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Postings from March 2003
David Dyck <david.dyck@fluke.com> wrote:
:The following code using Parse::RecDescent does
:an infinite loop with perl5.9.0 (presuming with 5.8.1)
:but finishes fine with perl5.8.0. I haven't simplified
:this as much as I could yet, the grammar comes
:from derived from Inline::C::ParseRecDescent, where
:I first saw the problem in its make test.
Here's another step of simplification:
#!/usr/bin/perl -w
use strict;
sub get_parser {
require Parse::RecDescent;
$main::RD_HINT++;
Parse::RecDescent->new(grammar())
}
sub grammar {
<<'END';
code: 'x' { '...' }
END
}
BEGIN { $::RD_TRACE = 1; }
get_parser()->code('x');
get_parser()->code('x');
__END__
If I copy the Parse::RecDescent module into a new file and require
that instead, the problem goes away, so I'm not sure how best to
track this down further. But the -Dr output before hitting the loop
is down to under 6K lines now, so I think it's starting to come
within reach. Just to recapitulate, the tail of that output looks
like:
Matching REx `^["'`]' against `''
Setting an EVAL scope, savestack=165
0 <> <'> | 1: BOL
0 <> <'> | 2: ANYOF["'`]
1 <'> <> | 13: END
Match successful!
Guessing start of match, REx ` \' [^\\']* (\\.[^\\']*)* \' ' against `'...']; }
'...
Found floating substr `'' at offset -243388...
Contradicts anchored substr `'', trying floating at offset -243387...
Found floating substr `'' at offset -243431...
Contradicts anchored substr `'', trying floating at offset -243430...
Found floating substr `'' at offset -243431...
Contradicts anchored substr `'', trying floating at offset -243430...
[loop]
The construction of the string also seems important: if I replace the
grammar with the (theoretically identical):
sub grammar {
q[code: 'x' { '...' }
]
}
.. it no longer fails. I suspect this is down to malloc perturbation,
since various small changes can cause it to stop failing either with
or without -Dr, or both.
Hugo