Michael Weber wrote:
> It seems, today's GHC made the problem disappear (or, at least, it
> disappeared between 1999/12/06 and 2000/01/09), my test case now
> works as expected...
>
> Sven, what about yours? [...]
*Sigh* A similar problem just occurred again! Given the following
code snippet from the FFI proposal:
-----------------------------------------------------
outParamWith :: (a -> Int) -> (Addr -> IO a) -> (Addr -> IO b) -> IO (b,a)
outParamWith sizeOf_ unmarshal_ act = do
buf <- malloc (sizeOf_ undefined)
retVal <- act buf
val <- unmarshal_ buf
free buf -- ************** everything works if we comment out this free
return (retVal, val)
-----------------------------------------------------
It seems as if the unmarshaling (`unmarshal_ buf') is done at the
moment the value of `val' is needed, which depends on the caller of
outParamWith. But at this moment `free buf' has already happend and
Electric Fence correctly complains.
Further investigation shows that this happens when `unmarshal_' is
bound to something like
fixIO (\val -> <real unmarshaling via readCharOffAddr is done here>)
Hmmm, is this not as strict as I thought? %-( Perhaps I should
try `seq' on the returned value...
Confused as usual,
Sven
--
Sven Panne Tel.: +49/89/2178-2235
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