[Python-Dev] new failing test -- test_compiler (original) (raw)

Armin Rigo arigo at tunes.org
Sun Aug 8 00:23:57 CEST 2004

Hi,

On Sat, Aug 07, 2004 at 09:47:22PM +0100, Michael Hudson wrote:

k = '' for node in nodelist: k += self.decodeliteral(node[1])

what does this make you think of? Yes, it's the new += string optimizations; Python gets upset if you mutate interned strings... Armin is on the case...

Ahem, oups, yes, I am to blame for this memory corruption bug. In the += string optimization I forgot that the string's ob_refcnt field is not always "correct". String interning messes with its value. What occurred here is that we mutated a string which had only one reference left -- that is, one apart from the two that stringobject.c artificially removes to ob_refcnt when interning.

This is now fixed by skipping the optimization if we got an interned string.
While messing with ob_refcnt is always a bit fragile I am still convinced that the += optimization is safe again.

A bientôt,

Armin.

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