there.
>
> I've committed a fix to both R-devel and R-patched (and added a
> regression test),
> but I still wonder why the above error had not triggered on Windows...
It does for me without the fix, so no additional Windows quirk here at
least.
Best,
luke
>
> Martin
>
> >>
> >> > y <- -1e3:2.2e9 ; .Internal(inspect(y))
> >> @0x00000000195c0178 14 REALSXP g0c0 [REF(65535)] -1000 : -2094967296 (compact)
> >> > length(y)
> >> [1] 2200001001
> >> > tail(y)
> >> [1] 2.2e+09 2.2e+09 2.2e+09 2.2e+09 2.2e+09 2.2e+09
> >> > tail(y) - 2.2e9
> >> [1] -5 -4 -3 -2 -1 0
> >> >
> >>
> >> ______________________________________________
> >> R-devel using r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
>
> > --
> > Luke Tierney
> > Ralph E. Wareham Professor of Mathematical Sciences
> > University of Iowa Phone: 319-335-3386
> > Department of Statistics and Fax: 319-335-3017
> > Actuarial Science
> > 241 Schaeffer Hall email: luke-tierney using uiowa.edu
> > Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
>
--
Luke Tierney
Ralph E. Wareham Professor of Mathematical Sciences
University of Iowa Phone: 319-335-3386
Department of Statistics and Fax: 319-335-3017
Actuarial Science
241 Schaeffer Hall email: luke-tierney using uiowa.edu
Iowa City, IA 52242 WWW: http://www.stat.uiowa.edu
More information about the R-devel
mailing list