[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 16:42:43 CEST 2020
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):
>
> >> $> R --vanilla
> >> x <- c(0L, -2e9:2e9)
>
> >> # > Segmentation fault
>
> >> Tried to reproduce on Linux but the above worked as expected. Not an
> >> issue merely with the length of the vector; for example, x <-
> >> rep_len(1:10, 1e10) works, though the altrep vector must be long to
> >> reproduce:
>
> >> x <- c(0L, -1e9:1e9) #ok
>
> >> Segmentation faults occur with the following too:
>
> >> x <- (-2e9:2e9) + 1L
>
> > Your operation would "need" (not in theory, but in practice)
> > to go from altrep to regular vectors.
> > I guess the segfault occurs because of something like this :
>
> > R asks Windows to hand it a huge amount of memory and Windows replies
> > "ok, here is the memory pointer"
> > and then R tries to write to there, but illegally (because
> > Windows should have told R that it does not really have enough
> > memory for that ..).
>
> > I cannot reproduce the segmentation fault .. but I can confirm
> > there is a bug there that shows for me on Windows but not on
> > Linux:
>
> > "My" Windows is on a terminalserver not with too many GB of memory
> > (but then in a version of Windows that recognizes that it cannot
> > get so much memory):
>
> > ------------------------- Here some transcript (thanks to
> > using Emacs w/ ESS also on Windows) ------------------
>
> > R Under development (unstable) (2020-08-24 r79074) -- "Unsuffered Consequences"
> > Copyright (C) 2020 The R Foundation for Statistical Computing
> > Platform: x86_64-w64-mingw32/x64 (64-bit)
>
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>
> >> x <- (-2e9:2e9) + 1L
> > Fehler: kann Vektor der Größe 14.9 GB nicht allozieren
> >> y <- c(0L, -2e9:2e9)
> > Fehler: kann Vektor der Größe 14.9 GB nicht allozieren
> >> Sys.setenv(LANGUAGE="en")
> >> y <- c(0L, -2e9:2e9)
> > Error: cannot allocate vector of size 14.9 Gb
> >> y <- -1e9:4e9
> >> .Internal(inspect(y))
> > @0x00000000195a6808 14 REALSXP g0c0 [REF(65535)] -1000000000 : -294967296 (compact)
> >> .Machine$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
>
> > 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
> >
>
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--
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
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