sender ......

main = do
         fd <- mqOpen "/myipc" ReadWrite (Just nullFileMode) (Just (MQAttributes 0 128 128 0))
         mqSend fd "Hello world" 11 1
         (MQAttributes flags maxMsgNum maxMsgSize curNumMsgs) <- mqGetAttributes fd
         putStrLn ("attrs flags->" ++ (show flags) ++ " maxMsgNum -> " ++ (show maxMsgNum) ++ " maxMsgSize -> " ++ (show maxMsgSize) ++ " curNumMsgs -> " ++ (show curNumMsgs))
         mqClose fd
         return fd
~

-----------------------------------------

receiver

main = do
         fd <- mqOpen "/myipc" ReadWrite (Just nullFileMode) (Just (MQAttributes 0 128 128 0))
         (MQAttributes flags maxMsgNum maxMsgSize curNumMsgs) <- mqGetAttributes fd
         putStrLn ("attrs flags->" ++ (show flags) ++ " maxMsgNum -> " ++ (show maxMsgNum) ++ " maxMsgSize -> " ++ (show maxMsgSize) ++ " curNumMsgs -> " ++ (show curNumMsgs))
         (MQAttributes flags maxMsgNum maxMsgSize curNumMsgs) <- mqSetAttributes fd (MQAttributes{flags=0, maxMsgNum=127, maxMsgSize=127, curNumMsgs=7})
         putStrLn ("attrs flags->" ++ (show flags) ++ " maxMsgNum -> " ++ (show maxMsgNum) ++ " maxMsgSize -> " ++ (show maxMsgSize) ++ " curNumMsgs -> " ++ (show curNumMsgs))
         (s, n) <- mqReceive fd 60 Nothing
         putStrLn ("dump " ++ s)
         (s, n) <- mqReceive fd 11 (Just 1)
         putStrLn s
         mqClose fd
--         mqUnlink "/myipc"
         return fd
~

---------------------------------------------------------------------------------------------------------------------------------------------

Thanks, Vasili

On Sat, May 10, 2008 at 4:09 PM, Brandon S. Allbery KF8NH <allbery@ece.cmu.edu> wrote:

On 2008 May 10, at 16:47, Galchin, Vasili wrote:

Last night I sent out an announcement about some POSIX work that I have been doing. In any case, one of the FFI wrappers is driving me crazy, i.e. the one for mq_receive:http://opengroup.org/onlinepubs/007908799/xsh/mq_receive.html . When I call this function (mqReceive), I get "message too long". In my test cases I am sending and receiving messages that are only 11 bytes! The wrapper seems really straightforward. Perhaps I am looking right at the problem and don't see. I need other eyes on the wrapper to help me ;^). Please see below.

What's the other end sending?

I suspect most implementations of mq_receive() layer it on top of msgrcv(), which can return E2BIG (== EMSGSIZE) if the message to be received is larger than the receiving buffer --- a condition which I note mq_receive() does not document (unless mq_msgsize means a given queue only supports fixed size messages, which seems odd).

--
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com

system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu

electrical and computer engineering, carnegie mellon university KF8NH