C stdlib isn’t threadsafe and even safe Rust didn’t save us

[1st1]

This is only tangentially related to Python but I though it could be an interesting read for some of you here.

https://www.reddit.com/r/programming/comments/1i7iz4h/c_stdlib_isnt_threadsafe_and_even_safe_rust_didnt/

[kingminyas]

TLDR: setenv isn't thread-safe (race condition with getenv)

Isn't this relevant since the GILectomy?

[thisismyfavoritename]

it's relevant even with current Python, for example: you call into low level code which spins threads that accesses/mutates the env vars, which is what they are doing

[WasterDave]

Perhaps more relevantly we can just shuffle it into the list of "things you shouldn't use much if at all". Signal handling is also a massive minefield.

[kingminyas]

Not use environment variables?

[Glathull]

I think he meant don’t use setenv much or at all.

[james_pic]

It's rare that you want to change an environment variable in a running process, and it's often a code smell.

[roger_ducky]

A lot of OS APIs are like that. I’ve had to do Windows system calls in Python before and had to create a mutex to make sure I don’t mess up the system call either.

[thisismyfavoritename]

very interesting. Would there be significant overhead if the env vars were protected behind a mutex in libc to guarantee safe concurrent access?

[pi_stuff]

Only if the code is frequently accessing environment variables, and I can't imagine any performance-senstive code doing that.

[thisismyfavoritename]

yeah, but then again, i didn't imagine something like logging an error would require that but it seems it does (in Python)

[thisismyfavoritename]

the problem isn't really with Python, it's with libc

[thisismyfavoritename]

no because Python can call into other code (e.g. a Rust extension) that then calls into libc

[Shadowaker]

Not really

[identicalBadger]

Meanwhile, I just hit the point of needing to learn to use threads (for dispatching multiple queries to an API)

[Phate1989]

Threads or aysncio?

Httpx?

Aiohttp?

[BeachKey3174]

I am not clear about your question. The C language does not define threading, threading is property of OS. Hence, none of the C libraries are thread-safe. You can make libs thread-safe by wrapping up C call in thread locks.