New submission from Gregory P. Smith <g...@krypto.org>:
The underlying API calls made by os.putenv() and os.environ[name] = value syntax are not thread safe on POSIX systems. POSIX _does not have_ any thread safe way to access the process global environment. In a pure Python program, the GIL prevents this from being an issue. But when embedded in a C/C++ program or using extension modules that launch their own threads from C, those threads could also make the invalid assumption that they can safely _read_ the environment. Which is a race condition when a Python thread is doing a putenv() at the same time. We should document the danger. CPython's os module snapshots a copy of the environment into a dict at import time (during CPython startup). But os.environ[] assignment and os.putenv() modify the actual process global environment in addition to updating this dict. (If an embedded interpreter is launched from a process with other threads already running, even that initial environment reading could be unsafe if the larger application has a thread that wrongly assumes it has exclusive environment access) For people modifying os.environ so that the change is visible to child processes, we can recommend using the env= parameter on subprocess API calls to supply a new environment. A broader issue of should we be modifying the process global environment state at all from os.putenv() and os.environ[] assignment still exists. I'll track that in another issue (to be opened). ---------- assignee: docs@python components: Documentation messages: 360221 nosy: docs@python, gregory.p.smith priority: normal severity: normal status: open title: Document os.environ[x] = y and os.putenv() as thread unsafe versions: Python 2.7, Python 3.7, Python 3.8, Python 3.9 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue39375> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
