fork/exec & close file descriptors

[random832 at fastmail.us]

On Wed, Jun 3, 2015, at 10:43, Marko Rauhamaa wrote:
> However, the child process needs to be prepared for os.close() to block
> indefinitely because of an NFS problem or because SO_LINGER has been
> specified by the parent, for example. Setting the close-on-exec flag
> doesn't help there.

Out of curiosity, does exec block in this situation?