Deciding when to adjust the window size

[JCA]

    What is the algorithm adopted by OpenSSH when it comes to deciding
when to adjust the size of window? I would have thought that one'd
better adjust the window size as soon as it has fallen below the
maximum packet size. What worries me is a potential deadlock, in which
one party does not send anything, because the window is too small for
its next window space-consuming packet, while the other does not
adjust the window on the grounds that it reckons it size still is
large enough. How are such situations avoided?