Use Map::computeIfAbsent where feasible

[quaff]

No description provided.

[jhoeller]

We had some performance regressions in the past with the use of computeIfAbsent, so let's be rather careful there. There's also the overhead of the lambda instance but primarily it's the stronger locking of computeIfAbsent as opposed to separate get and put steps.

[quaff]

We had some performance regressions in the past with the use of computeIfAbsent, so let's be rather careful there. There's also the overhead of the lambda instance but primarily it's the stronger locking of computeIfAbsent as opposed to separate get and put steps.

I didn't aware of that, could someone helps to identify which parts should be reverted, or should I close this PR?

[bclozel]

All calls to concurrent collections and ad hoc caches. Which is most of what this PR is.
The rest is mostly cosmetic changes and is not adding much.