RUBY-167 Cursor#alive?

lib/mongo/cursor.rb

@@ -93,6 +93,18 @@ module Mongo
       end
     end
 
+    # Guess whether the cursor is alive on the server.
+    #
+    # Note that this method only checks whether we have
+    # a cursor id. The cursor may still have timed out
+    # on the server. This will be indicated in the next
+    # call to Cursor#next_document.
+    #
+    # @return [Boolean]
+    def alive?
+      @cursor_id && @cursor_id != 0
+    end
+
     # Get the next document specified the cursor options.
     #
     # @return [Hash, Nil] the next document or Nil if no documents remain.

test/cursor_test.rb

@@ -16,6 +16,22 @@ class CursorTest < Test::Unit::TestCase
     @@coll_full_name = "#{MONGO_TEST_DB}.test"
   end
 
+  def test_alive
+    batch = []
+    5000.times do |n|
+      batch << {:a => n}
+    end
+
+    @@coll.insert(batch)
+    cursor = @@coll.find
+    assert !cursor.alive?
+    cursor.next
+    assert cursor.alive?
+    cursor.close
+    assert !cursor.alive?
+    @@coll.remove
+  end
+
   def test_add_options
     c = @@coll.find
     c.add_option(OP_QUERY_EXHAUST)