diff --git a/shadowsocks/event.py b/shadowsocks/event.py
index 737d039..2cdd065 100644
--- a/shadowsocks/event.py
+++ b/shadowsocks/event.py
@@ -29,6 +29,9 @@ import select
 from collections import defaultdict
 
 
+__all__ = ['EventLoop', 'MODE_NULL', 'MODE_IN', 'MODE_OUT', 'MODE_ERR',
+           'MODE_HUP', 'MODE_NVAL']
+
 MODE_NULL = 0x00
 MODE_IN = 0x01
 MODE_OUT = 0x04
@@ -135,13 +138,37 @@ class SelectLoop(object):
         self.add_fd(fd, mode)
 
 
-EventLoop = None
-
-if hasattr(select, 'epoll'):
-    EventLoop = EpollLoop
-elif hasattr(select, 'kqueue'):
-    EventLoop = KqueueLoop
-elif hasattr(select, 'select'):
-    EventLoop = SelectLoop
-else:
-    raise Exception('can not find any available functions in select package')
+class EventLoop(object):
+    def __init__(self):
+        if hasattr(select, 'epoll'):
+            self._impl = EpollLoop()
+        elif hasattr(select, 'kqueue'):
+            self._impl = KqueueLoop()
+        elif hasattr(select, 'select'):
+            self._impl = SelectLoop()
+        else:
+            raise Exception('can not find any available functions in select '
+                            'package')
+        self._fd_to_f = defaultdict(list)
+
+    def poll(self, timeout=None):
+        events = self._impl.poll(timeout)
+        return ((self._fd_to_f[fd], event) for fd, event in events)
+
+    def add(self, f, mode):
+        fd = f.fileno()
+        self._fd_to_f[fd].append(f)
+        self._impl.add_fd(fd, mode)
+
+    def remove(self, f):
+        fd = f.fileno()
+        a = self._fd_to_f[fd]
+        if len(a) <= 1:
+            self._fd_to_f[fd] = None
+        else:
+            a.remove(f)
+        self._impl.remove_fd(fd)
+
+    def modify(self, f, mode):
+        fd = f.fileno()
+        self._impl.modify_fd(fd, mode)
diff --git a/shadowsocks/udprelay.py b/shadowsocks/udprelay.py
index 841c035..819c874 100644
--- a/shadowsocks/udprelay.py
+++ b/shadowsocks/udprelay.py
@@ -84,6 +84,7 @@ class UDPRelay(object):
         self._timeout = timeout
         self._is_local = is_local
         self._eventloop = event.EventLoop()
+        self._cache = {}  # TODO replace this dictionary with an LRU cache
 
     def _handle_server(self, addr, sock, data):
         # TODO
@@ -96,7 +97,7 @@ class UDPRelay(object):
     def _run(self):
         eventloop = self._eventloop
         server_socket = self._server_socket
-        eventloop.add_fd(server_socket, event.MODE_IN)
+        eventloop.add(server_socket, event.MODE_IN)
         is_local = self._is_local
         while True:
             r = eventloop.poll()