Is os.File's Write() threadsafe?

Question

I was wondering if calling Write() on an os.File is thread safe. I'm having a hard time finding any mention of thread safety in the docs.

Answer 1

The convention (at least for the standard library) is the following: No function/method is safe for concurrent use unless explicitly stated (or obvious from the context).

It is not safe to write concurrently to an os.File via Write() without external synchronization.

Answer 2

After browsing the source code a little bit I found the following method which is eventually called by file.Write(). Since there are race condition checks in place, I'm assuming that the call is in fact not thread-safe within Go (Source).

However, it seemed unlikely that those system calls wouldn't be thread-safe on an OS level. After some browsing I came upon this interesting answer that fueled my suspicions even more. For windows the source indicates a call to WriteFile which also appears to be thread safe.