If you follow perl5-porters, you'll know this already, but I think this deserves all the exposure it can.

Long-time perl users might be aware that perl's regular expression engine is a recursive implementation. This usually work ok, except on rather pathological cases where so much recursion takes place that the C stack runs out of space and the process dies with a segmentation fault.

    perl -le '$x = "o" x shift; $x =~ s/(o?)+//g' 10000
    # Bus error: 10 (core dumped)

[download]

(if the above doesn't crash for you, just up the 10000 a bit).

Just last week, dave_the_m checked a patch into the perl source code repository that converts the algorithm used from recursive to iterative. Since then steve_p has been busily going through the bug database, closing out dozens of bugs that have been corrected due to this change. All in all it's a stunning piece of work, and Dave deserves to be congratulated for it.

The code is now in blead. Once it's settled a while, it may be backported to the maintenance track, and it will start to appear in the 5.8 series. Otherwise you'll have to wait until 5.10.

Read Dave's announcement.

• another intruder with the mooring in the heart of the Perl

In reply to The perl regular expression engine is now iterative rather than recursive by grinder

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