New submission from Christian Heimes <li...@cheimes.de>:
is_valid_fd() uses dup() or fstat() to check whether an fd is valid. Both operations are costly. fcntl() with F_GETFD returns the file descriptor flags (e.g. CLOEXEC) and -1 with errno set to EBADF when fd is not an open file descriptor. It's faster than duplicating + closing a fd or calling fstat(). The idea to use fcntl(fd, F_GETFD) is inspired by the patch [1]. According to Stackoverflow [2]: > fcntl(fd, F_GETFD) is the canonical cheapest way to check that fd is a valid > open file descriptor. > F_GETFD is cheaper in principle since it only dereferences the > (process-local) file descriptor in kernel space, not the underlying open file > description (process-shared) which it refers to. [1] https://github.com/singlestore-labs/cpython/commit/0364554615c79b9364a0acf3038147a999ea2219 [2] https://stackoverflow.com/questions/12340695/how-to-check-if-a-given-file-descriptor-stored-in-a-variable-is-still-valid ---------- components: C API messages: 407197 nosy: christian.heimes, vstinner priority: normal severity: normal status: open title: Use fcntl(fd, F_GETFD) to check whether an fd is valid type: behavior versions: Python 3.11 _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue45915> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
