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