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rrnewton / haskell-lockfree

A collection of different packages for CAS based data structures.
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No more load_load_barrier in GHC HEAD #88

Closed wavewave closed 4 months ago

wavewave commented 10 months ago

therefore, atomic-primops should be changed correspondingly.

https://gitlab.haskell.org/ghc/ghc/-/commits/master/rts/include/stg/SMP.h?ref_type=heads

https://gitlab.haskell.org/ghc/ghc/-/commit/7a7d326cdd5b640c3d40266b88f66b2a2dfeccbe

and store_load_barrier and write_barrier are also removed.

RyanGlScott commented 10 months ago

For context, https://gitlab.haskell.org/ghc/ghc/-/merge_requests/10628 removed these RTS functions.

What is the recommended alternative to using these functions?

bgamari commented 9 months ago

In general we have been trying to move away from explicit barriers entirely. {ACQUIRE,RELEASE,SEQ_CST}_FENCE exist if you really need a barrier but I would strongly recommend using a ordered atomic operation instead (e.g. ACQUIRE_LOAD, RELEASE_STORE, or similar).

RyanGlScott commented 9 months ago

For even further context, https://github.com/rrnewton/haskell-lockfree/commit/4f259b5072a0b1d9701139a1221cca4e7eeef975 is the commit that introduced the use of explicit memory barriers in atomic-primops. Judging from this, it appears that the main consumer is chaselev-deque. If push came to shove, we could just remove the memory barriers from atomic-primops. It would break chaselev-deque, but chaselev-deque is already broken.

RyanGlScott commented 9 months ago

Fixed in #89. I've uploaded these changes to Hackage as atomic-primops-0.8.5.

bgamari commented 7 months ago

It turns out that this fix wasn't quite right as the foreign imports were marked as ccall whereas they should have been prim, leading to https://gitlab.haskell.org/ghc/ghc/-/issues/24595. I will fix.

RyanGlScott commented 7 months ago

@bgamari addressed the issue in https://github.com/rrnewton/haskell-lockfree/issues/88#issuecomment-2021769236 as part of #90. I've released these changes to Hackage as part of atomic-primops-0.8.6.

hsyl20 commented 4 months ago

There is still an issue with these primops. See: https://gitlab.haskell.org/ghc/ghc/-/issues/25010

RyanGlScott commented 4 months ago

Reopening in light of https://gitlab.haskell.org/ghc/ghc/-/issues/25010.

hsyl20 commented 4 months ago

PR: https://github.com/rrnewton/haskell-lockfree/pull/91

RyanGlScott commented 4 months ago

I've uploaded atomic-primops-0.8.8 to Hackage, which contains the changes from #91. Thanks for the patch!