Lightweight Concurrency Branch

Simon Peyton Jones simonpj at
Wed Jan 4 10:38:26 UTC 2017


KC never finished work on this stuff.  I’m copying him because I’m sure he’d be happy to help.

KC: can you summarise where you left it?

I think it’s very interesting work, and has the potential to make GHC’s RTS much more malleable, by moving more of it into Haskell libraries instead of deeply-magic C code.

But it’s not easy, because we are reluctant to lose performance, and because there are interactions with STM, weak pointers, foreign function calls, etc.   I think it’d require a bit of commitment to make a go of it.


From: ghc-devs [mailto:ghc-devs-bounces at] On Behalf Of Daniel Bennet
Sent: 28 December 2016 17:23
To: ghc-devs at
Subject: Lightweight Concurrency Branch

The lightweight concurrency branch is highly interesting and relevant to my interests, however, the ghc-lwc2 branch hasn't been updated in several years even though it's listed as an active branch at

The wiki page for the work hasn't been updated in almost two years either,

Relevant papers:
Composable Scheduler Activations for Haskell (2014)<>

Composable Scheduler Activations for Haskell (2016)<>

What remains for integrating this branch into GHC?
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