[PATCH] Module#name without global constant search
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
Module#name on anonymous modules, there are some other benefits.
- 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.
Behavior changes and caveats:¶
Since we already name module and classes declared with the
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.
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.
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 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.
Eagerly name modules and classes
variable.c: make the hidden ivars
of truth for module and constant names. Assign to them when modules are bind
variable.c: remove references to module name cache, as what used to be the cache
is now the source of truth. Remove rb_class_path_no_cache().
variable.c: remove the hidden ivar
classid. This existed for the purposes of
module name search, which is now replaced. Also, remove the associated
class.c: use rb_set_class_path_string to set the name of Object during boot.
Must use a fstring as this runs before rb_cString is initialized and
creating a normal string leads to a VALUE without a class.
spec/ruby/core/module/name_spec.rb: add a few specs to specify what happens
to Module#name across multiple operations. These specs pass without other
code changes in this commit.
- variable.c (build_const_pathname): build constant path from name as a string. [Feature #15765]