I broke it. Segmentation fault...

[Sean Charles]

Hi,

I have been trying to run some code against "/var/log/system.log" on my iMac, which is currently 6.4M which is not *that* big. Having first exhausted the 32K default global stack I re-ran it with:

$ GLOBALSZ=128000 gprolog

and this predicate works:

    file('/var/log/system.log',X).

but this one doesn't, resulting in a segfault after a few seconds:

    file_get_contents('/var/log/system.log',X).

| ?- file_get_contents('/var/log/system.log',X).

Segmentation fault: 11

bash-3.2$

I have no doubt it is to do with the way my code is structured so I wondered what improvements I could make. I am currently trying to lex and parse a file but first I wanted to get comfortable with ways of loading files as part of my learning.

Here is my code, comments removed for brevity… the borked predicate first...

file_get_contents(Filename, Contents) :-

        open(Filename, read, F),

        fgc_read(F, [], Data),

        close(F),

        reverse(Data, Contents).

fgc_read(F, Acc, Acc) :- at_end_of_stream(F), !.

fgc_read(F, Acc, Contents) :-

    get_char(F, Chr),

    fgc_read(F, [Chr | Acc], Contents).

And the code for the predicate that manages to complete with the increased memory available...

file(Filename, Lines) :-

        file_get_contents(Filename, F),

        file_eol(F, [], Lines).

file_eol([], Acc, Lines) :- reverse(Acc, Lines).

file_eol(Contents, Acc, Lines) :-

        until_eol(Contents, Rest, Extracted),

        file_eol(Rest, [Extracted | Acc], Lines).

until_eol([], [], []).      % nothing to extract

until_eol(['\n'|T], T, []). % on a boundary, extracted nothing.

until_eol([C|T],Acc,[C|Data]) :- until_eol(T,Acc,Data).

skip_eol(X,Y) :- until_eol(X,Y,_).

Any suggestions for efficiency improvements are more than welcome as are style tips. In the meantime I shall continue to work with GNU Prolog as it embodies the free spirit I felt when I learned to program some thirty-six years ago when I learned BASIC cassette loaded into an 8K computer (anybody remember cassettes?)

I will also try to run it under strace

Thanks,

Sean.