Ruby Box - Ruby’s in-process separation of Classes and Modules ↑

Ruby Box is designed to provide separated spaces in a Ruby process, to isolate applications and libraries.

Known issues ↑

TODOs ↑

How to use ↑

Enabling Ruby Box ↑

First, an environment variable should be set at the ruby process bootup: RUBY_BOX=1. The only valid value is 1 to enable namespace. Other values (or unset RUBY_BOX) means disabling namespace. And setting the value after Ruby program starts doesn’t work.

Using Ruby Box ↑

Ruby::Box class is the entrypoint of Ruby Box.

box = Ruby::Box.new
box.require('something') # or require_relative, load

The required file (either .rb or .so/.dll/.bundle) is loaded in the box (box here). The required/loaded files from something will be loaded in the box recursively.

# something.rb

X = 1

class Something
  def self.x = X
  def x = ::X
end

Classes/modules, those methods and constants defined in the box can be accessed via ns object.

p ns::Something.x  # 1

X = 2
p X                # 2
p ::X              # 2
p box::Something.x  # 1
p box::X            # 1

Instance methods defined in the box also run with definitions in the box.

s = box::Something.new

p s.x  # 1

Specifications ↑

Ruby Box types ↑

There are two box types:

There is the root box, just a single box in a Ruby process. Ruby bootstrap runs in the root box, and all builtin classes/modules are defined in the root box. (See “Builtin classes and modules”.)

User boxes are to run user-written programs and libraries loaded from user programs. The user’s main program (specified by the ruby command line argument) is executed in the “main” box, which is a user namespace automatically created at the end of Ruby’s bootstrap, copied from the root box.

When Ruby::Box.new is called, an “optional” box (a user, non-main box) is created, copied from the root box. All user boxes are flat, copied from the root box.

Ruby Box class and instances ↑

Ruby::Box is a class, as a subclass of Module. Ruby::Box instances are a kind of Module.

Classes and modules defined in boxes ↑

The classes and modules, newly defined in a box box, are accessible via box. For example, if a class A is defined in box, it is accessible as box::A from outside of the box.

In the box box, A can be referred to as A (and ::A).

Built-in classes and modules reopened in boxes ↑

In boxes, builtin classes/modules are visible and can be reopened. Those classes/modules can be reopened using class or module clauses, and class/module definitions can be changed.

The changed definitions are visible only in the box. In other boxes, builtin classes/modules and those instances work without changed definitions.

# in foo.rb
class String
  BLANK_PATTERN = /\A\s*\z/
  def blank?
    self =~ BLANK_PATTERN
  end
end

module Foo
  def self.foo = "foo"

  def self.foo_is_blank?
    foo.blank?
  end
end

Foo.foo.blank? #=> false
"foo".blank?   #=> false

# in main.rb
box = Ruby::Box.new
box.require('foo')

box::Foo.foo_is_blank? #=> false   (#blank? called in box)

"foo".blank?          # NoMethodError
String::BLANK_PATTERN # NameError

The main box and box are different boxes, so monkey patches in main are also invisible in box.

Builtin classes and modules ↑

In the box context, “builtin” classes and modules are classes and modules:

Hereafter, “builtin classes and modules” will be referred to as just “builtin classes”.

Builtin classes referred via box objects ↑

Builtin classes in a box box can be referred from other boxes. For example, box::String is a valid reference, and String and box::String are identical (String == box::String, String.object_id == box::String.object_id).

box::String-like reference returns just a String in the current box, so its definition is String in the box, not in box.

# foo.rb
class String
  def self.foo = "foo"
end

# main.rb
box = Ruby::Box.new
box.require('foo')

box::String.foo  # NoMethodError

Class instance variables, class variables, constants ↑

Builtin classes can have different sets of class instance variables, class variables and constants between boxes.

# foo.rb
class Array
  @v = "foo"
  @@v = "_foo_"
  V = "FOO"
end

Array.instance_variable_get(:@v) #=> "foo"
Array.class_variable_get(:@@v)   #=> "_foo_"
Array.const_get(:V)              #=> "FOO"

# main.rb
box = Ruby::Box.new
box.require('foo')

Array.instance_variable_get(:@v) #=> nil
Array.class_variable_get(:@@v)   # NameError
Array.const_get(:V)              # NameError

Global variables ↑

In boxes, changes on global variables are also isolated in the boxes. Changes on global variables in a box are visible/applied only in the box.

# foo.rb
$foo = "foo"
$VERBOSE = nil

puts "This appears: '#{$foo}'"

# main.rb
p $foo      #=> nil
p $VERBOSE  #=> false

box = Ruby::Box.new
box.require('foo')  # "This appears: 'foo'"

p $foo      #=> nil
p $VERBOSE  #=> false

Top level constants ↑

Usually, top level constants are defined as constants of Object. In boxes, top level constants are constants of Object in the box. And the box object box‘s constants are strictly equal to constants of Object.

# foo.rb
FOO = 100

FOO         #=> 100
Object::FOO #=> 100

# main.rb
box = Ruby::Box.new
box.require('foo')

box::FOO      #=> 100

FOO          # NameError
Object::FOO  # NameError

Top level methods ↑

Top level methods are private instance methods of Object, in each box.

# foo.rb
def yay = "foo"

class Foo
  def self.say = yay
end

Foo.say #=> "foo"
yay     #=> "foo"

# main.rb
box = Ruby::Box.new
box.require('foo')

box.Foo.say  #=> "foo"

yay  # NoMethodError

There is no way to expose top level methods in boxes to others. (See “Expose top level methods as a method of the box object” in “Discussions” section below)

Ruby Box scopes ↑

Ruby Box works in file scope. One .rb file runs in a single box.

Once a file is loaded in a box box, all methods/procs defined/created in the file run in box.

Implementation details ↑

ISeq inline method/constant cache ↑

As described above in “Ruby Box scopes”, an “.rb” file runs in a box. So method/constant resolution will be done in a box consistently.

That means ISeq inline caches work well even with boxes. Otherwise, it’s a bug.

Method call global cache (gccct) ↑

rb_funcall() C function refers to the global cc cache table (gccct), and the cache key is calculated with the current box.

So, rb_funcall() calls have a performance penalty when Ruby Box is enabled.

Current box and loading box ↑

The current box is the box that the executing code is in. Ruby::Box.current returns the current box object.

The loading box is an internally managed box to determine the box to load newly required/loaded files. For example, box is the loading box when box.require("foo") is called.

Discussions ↑

More builtin methods written in Ruby ↑

If Ruby Box is enabled by default, builtin methods can be written in Ruby because it can’t be overridden by users’ monkey patches. Builtin Ruby methods can be JIT-ed, and it could bring performance reward.

Monkey patching methods called by builtin methods ↑

Builtin methods sometimes call other builtin methods. For example, Hash#map calls Hash#each to retrieve entries to be mapped. Without Ruby Box, Ruby users can overwrite Hash#each and expect the behavior change of Hash#map as a result.

But with boxes, Hash#map runs in the root box. Ruby users can define Hash#each only in user boxes, so users cannot change Hash#map‘s behavior in this case. To achieve it, users should override bothHash#map and Hash#each (or only Hash#map).

It is a breaking change.

Users can define methods using Ruby::Box.root.eval(...), but it’s clearly not ideal API.

Context of $LOAD_PATH and $LOADED_FEATURES ↑

Global variables $LOAD_PATH and $LOADED_FEATURES control require method behaviors. So those variables are determined by the loading box instead of the current box.

This could potentially conflict with the user’s expectations. We should find the solution.

Expose top level methods as a method of the box object ↑

Currently, top level methods in boxes are not accessible from outside of the box. But there might be a use case to call other box’s top level methods.

Split root and builtin box ↑

Currently, the single “root” box is the source of classext CoW. And also, the “root” box can load additional files after starting main script evaluation by calling methods which contain lines like require "openssl".

That means, user boxes can have different sets of definitions according to when it is created.

[root]
 |
 |----[main]
 |
 |(require "openssl" called in root)
 |
 |----[box1] having OpenSSL
 |
 |(remove_const called for OpenSSL in root)
 |
 |----[box2] without OpenSSL

This could cause unexpected behavior differences between user boxes. It should NOT be a problem because user scripts which refer to OpenSSL should call require "openssl" by themselves. But in the worst case, a script (without require "openssl") runs well in box1, but doesn’t run in box2. This situation looks like a “random failure” to users.

An option possible to prevent this situation is to have “root” and “builtin” boxes.

This design realizes a consistent source of box CoW.

Separate cc_tbl and callable_m_tbl, cvc_tbl for less classext CoW ↑

The fields of rb_classext_t contains several cache(-like) data, cc_tbl(callcache table), callable_m_tbl(table of resolved complemented methods) and cvc_tbl(class variable cache table).

The classext CoW is triggered when the contents of rb_classext_t are changed, including cc_tbl, callable_m_tbl, and cvc_tbl. But those three tables are changed by just calling methods or referring class variables. So, currently, classext CoW is triggered much more times than the original expectation.

If we can move those three tables outside of rb_classext_t, the number of copied rb_classext_t will be much less than the current implementation.