[slime-devel] Connection to Emacs lost. condition: junk in string

[Helmut Eller]

* Kelly McDonald [2009-06-27 12:50+0200] writes:

> Helmut,
> Thanks for your reply.
> I believe what is happening is that read-sequence is running out of
> bytes to read from the socket, resulting in a top-level error, causing
> it to go back to process-requests
> which tries to decode-event on a socket that has a partially read
> packet queued up.
>
> I'm guessing that there is something that needs to be done to turn the
> socket into a somewhat friendlier stream in swank-sbcl/socket-fd so
> that you don't get the toplevel error when
> read-sequence out-runs the socket. - but that is just a guess.
>
> any pointers would be welcome!

Judging from your backtrace and assuming you have *communication-style*
set to :fd-handler, it looks indeed like read-sequence is running out of
bytes and then calls sb-sys:wait-until-fd-usable and then serve-event
which recursively calls Swank's fd-handler.

I think we have no other choice than to prevent our fd-handlers from
be called recursively.  Can you reproduce the problem and try if
it goes away with the following modification in swank-sbcl.lisp?

(defimplementation add-fd-handler (socket fn)
  (declare (type function fn))
  (let ((fd (socket-fd socket))
        (handler nil))
    (labels ((add ()
               (setq handler (sb-sys:add-fd-handler fd :input #'run)))
             (run (fd)
               (sb-sys:remove-fd-handler handler) ; prevent recursion
               (unwind-protect 
                    (funcall fn)
                 (when (sb-unix:unix-fstat fd) ; still open?
                   (add)))))
      (add))))

Helmut.