BUG: Fix Memory Leak in read_csv

[Alvaro-Kothe]

• closes Read_csv leaks memory when used in multiple threads #19941 (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.
• I have reviewed and followed all the contribution guidelines
• If I used AI to develop this pull request, I prompted it to follow AGENTS.md.

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I used the reproduction from #19941 (comment) to start solving the problem, after solving that, couldn't reproduce the original issue with the ThreadPool.

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Reproduction

import io
from pandas import read_csv

s = """item_id,user_id,region,city,parent_category_name,category_name,param_1,param_2,param_3,title,description,price,item_seq_number,activation_date,user_type,image,image_top_1,deal_probability
ba83aefab5dc,91e2f88dd6e3,Ростовская область,Ростов-на-Дону,Бытовая электроника,Аудио и видео,"Видео, DVD и Blu-ray плееры",,,Philips bluray,"В хорошем состоянии, домашний кинотеатр с blu ray, USB. Если настроить, то работает смарт тв Торг",4000.0,9,2017-03-20,Private,b7f250ee3f39e1fedd77c141f273703f4a9be59db4b48a8713f112c67e29bb42,3032.0,0.43177"""

buf = io.StringIO(s)

read_csv(buf)

LSan report:

Direct leak of 39 byte(s) in 1 object(s) allocated from:
    #0 0x0000004a9478 in malloc (/home/alvaro/opt/python-asan/bin/python3.14+0x4a9478) (BuildId: d34f3059a20abaa7865a706a3f4007981ffba2c9)
    #1 0x0000005d2e72 in _PyBytes_FromSize /home/alvaro/opt/Python-3.14.6/Objects/bytesobject.c:125:31
    #2 0x0000005d2e72 in PyBytes_FromStringAndSize /home/alvaro/opt/Python-3.14.6/Objects/bytesobject.c:155:27
    #3 0x0000007acdb8 in unicode_encode_utf8 /home/alvaro/opt/Python-3.14.6/Objects/unicodeobject.c:5865:16
    #4 0x0000007ad565 in _PyUnicode_AsUTF8String /home/alvaro/opt/Python-3.14.6/Objects/unicodeobject.c:5954:12
    #5 0x0000007ad565 in PyUnicode_AsEncodedString /home/alvaro/opt/Python-3.14.6/Objects/unicodeobject.c:3959:24
    #6 0x000000807aae in unicode_encode_impl /home/alvaro/opt/Python-3.14.6/Objects/unicodeobject.c:11867:12
    #7 0x000000807aae in unicode_encode /home/alvaro/opt/Python-3.14.6/Objects/clinic/unicodeobject.c.h:293:20
    #8 0x0000005f642b in _PyObject_VectorcallTstate /home/alvaro/opt/Python-3.14.6/./Include/internal/pycore_call.h:177:11
    #9 0x0000005f642b in PyObject_VectorcallMethod /home/alvaro/opt/Python-3.14.6/Objects/call.c:918:18
    #10 0x7b6b428ebd45 in __pyx_pf_6pandas_5_libs_7parsers_10TextReader___cinit__ /home/alvaro/projects/oss/pandas/build/clang-asan/pandas/_libs/parsers.cpython-314-x86_64-linux-gnu.so.p/pandas/_libs/parsers.pyx.c:7861:19
    #11 0x7b6b428e7ea2 in __pyx_pw_6pandas_5_libs_7parsers_10TextReader_1__cinit__ /home/alvaro/projects/oss/pandas/build/clang-asan/pandas/_libs/parsers.cpython-314-x86_64-linux-gnu.so.p/pandas/_libs/parsers.pyx.c:7785:13
    #12 0x7b6b428be7c8 in __pyx_tp_new_6pandas_5_libs_7parsers_TextReader /home/alvaro/projects/oss/pandas/build/clang-asan/pandas/_libs/parsers.cpython-314-x86_64-linux-gnu.so.p/pandas/_libs/parsers.pyx.c:31489:16
    #13 0x00000075ccfe in type_call /home/alvaro/opt/Python-3.14.6/Objects/typeobject.c:2372:11
...

SUMMARY: AddressSanitizer: 39 byte(s) leaked in 1 allocation(s).

[jbrockmendel]

should this be bytes?

[Alvaro-Kothe]

No, it should be an object.

The element that PyBytes_AsString receives is an object. And the goal of this member is to keep a valid reference for self.encoding_errors.

[jbrockmendel]

ehh, can do this in a separate step

[jbrockmendel]

thanks @Alvaro-Kothe