Actual Performance Costs of OOP Objects

[samwgoldman]

Here’s one aspect which hasn’t been mentioned in this thread yet:

Vtables calculated at runtime

I was investigating the poor startup performance of a large OCaml binary that I work with. Once I took care of the egregious cases of expensive code in the module initialization path, I noticed something curious. Through stack sampling, I noticed that my binary’s startup was spending a significant amount of time in the CamlInternalOO module. Specifically, the inherits function. I did some digging, and what I found was quite surprising to me. The vtables for every class is not generated during …

This came up in “the real world” for me, where I help maintain a fairly large binary that had lots of classes linked into it.