Up to now there is no thread way to read the umask in Python

https://stackoverflow.com/questions/53227072/reading-umask-thread-safe

You can use this pattern:

current_umask = os.umask(0)  # line1
os.umask(current_umask)      # line2
return current_umask

A thread which executes between line1 and line2 will have a different umask.

I would be great, if the python standard library would provide correspondig thread safe method.

Related question at stackoverflow: https://stackoverflow.com/questions/53227072/reading-umask-thread-safe

There is no thread way to read the umask in C as well. The os module provides thin wrappers to the POSIX API. os.umask() acts exactly as a C function umask(). If thread safe method be added in the POSIX API we can expose it in the os module.

Maybe the Python documentation can be enhanced to document functions which are known to have a side-effect "process-wide" vs "thread-safe" functions. For example, signal.pthread_sigmark() affects the current thread, wheras locale.setlocale() is process-wide.

See "POSIX Safety Concepts" of the glibc:

https://www.gnu.org/software/libc/manual/html_node/POSIX-Safety-Concepts.html#POSIX-Safety-Concepts

Example with setlocale, "MT-Unsafe":

https://www.gnu.org/software/libc/manual/html_node/Setting-the-Locale.html

My own (incomplete) list of "process-wide states":
https://vstinner.readthedocs.io/threads.html#process-wide

Ok, let's move to bpo-35276: "Document thread safety".