I have another minimal testcase. It actually doesn't exhibit a freeze like I see in my application, but it's definitely not working, so I think it's worth looking at.

The code:

(defun receive-each (connections)

  (let ((ready (usocket:wait-for-input connections :timeout 0 :ready-only t)))

    (loop for connection in ready

       collect (read-line (usocket:socket-stream connection)))))

(defun receive-all (connections)

  (loop for messages = (receive-each connections)

     then (receive-each connections)

     while messages append messages))

(defun send (connection message)

  (format (usocket:socket-stream connection) "~a~%" message)

  (force-output (usocket:socket-stream connection)))

(defun server ()

  (let* ((listen (usocket:socket-listen usocket:*wildcard-host* 12345))

         (connection (usocket:socket-accept listen)))

    (loop for messages = (receive-all connection) then (receive-all connection)

       do (format t "Got messages:~%~s~%" messages)

       do (sleep 1/50))))

(defun client ()

  (let ((connection (usocket:socket-connect "localhost" 12345)))

    (loop for i from 0

       do (send connection (format nil "This is message ~a." i))

       do (sleep 1/100))))

Here is what the output looks like on everything I've tested except SBCL on Windows. (Tested on SBCL on Mac, and Clozure CL on Windows.)

* (server)

Got messages:

("This is message 0." "This is message 1." "This is message 2.")

Got messages:

("This is message 3." "This is message 4.")

...

Here is the output on SBCL on Windows.

* (server)

Got messages:

NIL

Got messages:

NIL

...

I think in this case wait-for-input never returns anything as ready so I never read from the socket.

On Sat, Apr 30, 2011 at 1:13 AM, Elliott Slaughter <elliottslaughter@gmail.com> wrote:

Hi,

I'm wondering if there is a good way to figure out how much data is available on a socket. Right now I have a situation where my program accepts messages over a TCP socket. To check to see if a single message is available, I can just call wait-for-input with :timeout 0. But in order to check for multiple messages on a single socket, I need multiple calls to wait-for-input. So something like

(iter (for ready next (wait-for-input socket :timeout 0))

      (while (read-message socket)))

I'm avoiding multithreading to preserve compatibility with Lisps that don't support (or have unstable support for) threads.

The above works on most implementations, but breaks on SBCL/Windows, where subsequent calls to wait-for-input appear to block, despite the :timeout 0 parameter.

There may very well be a bug in the SBCL/Windows implementation in usocket to chase down here. Alternatively, is there a better way to do the above (assuming that multithread is unavailable in the implementation I want to run this on)?

Thanks.

--
Elliott Slaughter

"Don't worry about what anybody else is going to do. The best way to predict the future is to invent it." - Alan Kay

--
Elliott Slaughter

"Don't worry about what anybody else is going to do. The best way to predict the future is to invent it." - Alan Kay
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