Skip lambda allocation in FindTransientAnnotation

[joaocpaiva]

Issues

Total allocation of this method is at 3.09%:

• 1% for delegate
• 1.61% for enumerator
• 0.48% for closure.

Description

This change replaces the usage of Linq in this method, with manual implementation, avoiding lambda allocation. Every time we invoke Any, it allocates a lambda. This is normally meaningless, when not present in the hot path. Since this is present in AGS hot path, it is costing 1% of allocations just in this lambda. This is a lot.

Also removes the usage of enumerator, replacing with O(1) random access for loop. The ArrayVersioningList is better for search scenarios because we can save the enumerator allocation all together, and use O(1) random access. The LinkedVersioningList would only be useful if this data structure is changing very often at runtime, which I don't think is the case? Main scenario will be search at runtime? So I am proposing to replace with ArrayVersioningList. Furthermore, when adding a new element, it was swapping to ArrayVersioningList if there were 5 or more elements, hence I don't really see the benefit of not using ArrayVersioningList for all cases, particular if the search scenario is the main path.

Not using Linq.Any(), is not only good for memory but also for CPU as we can see in this benchmark:

Checklist (Uncheck if it is not completed)

• Test cases added
• Build and test with one-click build and test script passed

[gathogojr]

LG

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Total files changed: 4

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[habbes]

If I understand the implementation, this results in a new array being allocated, and elements copied from the previous array to the new one. Doesn't this lead to a larger memory footprint and more GC over time? Is the rationale that we're willing to sacrifice memory in order to get faster search times?