1 files changed, 80 insertions, 0 deletions
diff --git a/trunk/lib/weakref.rb b/trunk/lib/weakref.rb
new file mode 100644
index 0000000000..ba39242445
--- /dev/null
+++ b/trunk/lib/weakref.rb
@@ -0,0 +1,80 @@
+# Weak Reference class that does not bother GCing.
+#
+# Usage:
+#   foo = Object.new
+#   foo = Object.new
+#   p foo.to_s			# original's class
+#   foo = WeakRef.new(foo)
+#   p foo.to_s			# should be same class
+#   ObjectSpace.garbage_collect
+#   p foo.to_s			# should raise exception (recycled)
+
+require "delegate"
+require 'thread'
+
+class WeakRef < Delegator
+
+  class RefError < StandardError
+  end
+
+  @@id_map =  {}                # obj -> [ref,...]
+  @@id_rev_map =  {}            # ref -> obj
+  @@mutex = Mutex.new
+  @@final = lambda {|id|
+    @@mutex.synchronize {
+      rids = @@id_map[id]
+      if rids
+	for rid in rids
+	  @@id_rev_map.delete(rid)
+	end
+	@@id_map.delete(id)
+      end
+      rid = @@id_rev_map[id]
+      if rid
+	@@id_rev_map.delete(id)
+	@@id_map[rid].delete(id)
+	@@id_map.delete(rid) if @@id_map[rid].empty?
+      end
+    }
+  }
+
+  def initialize(orig)
+    @__id = orig.object_id
+    ObjectSpace.define_finalizer orig, @@final
+    ObjectSpace.define_finalizer self, @@final
+    @@mutex.synchronize {
+      @@id_map[@__id] = [] unless @@id_map[@__id]
+    }
+    @@id_map[@__id].push self.object_id
+    @@id_rev_map[self.object_id] = @__id
+    super
+  end
+
+  def __getobj__
+    unless @@id_rev_map[self.object_id] == @__id
+      Kernel::raise RefError, "Invalid Reference - probably recycled", Kernel::caller(2)
+    end
+    begin
+      ObjectSpace._id2ref(@__id)
+    rescue RangeError
+      Kernel::raise RefError, "Invalid Reference - probably recycled", Kernel::caller(2)
+    end
+  end
+  def __setobj__(obj)
+  end
+
+  def weakref_alive?
+    @@id_rev_map[self.object_id] == @__id
+  end
+end
+
+if __FILE__ == $0
+#  require 'thread'
+  foo = Object.new
+  p foo.to_s			# original's class
+  foo = WeakRef.new(foo)
+  p foo.to_s			# should be same class
+  ObjectSpace.garbage_collect
+  ObjectSpace.garbage_collect
+  p foo.to_s			# should raise exception (recycled)
+end