FD_RENUMBER

Atomically replace a file descriptor by renumbering another file descriptor.

Due to the strong focus on thread safety, this environment does not provide a mechanism to duplicate or renumber a file descriptor to an arbitrary number, like dup2(). This would be prone to race conditions, as an actual file descriptor with the same number could be allocated by a different thread at the same time.

This function provides a way to atomically renumber file descriptors, which would disappear if dup2() were to be removed entirely.

(@interface func (export "fd_renumber")
  (param $fd $fd)
  ;;; The file descriptor to overwrite.
  (param $to $fd)
  (result $error (expected (error $errno)))
)