Thread-unsafe libc functions

Bug report

There are a a few non thread-safe libc functions used in Python that can be an issue for free threading, isolated subinterpreters, or sometimes even with the GIL.

In https://github.com/python/cpython/issues/126316, @vstinner fixed the use setgrent / getgrent. It's probably a good time to look for other similar issues.

clang-tidy

clang-tidy has a concurrency-mt-unsafe check that looks for "known-to-be-unsafe functions".

./configure -C --with-pydebug --disable-gil

# generate compile_commands.json
bear -- make -j 

run-clang-tidy-18 -checks='-*,concurrency-mt-unsafe' -p .

Unsafe libc functions

• localeconv(): not thread-safe, see glibc's manual. Is nl_langinfo a substitue?
• setlocale
• setpwent, getpwent, and endpwent in pwdmodule.c. These are similar to grpmodule.c and can likely be addressed the same way.
• getservbyname, getservbyport, getprotobyname in Modules/socketmodule.c: use getservbyname_r, etc.? Note these thread-safety issues affect the default build because we release the GIL around the relevant calls.
• dbm_open, dbm_close, etc. in Modules/_dbmmodule.c
• getlogin: use getlogin_r if available?

Unfixable by us?

• getenv, setenv, unsetenv, putenv: environment modification isn't thread-safe and getenv is used extensively in other C libraries, so putting a lock around our accesses doesn't do much. (Might finally be fixed in glibc, see https://inbox.sourceware.org/libc-alpha/cover.1722193092.git.fweimer@redhat.com/).
• login_tty: not sure it matters as login_tty is usually called after a fork()

Safe due to our usage

• getc_unlocked, safe because we use it within a flockfile() call.
• mbrtowc() - safe as long as the passed in mbstate_t * is non-NULL, which is the case in CPython.

Safe in glibc

These functions are flagged by clang-tidy because they are not guaranteed to be safe by POSIX, but they are safe in glibc. It'd be nice to verify that they are safe in other libc implementations. I don't think it's worth changing them:

• dlerror()
• strerror(): see https://man7.org/linux/man-pages/man3/strerror.3.html
• system(): see https://man7.org/linux/man-pages/man3/system.3.html
• readdir(DIR *dirp): see https://man7.org/linux/man-pages/man3/readdir.3.html: "...in modern implementations (including the glibc implementation), concurrent calls to readdir() that specify different directory streams are thread-safe."
• wcstombs: see https://man7.org/linux/man-pages/man3/wcstombs.3.html
• nl_langinfo: https://www.man7.org/linux/man-pages/man3/nl_langinfo.3.html (as long as locale doesn't change)
• tcsendbreak, tcflow: see https://www.man7.org/linux/man-pages/man3/termios.3.html#ATTRIBUTES
• setlogmask: safe since glibc 2.33
• strsignal: not documented as thread-safe, but uses glibc uses TLS internally since 2.32

Other

• exit(): apparently concurrent calls to exit() are not thread-safe, but I don't think it matters for our usages.
• ptsname(): we already use ptsname_r(), but the static analyzer gets confused

Linked PRs

• gh-132591
• gh-132748
• gh-132749
• gh-132750
• gh-132751
• gh-135097
• gh-135098
• gh-139996

Trước tiên, hãy xem xét các PR được liên kết, sau đó kiểm tra kết quả clang-tidy concurrency-mt-unsafe cho Modules/pwdmodule.c, Modules/socketmodule.c và Modules/_dbmmodule.c. Chạy lệnh clang-tidy được ghi trong tài liệu sau khi cấu hình với --disable-gil; công việc được xem là hoàn tất khi mỗi chỗ sử dụng libc liên quan đã được xử lý hoặc tính an toàn của nó đã được giải thích thỏa đáng.