I want to note something, which is that if we did link in cas/store_load_barrier, then your lockfree queue would always be synchronized, even if you didn't compile with -threaded. Perhaps this is not a big deal, but it is generally nice to not pay the cost of synchronization when it is unnecessary. So it would be better if there were threaded/nonthreaded variants which you could use instead. How does that sound? (Fortunately, you are not inlining the functions, so it's totally possible for this to happen. We'd have a tougher row to hoe if you needed to inline these functions.) Edward Excerpts from Ryan Newton's message of Thu Jul 18 06:17:44 -0700 2013:
The "atomic-primops" library depends on symbols such as store_load_barrier and "cas", which are defined in SMP.h. Thus the result is that if the program is linked WITHOUT "-threaded", the user gets a linker error about undefined symbols.
The specific place it's used is in the 'foreign "C"' bits of this .cmm code:
https://github.com/rrnewton/haskell-lockfree-queue/blob/87e63b21b2a6c375e93c...
I'm trying to explore hacks that will enable me to pull in those functions during compile time, without duplicating a whole bunch of code from the RTS. But it's a fragile business.
It seems to me that some of these routines have general utility. In future versions of GHC, could we consider linking in those routines irrespective of "-threaded"?
-Ryan