base.py 文件源码

def set_nonblocking(fd):
    """
    Sets the descriptor to be nonblocking.  Works on many file-like
    objects as well as sockets.  Only sockets can be nonblocking on
    Windows, however.
    """
    try:
        setblocking = fd.setblocking
    except AttributeError:
        # fd has no setblocking() method. It could be that this version of
        # Python predates socket.setblocking(). In that case, we can still set
        # the flag "by hand" on the underlying OS fileno using the fcntl
        # module.
        try:
            import fcntl
        except ImportError:
            # Whoops, Windows has no fcntl module. This might not be a socket
            # at all, but rather a file-like object with no setblocking()
            # method. In particular, on Windows, pipes don't support
            # non-blocking I/O and therefore don't have that method. Which
            # means fcntl wouldn't help even if we could load it.
            raise NotImplementedError("set_nonblocking() on a file object "
                                      "with no setblocking() method "
                                      "(Windows pipes don't support non-blocking I/O)")
        # We managed to import fcntl.
        fileno = fd.fileno()
        orig_flags = fcntl.fcntl(fileno, fcntl.F_GETFL)
        new_flags = orig_flags | os.O_NONBLOCK
        if new_flags != orig_flags:
            fcntl.fcntl(fileno, fcntl.F_SETFL, new_flags)
    else:
        # socket supports setblocking()
        setblocking(0)