[Python-checkins] bpo-45061: Detect refcount bug on empty string singleton (GH-28504)

[Marc-Andre Lemburg]

On 22.09.2021 11:24, Victor Stinner wrote:
> Hi,
> 
> I'm no longer sure why I did this change. So I just reverted it:
> https://github.com/python/cpython/pull/28516/files

Great :-) Thanks, Victor !

> Victor
> 
> On Wed, Sep 22, 2021 at 9:44 AM Marc-Andre Lemburg <mal at egenix.com> wrote:
>>
>> On 21.09.2021 23:43, vstinner wrote:
>>> bpo-45061: Detect refcount bug on empty string singleton (GH-28504)
>>>
>>> Detect refcount bugs in C extensions when the empty Unicode string
>>> singleton is destroyed by mistake.
>>>
>>> * Move forward declarations to the top of unicodeobject.c.
>>> * Simplifiy unicode_is_singleton().
>>>
>>> @@ -1982,11 +1994,8 @@ unicode_is_singleton(PyObject *unicode)
>>>      if (unicode == state->empty_string) {
>>>          return 1;
>>>      }
>>> -    PyASCIIObject *ascii = (PyASCIIObject *)unicode;
>>> -    if (ascii->state.kind != PyUnicode_WCHAR_KIND && ascii->length == 1)
>>> -    {
>>> -        Py_UCS4 ch = PyUnicode_READ_CHAR(unicode, 0);
>>> -        if (ch < 256 && state->latin1[ch] == unicode) {
>>> +    for (Py_ssize_t i = 0; i < 256; i++) {
>>> +        if (unicode == state->latin1[i]) {
>>>              return 1;
>>>          }
>>>      }
>>
>> Why are you replacing a single pointer comparison with a loop over
>> 256 comparisons ?
>>
>> That doesn't strike me as a simplification. It's just takes longer.
>>
>> --
>> Marc-Andre Lemburg
>> eGenix.com
>>
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> 
> 

-- 
Marc-Andre Lemburg
eGenix.com

Professional Python Services directly from the Experts (#1, Sep 22 2021)
>>> Python Projects, Coaching and Support ...    https://www.egenix.com/
>>> Python Product Development ...        https://consulting.egenix.com/
________________________________________________________________________

::: We implement business ideas - efficiently in both time and costs :::

   eGenix.com Software, Skills and Services GmbH  Pastor-Loeh-Str.48
    D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg
           Registered at Amtsgericht Duesseldorf: HRB 46611
               https://www.egenix.com/company/contact/
                     https://www.malemburg.com/