Add weakhash back in

lib/sbdb/weakhash.rb

@@ -0,0 +1,59 @@
+module SBDB
+  # See http://eigenclass.org/hiki/deferred-finalizers-in-Ruby
+  # Not threadsafe.
+  class WeakHash
+  	attr_reader :cache
+  	def initialize cache = ::Hash.new
+  		@cache = cache
+  		@key_map = {}
+  		@rev_cache = ::Hash.new { |h,k| h[k] = {} }
+  		@reclaim_value = lambda do |value_id| 
+  			if @rev_cache.has_key? value_id
+  				@rev_cache[value_id].each_key{ |key| @cache.delete key }
+  				@rev_cache.delete value_id
+  			end
+  		end
+  		@reclaim_key = lambda do |key_id|
+  			@cache.delete @key_map.delete(key_id) if @key_map.has_key? key_id
+  		end
+  	end
+
+  	def []=(key, value)
+  		case key
+  		when Fixnum, Symbol, true, false
+  			key2 = key
+  		else
+  			key2 = key.dup
+  		end
+  		@rev_cache[value.object_id][key2] = true
+  		@cache[key2] = value.object_id
+  		@key_map[key.object_id] = key2
+
+  		ObjectSpace.define_finalizer(value, @reclaim_value)
+  		ObjectSpace.define_finalizer(key, @reclaim_key)
+  		value
+  	end
+
+  	def [](key)
+  		value_id = @cache[key]
+  		return ObjectSpace._id2ref(value_id)  unless value_id.nil?
+  		nil
+  	rescue RangeError
+  		nil
+  	end
+
+  	def each(&e)
+  		@cache.each do |k, vid|
+  			unless vid.nil?
+  				obj =
+  				  begin
+  						ObjectSpace._id2ref vid
+  					rescue RangeError
+  						next
+  					end
+  				yield k, obj
+  			end
+  		end
+  	end
+  end
+end