RUBY-184 fsync lock helpers

lib/mongo/connection.rb

@@ -211,6 +211,24 @@ module Mongo
       end
     end
 
+    # Fsync, then lock the mongod process against writes. Use this to get
+    # the datafiles in a state safe for snapshotting, backing up, etc.
+    #
+    # @return [BSON::OrderedHash] the command response
+    def lock!
+      cmd = BSON::OrderedHash.new
+      cmd[:fsync] = 1
+      cmd[:lock]  = true
+      self['admin'].command(cmd)
+    end
+
+    # Unlock a previously fsync-locked mongod process.
+    #
+    # @return [BSON::OrderedHash] command response
+    def unlock!
+      self['admin']['$cmd.sys.unlock'].find_one
+    end
+
     # Apply each of the saved database authentications.
     #
     # @return [Boolean] returns true if authentications exist and succeeed, false

test/connection_test.rb

@@ -143,6 +143,24 @@ class TestConnection < Test::Unit::TestCase
     end
   end
 
+  def test_fsync_lock
+    @mongo.lock!
+    assert_equal 1, @mongo['admin']['$cmd.sys.inprog'].find_one['fsyncLock'], "Not fsync-locked"
+    assert_equal "unlock requested", @mongo.unlock!['info']
+    unlocked = false
+    counter  = 0
+    while counter < 5
+      if @mongo['admin']['$cmd.sys.inprog'].find_one['fsyncLock'].nil?
+        unlocked = true
+        break
+      else
+        sleep(1)
+        counter += 1
+      end
+    end
+    assert unlocked, "mongod failed to unlock"
+  end
+
   context "Saved authentications" do
     setup do
       @conn = Mongo::Connection.new