diff --git a/lib/mini_racer/shared.rb b/lib/mini_racer/shared.rb
new file mode 100644
index 0000000..fdf8202
--- /dev/null
+++ b/lib/mini_racer/shared.rb
@@ -0,0 +1,380 @@
+# This code used to be shared in lib/mini_racer.rb
+# but was moved to the extension with https://github.com/rubyjs/mini_racer/pull/325.
+# So now this is effectively duplicate logic with C/C++ code.
+# Maybe one day it can be actually shared again between both backends.
+
+module MiniRacer
+
+  MARSHAL_STACKDEPTH_DEFAULT = 2**9-2
+  MARSHAL_STACKDEPTH_MAX_VALUE = 2**10-2
+
+  class FailedV8Conversion
+    attr_reader :info
+    def initialize(info)
+      @info = info
+    end
+  end
+
+  # helper class returned when we have a JavaScript function
+  class JavaScriptFunction
+    def to_s
+      "JavaScript Function"
+    end
+  end
+
+  class Isolate
+    def initialize(snapshot = nil)
+      unless snapshot.nil? || snapshot.is_a?(Snapshot)
+        raise ArgumentError, "snapshot must be a Snapshot object, passed a #{snapshot.inspect}"
+      end
+
+      # defined in the C class
+      init_with_snapshot(snapshot)
+    end
+  end
+
+  class Platform
+    class << self
+      def set_flags!(*args, **kwargs)
+        flags_to_strings([args, kwargs]).each do |flag|
+          # defined in the C class
+          set_flag_as_str!(flag)
+        end
+      end
+
+      private
+
+      def flags_to_strings(flags)
+        flags.flatten.map { |flag| flag_to_string(flag) }.flatten
+      end
+
+      # normalize flags to strings, and adds leading dashes if needed
+      def flag_to_string(flag)
+        if flag.is_a?(Hash)
+          flag.map do |key, value|
+            "#{flag_to_string(key)} #{value}"
+          end
+        else
+          str = flag.to_s
+          str = "--#{str}" unless str.start_with?('--')
+          str
+        end
+      end
+    end
+  end
+
+  # eval is defined in the C class
+  class Context
+
+    class ExternalFunction
+      def initialize(name, callback, parent)
+        unless String === name
+          raise ArgumentError, "parent_object must be a String"
+        end
+        parent_object, _ , @name = name.rpartition(".")
+        @callback = callback
+        @parent = parent
+        @parent_object_eval = nil
+        @parent_object = nil
+
+        unless parent_object.empty?
+          @parent_object = parent_object
+
+          @parent_object_eval = ""
+          prev = ""
+          first = true
+          parent_object.split(".").each do |obj|
+            prev << obj
+            if first
+              @parent_object_eval << "if (typeof #{prev} === 'undefined') { #{prev} = {} };\n"
+            else
+              @parent_object_eval << "#{prev} = #{prev} || {};\n"
+            end
+            prev << "."
+            first = false
+          end
+          @parent_object_eval << "#{parent_object};"
+        end
+        notify_v8
+      end
+    end
+
+    def initialize(max_memory: nil, timeout: nil, isolate: nil, ensure_gc_after_idle: nil, snapshot: nil, marshal_stack_depth: nil)
+      options ||= {}
+
+      check_init_options!(isolate: isolate, snapshot: snapshot, max_memory: max_memory, marshal_stack_depth: marshal_stack_depth, ensure_gc_after_idle: ensure_gc_after_idle, timeout: timeout)
+
+      @functions = {}
+      @timeout = nil
+      @max_memory = nil
+      @current_exception = nil
+      @timeout = timeout
+      @max_memory = max_memory
+      @marshal_stack_depth = marshal_stack_depth
+
+      # false signals it should be fetched if requested
+      @isolate = isolate || false
+
+      @ensure_gc_after_idle = ensure_gc_after_idle
+
+      if @ensure_gc_after_idle
+        @last_eval = nil
+        @ensure_gc_thread = nil
+        @ensure_gc_mutex = Mutex.new
+      end
+
+      @disposed = false
+
+      @callback_mutex = Mutex.new
+      @callback_running = false
+      @thread_raise_called = false
+      @eval_thread = nil
+
+      # defined in the C class
+      init_unsafe(isolate, snapshot)
+    end
+
+    def isolate
+      return @isolate if @isolate != false
+      # defined in the C class
+      @isolate = create_isolate_value
+    end
+
+    def eval(str, options=nil)
+      raise(ContextDisposedError, 'attempted to call eval on a disposed context!') if @disposed
+
+      filename = options && options[:filename].to_s
+
+      @eval_thread = Thread.current
+      isolate_mutex.synchronize do
+        @current_exception = nil
+        timeout do
+          eval_unsafe(str, filename)
+        end
+      end
+    ensure
+      @eval_thread = nil
+      ensure_gc_thread if @ensure_gc_after_idle
+    end
+
+    def call(function_name, *arguments)
+      raise(ContextDisposedError, 'attempted to call function on a disposed context!') if @disposed
+
+      @eval_thread = Thread.current
+      isolate_mutex.synchronize do
+        timeout do
+          call_unsafe(function_name, *arguments)
+        end
+      end
+    ensure
+      @eval_thread = nil
+      ensure_gc_thread if @ensure_gc_after_idle
+    end
+
+    def dispose
+      return if @disposed
+      isolate_mutex.synchronize do
+        return if @disposed
+        dispose_unsafe
+        @disposed = true
+        @isolate = nil # allow it to be garbage collected, if set
+      end
+    end
+
+
+    def attach(name, callback)
+      raise(ContextDisposedError, 'attempted to call function on a disposed context!') if @disposed
+
+      wrapped = lambda do |*args|
+        begin
+
+          r = nil
+
+          begin
+            @callback_mutex.synchronize{
+              @callback_running = true
+            }
+            r = callback.call(*args)
+          ensure
+            @callback_mutex.synchronize{
+              @callback_running = false
+            }
+          end
+
+          # wait up to 2 seconds for this to be interrupted
+          # will very rarely be called cause #raise is called
+          # in another mutex
+          @callback_mutex.synchronize {
+            if @thread_raise_called
+              sleep 2
+            end
+          }
+
+          r
+
+        ensure
+          @callback_mutex.synchronize {
+            @thread_raise_called = false
+          }
+        end
+      end
+
+      isolate_mutex.synchronize do
+        external = ExternalFunction.new(name, wrapped, self)
+        @functions["#{name}"] = external
+      end
+    end
+
+    private
+
+    def ensure_gc_thread
+      @last_eval = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+      @ensure_gc_mutex.synchronize do
+        @ensure_gc_thread = nil if !@ensure_gc_thread&.alive?
+        return if !Thread.main.alive? # avoid "can't alloc thread" exception
+        @ensure_gc_thread ||= Thread.new do
+          ensure_gc_after_idle_seconds = @ensure_gc_after_idle / 1000.0
+          done = false
+          while !done
+            now = Process.clock_gettime(Process::CLOCK_MONOTONIC)
+
+            if @disposed
+              @ensure_gc_thread = nil
+              break
+            end
+
+            if !@eval_thread && ensure_gc_after_idle_seconds < now - @last_eval
+              @ensure_gc_mutex.synchronize do
+                isolate_mutex.synchronize do
+                  if !@eval_thread
+                    isolate.low_memory_notification if !@disposed
+                    @ensure_gc_thread = nil
+                    done = true
+                  end
+                end
+              end
+            end
+            sleep ensure_gc_after_idle_seconds if !done
+          end
+        end
+      end
+    end
+
+    def stop_attached
+      @callback_mutex.synchronize{
+        if @callback_running
+          @eval_thread.raise ScriptTerminatedError, "Terminated during callback"
+          @thread_raise_called = true
+        end
+      }
+    end
+
+    def timeout(&blk)
+      return blk.call unless @timeout
+
+      mutex = Mutex.new
+      done = false
+
+      rp,wp = IO.pipe
+
+      t = Thread.new do
+        begin
+          result = rp.wait_readable(@timeout/1000.0)
+          if !result
+            mutex.synchronize do
+              stop unless done
+            end
+          end
+        rescue => e
+          STDERR.puts e
+          STDERR.puts "FAILED TO TERMINATE DUE TO TIMEOUT"
+        end
+      end
+
+      rval = blk.call
+      mutex.synchronize do
+        done = true
+      end
+
+      wp.close
+
+      # ensure we do not leak a thread in state
+      t.join
+      t = nil
+
+      rval
+    ensure
+      # exceptions need to be handled
+      wp&.close
+      t&.join
+      rp&.close
+    end
+
+    def check_init_options!(isolate:, snapshot:, max_memory:, marshal_stack_depth:, ensure_gc_after_idle:, timeout:)
+      assert_option_is_nil_or_a('isolate', isolate, Isolate)
+      assert_option_is_nil_or_a('snapshot', snapshot, Snapshot)
+
+      assert_numeric_or_nil('max_memory', max_memory, min_value: 10_000, max_value: 2**32-1)
+      assert_numeric_or_nil('marshal_stack_depth', marshal_stack_depth, min_value: 1, max_value: MARSHAL_STACKDEPTH_MAX_VALUE)
+      assert_numeric_or_nil('ensure_gc_after_idle', ensure_gc_after_idle, min_value: 1)
+      assert_numeric_or_nil('timeout', timeout, min_value: 1)
+
+      if isolate && snapshot
+        raise ArgumentError, 'can only pass one of isolate and snapshot options'
+      end
+    end
+
+    def assert_numeric_or_nil(option_name, object, min_value:, max_value: nil)
+      if max_value && object.is_a?(Numeric) && object > max_value
+        raise ArgumentError, "#{option_name} must be less than or equal to #{max_value}"
+      end
+
+      if object.is_a?(Numeric) && object < min_value
+        raise ArgumentError, "#{option_name} must be larger than or equal to #{min_value}"
+      end
+
+      if !object.nil? && !object.is_a?(Numeric)
+        raise ArgumentError, "#{option_name} must be a number, passed a #{object.inspect}"
+      end
+    end
+
+    def assert_option_is_nil_or_a(option_name, object, klass)
+      unless object.nil? || object.is_a?(klass)
+        raise ArgumentError, "#{option_name} must be a #{klass} object, passed a #{object.inspect}"
+      end
+    end
+  end
+
+  # `size` and `warmup!` public methods are defined in the C class
+  class Snapshot
+    def initialize(str = '')
+      # ensure it first can load
+      begin
+        ctx = MiniRacer::Context.new
+        ctx.eval(str)
+      rescue MiniRacer::RuntimeError => e
+        raise MiniRacer::SnapshotError.new, e.message, e.backtrace
+      end
+
+      @source = str
+
+      # defined in the C class
+      load(str)
+    end
+
+    def warmup!(src)
+      # we have to do something here
+      # we are bloating memory a bit but it is more correct
+      # than hitting an exception when attempty to compile invalid source
+      begin
+        ctx = MiniRacer::Context.new
+        ctx.eval(@source)
+        ctx.eval(src)
+      rescue MiniRacer::RuntimeError => e
+        raise MiniRacer::SnapshotError.new, e.message, e.backtrace
+      end
+
+      warmup_unsafe!(src)
+    end
+  end
+end
diff --git a/lib/mini_racer/truffleruby.rb b/lib/mini_racer/truffleruby.rb
index ff31b45..c4eac0e 100644
--- a/lib/mini_racer/truffleruby.rb
+++ b/lib/mini_racer/truffleruby.rb
@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require_relative 'shared'
+
 module MiniRacer
 
   class Context