ObjectId#generate uses java.bson.types.ObjectId

Delegating ObjectId#generate when running under jruby to the java BSON
library halves the time needed to generate a new object id.

lib/bson/types/object_id.rb

@@ -30,10 +30,6 @@ module BSON
   #
   # @core objectids
   class ObjectId
-    @@lock  = Mutex.new
-    @@index = 0
-    @@hostname_digest = Digest::MD5.digest(Socket.gethostname)[0, 3]
-
     attr_accessor :data
 
     # Create a new object id. If no parameter is given, an id corresponding
@@ -127,7 +123,7 @@ module BSON
     #
     # @return [Mongo::ObjectId]
     def self.from_string(str)
-      raise InvalidObjectId, "illegal ObjectId format" unless legal?(str)
+      raise InvalidObjectId, "illegal ObjectId format: #{str}" unless legal?(str)
       data = []
       12.times do |i|
         data[i] = str[i * 2, 2].to_i(16)
@@ -171,8 +167,31 @@ module BSON
       Time.at(@data.pack("C4").unpack("N")[0]).utc
     end
 
+    def self.machine_id
+      @@machine_id
+    end
+
     private
 
+    if RUBY_PLATFORM =~ /java/
+      @@generator = Java::OrgBsonTypes::ObjectId
+      @@machine_id = [@@generator.genMachineId].pack("N")[0,3]
+
+      def generate(oid_time=nil)
+        data = (oid_time ? @@generator.new(oid_time) : @@generator.new)
+
+        oid = ''
+        oid += [data.timeSecond].pack("N")
+        oid += [data._machine].pack("N")
+        oid += [data._inc].pack("N")
+        oid.unpack("C12")
+      end
+
+    else
+      @@lock  = Mutex.new
+      @@index = 0
+      @@machine_id = Digest::MD5.digest(Socket.gethostname)[0, 3]
+
       # This gets overwritten by the C extension if it loads.
       def generate(oid_time=nil)
         oid = ''
@@ -186,7 +205,7 @@ module BSON
         oid += [t].pack("N")
 
         # 3 bytes machine
-      oid += @@hostname_digest
+        oid += @@machine_id
 
         # 2 bytes pid
         oid += [Process.pid % 0xFFFF].pack("n")
@@ -204,3 +223,4 @@ module BSON
       end
     end
   end
+end

test/bson/object_id_test.rb

@@ -134,8 +134,7 @@ class ObjectIdTest < Test::Unit::TestCase
     time = Time.now.utc
     id   = ObjectId.from_time(time, :unique => true)
 
-    mac_id = Digest::MD5.digest(Socket.gethostname)[0, 3].unpack("C3")
-    assert_equal id.to_a[4, 3], mac_id
+    assert_equal id.to_a[4, 3], ObjectId.machine_id.unpack("C3")
     assert_equal time.to_i, id.generation_time.to_i
 
     id2 = ObjectId.new(nil, time)