On 10/01/2012 17:19, Ryan Newton wrote:

Hello there,

I was wondering what the recommendations would be for getting CAS on [mutable] vector elements?

I thought that as a first step I might create an a library that does the trick only for unboxed vectors, by using bits-atomic (i.e. FFI + GCC intrinsics).

Roman Leshchinskiy recommended against depending on GCC. He thought, therefore, that not only boxed arrays but unboxed ones would need an extra PrimOp to be handled properly:

...

You can't rely on gcc extensions because code is usually compiled with the native code generator nowadays and doesn't go through gcc. The dependency on gcc will (hopefully) be dropped eventually anyway. So you'd probably also want primops for unboxed arrrays and Addr#.

Any advice?

For boxed arrays you need a PrimOp of course (like catMutVar#). For unboxed arrays you could get away with FFI, but a PrimOp would be better because it could be inline. But to get it inline would mean modifying the native and LLVM backends to support CAS operations. If I were you I would use FFI for now. The cost of the out-of-line call is much less than the cost of the CAS anyway. A gcc dependency is not a big deal, it's available on all Unix-like platforms and I don't see us removing it from the Windows installs any time soon. Cheers, Simon