Hello,

    Haskell 101 question! I discovered that aio_error returns "errno" rather -1. Of course, my aio_error binding is called before my aio_return binding (aio calling sequence "protocol"). I have worked on  Posix OS's for quite a while but am unhappy with non-consistent errno handling ;^(. In any case, I modified my aio_error binding implementation to have a "AIOCB -> IO Errno" signature:

aioError :: AIOCB -> IO Errno
aioError aiocb = do
   allocaBytes (#const sizeof(struct aiocb)) $ \ p_aiocb -> do
      poke p_aiocb aiocb
      errno <- throwErrnoIfMinus1 "aioError" (c_aio_error  p_aiocb)
      return (errno)

foreign import ccall safe "aio.h aio_error"
    c_aio_error :: Ptr AIOCB -> IO Errno

"ghc" thinks that "Errno" should be an instance of "Num":

System/Posix/Aio.hsc:117:15:
    No instance for (Num Errno)
 

Why?

Vasili



On Tue, Jul 1, 2008 at 2:42 AM, Galchin, Vasili <vigalchin@gmail.com> wrote:
Hello,

       I am also testing my aio support. The aio_write binding seems to work ok .. as well as aio_error, Aio_return is a problem child. I think I wrote a really simple binding. I always receive nbytes as 0. I have been staring at the code hoping to catch a stupid mistake. I put putStrLn's in the code. .....Here is the code ...

aioReturn :: AIOCB -> IO (AIOCB, ByteCount)
aioReturn aiocb = do
   allocaBytes (#const sizeof(struct aiocb)) $ \ p_aiocb -> do
      poke p_aiocb aiocb
      count <- throwErrnoIfMinus1 "aioReturn" (c_aio_return  p_aiocb)
      aiocb <- peek p_aiocb
      return (aiocb, fromIntegral count)

foreign import ccall safe "aio.h aio_return"
    c_aio_return :: Ptr AIOCB -> IO CInt

Maybe someone can spot something that I haven't.

Thanks, Vasili