Use stm-containers to avoid contention in Vector #79
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This PR switches the
Vectormetric away fromIORef (Map k v)to StmContainers.Map k v`, significantly improving performance in concurrent modification.This is a breaking change with very slight impact: the constraint
Hashableis added to two functiosn which previously got by on mereLabel. SinceLabelappears to mostly be useful for tuples of texts, this should not break most use sites.I created benchmarks on my other fork with other memory improvements: parsonsmatt#1
stm-containersis faster with two threads and up; with high contention and lots of concurrent modification (as we expect to see in a webserver),stm-containerslevels out whileIORef (Map k v)runs into massive concurrency contention.In the other PR, I left the old implementation, and switched the default. In this PR I've simply used the faster implementation. I don't think the meager performance benefit in single threaded applications is worth complicating the code in library.
This is also a fix to #75