Correctly reset new TVar values when restoring snapshots #332
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This adds the overhead of constructing the effect to every STM transaction, which I worried would be a large cost; but it turns out that the overhead is negligible.
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Summary
Previously, the setup action for an STM transaction was just the transaction itself. This works fine for replacing
SWrites, but not forSNews, as it just creates a new new TVar and doesn't reset the value of the existing one.This PR records an explicit "effect" of STM transactions to be used in snapshots, in the same way as non-STM effects are replayed when running a snapshot.
This adds the overhead of constructing the effect to every STM transaction, which I worried would be a large cost; but it turns out that the overhead is negligible.
Related issues: fixes #331