Replace use of _id2ref in DRb.

lib/drb/drb.rb

@@ -48,6 +48,7 @@
 
 require 'socket'
 require 'io/wait'
+require 'weakref'
 require_relative 'eq'
 
 #
@@ -355,30 +356,68 @@ class DRbConnError < DRbError; end
 
   # Class responsible for converting between an object and its id.
   #
-  # This, the default implementation, uses an object's local ObjectSpace
+  # This, the default implementation, uses an object's runtime-assigned
   # __id__ as its id.  This means that an object's identification over
   # drb remains valid only while that object instance remains alive
   # within the server runtime.
   #
   # For alternative mechanisms, see DRb::TimerIdConv in drb/timeridconv.rb
   # and DRbNameIdConv in sample/name.rb in the full drb distribution.
+  #
   class DRbIdConv
+    def initialize
+      @id2ref = {}
+      @mutex = Mutex.new
+    end
 
     # Convert an object reference id to an object.
     #
     # This implementation looks up the reference id in the local object
     # space and returns the object it refers to.
     def to_obj(ref)
-      ObjectSpace._id2ref(ref)
+      _get(ref)
     end
 
     # Convert an object into a reference id.
     #
     # This implementation returns the object's __id__ in the local
     # object space.
     def to_id(obj)
-      obj.nil? ? nil : obj.__id__
+      obj.nil? ? nil : _put(obj)
+    end
+
+    def _clean
+      fail unless @mutex.owned?
+      dead = []
+      @id2ref.each {|id,weakref| dead << id unless weakref.weakref_alive?}
+      dead.each {|id| @id2ref.delete(id)}
+    end
+
+    def _put(obj)
+      id = obj.__id__
+      @mutex.lock
+      begin
+        _clean
+        @id2ref[id] = WeakRef.new(obj)
+      ensure
+        @mutex.unlock
+      end
+      id
+    end
+
+    def _get(id)
+      @mutex.lock
+      begin
+        weakref = @id2ref[id]
+        return weakref.__getobj__ if weakref
+      rescue WeakRef::RefError
+        @id2ref.delete id
+      ensure
+        @mutex.unlock
+      end
+      nil
     end
+    private :_clean, :_put, :_get
   end
 
   # Mixin module making an object undumpable or unmarshallable.