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From: Dr.Ruud on 27 Jun 2010 05:42 Willem wrote: > AFAIK, when you call <map> in void context, it turns into a <for> internally. Don't think that. For example, in some older versions of Perl, a map inside a map only releases memory in the outsidest map, which can make things horrible. -- Ruud
From: Ilya Zakharevich on 27 Jun 2010 19:45 On 2010-06-26, C.DeRykus <derykus(a)gmail.com> wrote: > On Jun 25, 11:16�pm, Ilya Zakharevich <nospam-ab...(a)ilyaz.org> wrote: >> On 2010-06-26, C.DeRykus <dery...(a)gmail.com> wrote: >> >> > � � � () = <>; >> >> Try to do it with a terabyte file... >> > > Hm, sounds like I need to look more closely... > > So a humongous temp array gets built with only > the resulting assignment being optimized away...? Hmm, IN PRINCIPLE, one could have coded recognition of this construct, and would somehow advise pp_readline() that its output is going to be ignored. However, given the frequency of this construct, I doubt this was ever done. > perl -MO=Concise -e "()=<>" > 8 <@> leave[1 ref] vKP/REFC ->(end) > 1 <0> enter ->2 > 2 <;> nextstate(main 1 -e:1) v:{ ->3 > 7 <2> aassign[t3] vKS ->8 > - <1> ex-list lK ->6 > 3 <0> pushmark s ->4 > 5 <1> readline[t2] lK/1 ->6 > 4 <#> gv[*ARGV] s ->5 > - <1> ex-list lK ->7 > 6 <0> pushmark s ->7 > - <0> stub lPRM* ->- The only way I know to advise an OP is via flags. So one should compare flags on the `readline' OP with those on "usual" list contents readline. If they are identical, there is little chance that this construct is memory-optimized. (But they may differ by "other reasons" as well...) Yours, Ilya
From: Ilya Zakharevich on 27 Jun 2010 19:53 On 2010-06-26, Willem <willem(a)turtle.stack.nl> wrote: > I don't know if <> is smart enough to recognize void context though, > can probably be tested with a large file and a memory checker tool. I use void-context-<> all the time (to skip one line); but only with defined $/. I vaguely remember that about 10 years ago, I put some code to optimize behaviour of pp_readline() in void context (or at least, had a WISH to do so; no way to distinguish now, sigh). And, definitely, about the same time I had the same problem as the OP: avoiding SIGPIPE on the OTHER side of the pipe. Putting 2 and 2 together, I MIGHT have put there optimization-of-<>-with-undefined-$/-in-void-context. But no, I have no memory of actually doing it. And I have strong doubts about somebody else doing it as well... So I think it is not wise to expect that the core of Perl would be able to help with this problem. I would just do $/ = (1<<20), and do a loop. Hope this helps, Ilya
From: Ilya Zakharevich on 27 Jun 2010 19:56 On 2010-06-27, Willem <willem(a)turtle.stack.nl> wrote: > ) void context always translates to scalar context for built-in functions. > ) > ) void context usually translates to scalar context for user-defined functions. > What about map ? > AFAIK, when you call <map> in void context, it turns into a <for> internally. Irrelevant: SIDE EFFECTS of map in scalar and list context are the same. Hope this helps, Ilya
From: John Kelly on 27 Jun 2010 20:41
On Sun, 27 Jun 2010 23:53:10 +0000 (UTC), Ilya Zakharevich <nospam-abuse(a)ilyaz.org> wrote: >I had the same problem as the OP: avoiding SIGPIPE >on the OTHER side of the pipe. >So I think it is not wise to expect that the core of Perl would be >able to help with this problem. I would just do $/ = (1<<20), and do >a loop. I went with the loop. (1<<20) is a 1 meg of memory. (1<<15) may run nearly as fast on a large file (untested). -- Web mail, POP3, and SMTP http://www.beewyz.com/freeaccounts.php |