Feature #15765
Updated by alanwu (Alan Wu) over 5 years ago
Hello! The current implementation of `Module#name` is known for having sub-optimal performance when it comes to anonymous modules. (see #11119 and #15625) I have put together a reimplementation of `Module#name`, which works by eagerly naming modules and classes when they are assigned to constants. Besides solving the performance issues for `Module#name` on anonymous modules, there are some other benefits. This patch: - removes more code than it adds - makes normal class and module definition slightly faster (definitions like `class Foo; end`) - slightly reduces memory usage for classes and modules due to the removal of a hidden ivar - improves the performance of defining modules and classes under an anonymous module. This used to execute a global search each time. search. ### Behavior changes and caveats: Since we already name module and classes declared with the `class` and `module` keyword on trunk, this patch mostly targets anonymous modules. I tried my best keeping the behaviors consistent with the current implementation, but there are some small behavioral changes. ```ruby mod = Module.new mod::BeforeToS = Module.new mod.const_set(:BeforeToS2, Module.new) mod.to_s # on trunk, the VM starts naming modules assigned under mod after calling to_s mod::AfterToS = Module.new mod.const_set(:AfterToS2, Module.new) p mod::BeforeToS.name # nil on both p mod::BeforeToS2.name # nil on both p mod::AfterToS.name # "#<Module:0x0000563494b1cca8>::AfterToS" on trunk, nil after patch p mod::AfterToS2.name # "#<Module:0x0000563494b1cca8>::AfterToS2" on trunk, nil after patch ``` This prints 4 nils after my patch, as I think the behavior on trunk is unintentional. A few C APIs also have the same effect as calling to_s. They are all changed to be side-effect free. ```ruby m = Module.new m::Child = Module.new Mod = m p Object.send(:remove_const, :Mod)::Child.name ``` This prints nil on trunk and `Mod::Child` under this patch. `rb_name_class` is removed, as it does nothing in this new implementation. Not sure if this is public API. Since the recursive naming is done with a recursive function, when function. When a deeply nested anonymous module is assigned to a constant, it is technically possible for this implementation to throw a `StackError`. I had a version which does heap allocation to deal with this, but I picked this version for performance in the common cases. Anonymous modules are rare as is, and one would have to build a structure nested thousands level deep for this to happen. On my system it can name a module fifty thousand levels deep without problem. I think these changes are fairly minimal and acceptable.