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

Jonathan Cast jonathanccast at fastmail.fm
Wed Jul 2 02:15:34 EDT 2008

On Wed, 2008-07-02 at 02:07 -0400, Brandon S. Allbery KF8NH wrote:
> On 2008 Jul 2, at 1:42, Galchin, Vasili wrote:
> >       errno <- throwErrnoIfMinus1 "aioError" (c_aio_error  p_aiocb)
> > 
> > "ghc" thinks that "Errno" should be an instance of "Num":
> > 
> > System/Posix/Aio.hsc:117:15:
> >     No instance for (Num Errno)
> I expect so it can compare it to -1(throwErrnoIfMinusOne).  But if the
> return value is actually an errno and not -1 to indicate error (which
> it is if I read the manpage correctly), you don't want
> throwErrnoIfMinus1 anyway; I suspect you want to wrap the return value
> of c_aio_return (which should be IO CInt) in an Errno constructor,
> then use errnoToIOError if you really want to raise an IOError.
> (What were you expecting for "count"?  I see none, just an errno.)
> Note that it *never* returns -1; it returns 0 for successful
> completion for the aiocb, EINPROGRESS if it's still working, and the
> appropriate errno if it failed.

It seems as though it can return -1 if given non-sensical input.  But in
that case, the nicely type-correct thing to do would still be to have
the C binding return a CInt, and wrap that after the call to
throwErrnoIfMinus1 (in this case, `errno' still refers to the global
errno, set to EINVAL).


More information about the Haskell-Cafe mailing list