The Curious Case of the Bad Clone

on YouTube ↗52m

" summary

A two-line Sorbet sig triggers a 150% slowdown by causing about 1,600 method_added calls during cloning. Investigation uses CPU profiles, bundle open edits, puts and binding.pry, rails runner, and object space TraceObjectAllocations to find an unnamed singleton-class clone path. A minimal reproducer and Rails bug-template script isolates the issue, a PR with Alan Wu changes the clone/attach guard, and the fix lands in Ruby 3.0 (and is backported to 2.7).

AI-written summary · about

" chapters (12)

1. 0:00Introduction
2. 1:43What is Sorbet
3. 3:11Runtime magic with method_added
4. 7:27Performance regression
5. 11:28Mystery of cloned methods
6. 14:02Kernel.clone and Singleton behavior
7. 20:47Root cause in Rails sharding
8. 27:37after_find and object cloning
9. 33:15Reproducing the bug
10. 41:41Singleton class cloning
11. 46:24Fixing Singleton class cloning
12. 50:21Verifying fix in Ruby 3

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