diff --git a/Network/C10kServer.hs b/Network/C10kServer.hs
--- a/Network/C10kServer.hs
+++ b/Network/C10kServer.hs
@@ -7,12 +7,8 @@
   server can handle 'preforkProcessNumber' * 'threadNumberPerProcess'
   connections.
 
-  Programs complied by GHC 6.10 or earlier with the -threaded option
-  kill the IO thread when forkProcess is used. So, don't specify
-  the -threaded option to use this library.
-
-  Even if GHC 6.14 supports kqueue or epoll(), it is difficult for RTS
-  to balance over multi-cores. So, this library can be used to
+  GHC 7 supports kqueue or epoll() but it is difficult
+  to balance over multi-core. So, this library can be used to
   make a process for each core and to set limitation of the number
   to accept connections.
 
@@ -29,13 +25,14 @@
 import Control.Concurrent
 import Control.Exception
 import Control.Monad
-import System.IO
+import Data.IORef
 import Network.BSD
 import Network.Socket
-import Prelude hiding (catch)
-import Network.TCPInfo hiding (accept)
 import qualified Network.TCPInfo as T (accept)
+import Network.TCPInfo hiding (accept)
+import Prelude hiding (catch)
 import System.Exit
+import System.IO
 import System.Posix.Process
 import System.Posix.Signals
 import System.Posix.Types
@@ -150,7 +147,7 @@
     handleSignal cids = do
         ignoreSigChild
         mapM_ (terminator cids) [sigTERM,sigINT]
-    pause = awaitSignal Nothing >> yield
+    pause = blockSignals reservedSignals >> awaitSignal Nothing >> yield
     initHandler func sig = installHandler sig func Nothing
     ignoreSigChild = initHandler Ignore sigCHLD
     terminator cids = initHandler (Catch (terminateChildren cids))
@@ -194,20 +191,20 @@
 runServer :: Dispatch -> C10kConfig -> IO ()
 runServer dispatch cnf = do
     startedHook cnf
-    mvar <- newMVar 0
-    dispatchOrSleep mvar dispatch cnf
+    ref <- newIORef 0 :: IO (IORef Int)
+    dispatchOrSleep ref dispatch cnf
 
-dispatchOrSleep :: MVar Int -> Dispatch -> C10kConfig -> IO ()
-dispatchOrSleep mvar dispatch cnf = do
+dispatchOrSleep :: IORef Int -> Dispatch -> C10kConfig -> IO ()
+dispatchOrSleep ref dispatch cnf = do
     n <- howMany
     if n > threadNumberPerProcess cnf
         then sleep (sleepTimer cnf * microseconds)
         else dispatch increase decrease
-    dispatchOrSleep mvar dispatch cnf
+    dispatchOrSleep ref dispatch cnf
   where
-    howMany = readMVar mvar
-    increase = modifyMVar_ mvar (return . succ)
-    decrease = modifyMVar_ mvar (return . pred)
+    howMany = readIORef ref
+    increase = atomicModifyIORef ref (\n -> (n+1,()))
+    decrease = atomicModifyIORef ref (\n -> (n-1,()))
     sleep = threadDelay
 
 ----------------------------------------------------------------
@@ -248,10 +245,11 @@
           , addrSocketType = Stream
           , addrProtocol = proto
           }
-    ais <- getAddrInfo (Just hints) maddr (Just serv)
-    let ai = head ais
-    sock <- socket (addrFamily ai) (addrSocketType ai) (addrProtocol ai)
+    addrs <- getAddrInfo (Just hints) maddr (Just serv)
+    let addrs' = filter (\x -> addrFamily x == AF_INET6) addrs
+        addr = if null addrs' then head addrs else head addrs'
+    sock <- socket (addrFamily addr) (addrSocketType addr) (addrProtocol addr)
     setSocketOption sock ReuseAddr 1
-    bindSocket sock (addrAddress ai)
+    bindSocket sock (addrAddress addr)
     listen sock maxListenQueue
     return sock
diff --git a/c10k.cabal b/c10k.cabal
--- a/c10k.cabal
+++ b/c10k.cabal
@@ -1,5 +1,5 @@
 Name:                   c10k
-Version:                0.4.1
+Version:                0.5.0
 Author:                 Kazu Yamamoto <kazu@iij.ad.jp>
 Maintainer:             Kazu Yamamoto <kazu@iij.ad.jp>
 License:                BSD3
@@ -20,12 +20,12 @@
 Build-Type:             Simple
 Library
   if impl(ghc >= 6.12)
-    GHC-Options:        -Wall -O2 -fno-warn-unused-do-bind
+    GHC-Options:        -Wall -fno-warn-unused-do-bind
   else
-    GHC-Options:        -Wall -O2
+    GHC-Options:        -Wall
   Exposed-Modules:      Network.C10kServer
                         Network.TCPInfo
-  Build-Depends:        base >= 4 && < 5, haskell98, network, unix
+  Build-Depends:        base >= 4 && < 5, network, unix
 Source-Repository head
   Type:                 git
   Location:             git://github.com/kazu-yamamoto/c10k.git