[Haskell-cafe] Re: POSIX AIO (asych I/O) ...

[Galchin, Vasili]

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 at 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
>
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