Wait only on read Vars

[anacrolix]

I noticed that Tx.verify waits on a global condition. Have you considered installing some synchronisation primitive on to each Var that's read for a Tx, and when committing a write, signalling all waiters on only those Vars that are written? I imagine the overhead may be a larger for toy examples, but it might be possible to minimize overhead by lazily creating and reusing the primitive when Txs have to wait, and using and reusing slices for the waiters on the Vars (they're quite efficient). There's currently no benchmark that would demonstrate any speed-up for a change like this if it's plausible.

[lukechampine]

To be honest, I consider this package to be mostly "for fun" and not intended for serious use. It hasn't been touched in many years at this point. If you're interested in developing it further, I'll happily post a deprecation notice and link to your fork. Regardless, I suppose I should put some sort of disclaimer in the README.

[anacrolix]

I have implemented this here: anacrolix/stm@master...anacrolix:var-conds. I also have restructured the code, and added some tests here: https://github.com/anacrolix/stm.

[anacrolix]

@lukechampine I have started developing this further. I've created some integrations with context, a set of persistent data structures, transaction return values, and a rate limiter to supplement the core. If you'd like to deprecate in favour of my implementation I think it might be appropriate now. Let me know your thoughts.

[lukechampine]

Cool -- passing the torch to you now :)