Patrick Perry wrote:
I have the following code:
IOVector n e = IOVector !ConjEnum !Int (ForeignPtr e)! (Ptr e)! Int! newtype Vector n e = IOVector n e
unsafeAtVector :: Vector n e -> Int -> e unsafeAtVector (Vector (IOVector c _ f p inc)) i = let g = if c == Conj then conjugate else id in inlinePerformIO $ do e <- peekElemOff p (i*inc) io <- touchForeignPtr f let e' = g e e' `seq` io `seq` return e' {-# INLINE unsafeAtVector #-}
The Ptr, 'p' is derived from the ForeignPtr, 'f'. For some offset, 'o', it is defined as:
p = unsafeForeignPtrToPtr f `advancePtr` o
The "touchForeignPtr" is there to keep the garbage collector from deallocating the memory before we have a chance to read 'e'. My question is the following: Is the `seq` on `io` necessary (from a safety standpoint)? Or am I just being paranoid?
You're just being paranoid - touchForeignPtr returns a (), so seqing it is a no-op. Cheers, Simon