[3.4 backport] Fix a race condition with interned strings sweeping. #12873
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[Bug #21172] This fixes a rare CI failure. The timeline of the race condition is: - A `"foo" oid=1` string is interned. - `"foo" oid=1` is no longer referenced and will be swept in the future. - Another `"foo" oid=2` string is interned. - `register_fstring` finds `"foo" oid=1`, but since it is about to be swept, removes it from `fstring_table` and insert `"foo" oid=2` instead. - `"foo" oid=1` is swept, since it has the `RSTRING_FSTR` flag, a `st_delete` is issued in `fstring_table` which removes `"foo" oid=2`. I don't know how to reproduce this bug consistently in a single test case.
k0kubun
approved these changes
Mar 6, 2025
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[Bug #21172]
This fixes a rare CI failure.
The timeline of the race condition is:
"foo" oid=1string is interned."foo" oid=1is no longer referenced and will be swept in the future."foo" oid=2string is interned.register_fstringfinds"foo" oid=1, but since it is about to be swept, removes it fromfstring_tableand insert"foo" oid=2instead."foo" oid=1is swept, since it has theRSTRING_FSTRflag, ast_deleteis issued infstring_tablewhich removes"foo" oid=2.I don't know how to reproduce this bug consistently in a single test case.