I was looking at the eventlog code, and I wanted to move processing of a full eventlog buffer into Haskell, instead of the now fixed behavior of writing the data to a file. To do this, I though that having a haskell process blocked on an MVar, or Chan would be nice, and then some way to signal the process. But the low-level PrimOps for MVars, takeMVar, tryTakeMVar etc are in PrimOps.cmm and I don't know how to call them from the RTS. This lead me to question what the point of out-of-line PrimOps in PrimOps.cmm is. I don't think the commentary covers this. http://hackage.haskell.org/trac/ghc/wiki/Commentary/PrimOps So why aren't all the stuff in PrimOps.cmm just "ccall" wrappers around C implementations? Wouldn't that in general be more flexible for the RTS? Alexander