Reuse parsed expression in SpelValueExpressionResolver

[doumdoum]

So far expression is parsed everytime the value is resolved.
My proposal is to reuse the parsed expression.
Since the value resolver is used only for a predefined set of expressions the map should contain only a few items.

[wilkinsona]

Since the value resolver is used only for a predefined set of expressions

I don't think we can be certain of that as the ValueExpressionResolver is exposed as a bean. It could then be (mis)used in such a way that the cache becomes very large. Using Spring Framework's ConcurrentReferenceHashMap would avoid this potential problem.

So far expression is parsed everytime the value is resolved. My proposal is to reuse the parsed expression.

I wonder if this may be premature optimisation as we haven't seen any issues with @SpanTag where the SpEL-based resolver's been used for some time now. Do you have performance data showing the expression resolution adding an unacceptably large overhead?

[doumdoum]

@wilkinsona, i did some rudimentary performance tests and the gain is marginal (few micro-seconds).
Maybe not worth it.

[wilkinsona]

It's certainly not clear that it's worth it. Let's leave things as they are for now. We can reconsider in the future if it becomes apparent that we need to strike a different balance between memory usage and CPU usage. Thanks anyway.