Feature #15765

[PATCH] Module#name without global constant search

Added by alanwu (Alan Wu) 6 months ago. Updated 5 months ago.

Target version:



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.

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.

mod =
mod::BeforeToS =

mod.to_s # on trunk, the VM starts naming modules assigned under mod after calling to_s

mod::AfterToS =

p  # nil on both
p # nil on both 
p   # "#<Module:0x0000563494b1cca8>::AfterToS" on trunk, nil after patch
p  # "#<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 =
m::Child =
Mod = m
p Object.send(:remove_const, :Mod)

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.


benchmarks.rb (3.16 KB) benchmarks.rb alanwu (Alan Wu), 04/12/2019 04:09 AM
0001-Eagerly-name-modules-and-classes.patch (19.8 KB) 0001-Eagerly-name-modules-and-classes.patch alanwu (Alan Wu), 04/12/2019 04:09 AM

Related issues

Related to Ruby master - Bug #15891: FrozenError when assigning frozen class to constantClosedActions

Associated revisions

Revision b00f280d
Added by alanwu (Alan Wu) 5 months ago

Eagerly name modules and classes

  • variable.c: make the hidden ivars classpath and tmp_classpath the source
    of truth for module and constant names. Assign to them when modules are bind
    to constants.

  • 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.

[Feature #15765]

Revision 1b20d6a6
Added by alanwu (Alan Wu) 5 months ago

Extract build_const_pathname

  • variable.c (build_const_pathname): build constant path from name as a string. [Feature #15765]

Revision 48f3dc3c
Added by nobu (Nobuyoshi Nakada) 5 months ago

Set namespace tree

  • variable.c (set_namespace_path): set path to the whole namespace tree. [Feature #15765]


Updated by alanwu (Alan Wu) 6 months ago

This is for #11119 and #15625.


Updated by alanwu (Alan Wu) 6 months ago

  • Description updated (diff)

Updated by nobu (Nobuyoshi Nakada) 5 months ago

  • Status changed from Open to Closed

Closed by b00f280d4b


Updated by nobu (Nobuyoshi Nakada) 5 months ago

  • Related to Bug #15891: FrozenError when assigning frozen class to constant added

Also available in: Atom PDF