From iuke-tier@ey m@iii@g oii uiow@@edu  Tue Sep  8 16:42:43 2020
From: iuke-tier@ey m@iii@g oii uiow@@edu (iuke-tier@ey m@iii@g oii uiow@@edu)
Date: Tue, 8 Sep 2020 09:42:43 -0500 (CDT)
Subject: [Rd] [External] Re: Operations with long altrep vectors cause
 segfaults on Windows
In-Reply-To: <24407.18005.968508.796695@stat.math.ethz.ch>
References: <CAJmOi+MjsxpO+i9r57xwb5Ex+GcrECGB17GScy-_w+Y0jK6dmQ@mail.gmail.com>
 <24407.17272.770281.413960@stat.math.ethz.ch>
 <24407.18005.968508.796695@stat.math.ethz.ch>
Message-ID: <alpine.DEB.2.21.2009080941140.3141@luke-Latitude-7480>

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()' f?r Details dazu.
>
>    > R ist ein Gemeinschaftsprojekt mit vielen Beitragenden.
>    > Tippen Sie 'contributors()' f?r mehr Information und 'citation()',
>    > um zu erfahren, wie R oder R packages in Publikationen zitiert werden k?nnen.
>
>    > Tippen Sie 'demo()' f?r einige Demos, 'help()' f?r on-line Hilfe, oder
>    > 'help.start()' f?r eine HTML Browserschnittstelle zur Hilfe.
>    > Tippen Sie 'q()', um R zu verlassen.
>
>    >> x <- (-2e9:2e9) + 1L
>    > Fehler: kann Vektor der Gr??e 14.9 GB nicht allozieren
>    >> y <- c(0L, -2e9:2e9)
>    > Fehler: kann Vektor der Gr??e 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
>  >
>
> ______________________________________________
> R-devel at 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 at uiowa.edu
Iowa City, IA 52242                 WWW:  http://www.stat.uiowa.edu


[Rd] [External] Re: Operations with long altrep vectors cause segfaults on Windows
iuke-tier@ey m@iii@g oii uiow@@edu