the existing file descriptor. Instead, let dup2() atomically close the
old file descriptor when assigning the newly opened file to the same
descriptor. This closes a race in a multithreaded application where a
concurrent open() could allocate the existing file descriptor in between
the calls to close() and dup2().
PR: threads/79887
Submitted by: Dmitrij Tejblum tejblum of yandex-team.ru
Reviewed by: davidxu
MFC after: 1 week
cc3d85727d