smp-server: fix service subscription memory leak#1827
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Service subscription counters (totalServiceSubs, serviceSubsCount, ntfServiceSubsCount) are TVar (Int64, IdsHash). modifyTVar' only forces the pair to WHNF, so `n +/- n'` and `idsHash <> idsHash'` stay unevaluated and accumulate an unbounded thunk chain under subscription and delivery churn (the IdsHash chain also retains a bytestring per update) - a space leak proportional to the number of updates. Force both components in addServiceSubs/subtractServiceSubs. Verified with the load bench: svc churn drops from +5.4 KiB/iter (linear) to flat.
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Service subscription counters (totalServiceSubs, serviceSubsCount, ntfServiceSubsCount) are TVar (Int64, IdsHash). modifyTVar' only forces the pair to WHNF, so
n +/- n'andidsHash <> idsHash'stay unevaluated and accumulate an unbounded thunk chain under subscription and delivery churn (the IdsHash chain also retains a bytestring per update) - a space leak proportional to the number of updates.Force both components in addServiceSubs/subtractServiceSubs. Verified with the load bench: svc churn drops from +5.4 KiB/iter (linear) to flat.