Make sure watcher.set() isn't being called when active

lib/dns.js

@@ -14,9 +14,8 @@ timer.callback = function () {
   for (var i = 0, l = sockets.length; i < l; i++) {
     var socket = sockets[i];
     var s = parseInt(socket, 10);
-    channel.processFD( watchers[socket].read  ? s : dns.SOCKET_BAD
-                     , watchers[socket].write ? s : dns.SOCKET_BAD
-                     );
+    channel.processFD(watchers[socket].read  ? s : dns.SOCKET_BAD,
+                      watchers[socket].write ? s : dns.SOCKET_BAD);
   }
   updateTimer();
 };
@@ -46,20 +45,19 @@ var channel = new dns.Channel({SOCK_STATE_CB: function (socket, read, write) {
                        };
 
     watcher.callback = function(read, write)  {
-      channel.processFD( read  ? socket : dns.SOCKET_BAD
-                       , write ? socket : dns.SOCKET_BAD
-                       );
+      channel.processFD(read  ? socket : dns.SOCKET_BAD,
+                        write ? socket : dns.SOCKET_BAD);
       updateTimer();
     };
   };
 
-  watcher.set(socket, read == 1, write == 1);
+  watcher.stop();
 
   if (!(read || write)) {
-    watcher.stop();
     delete activeWatchers[socket];
     return;
   } else {
+    watcher.set(socket, read == 1, write == 1);
     watcher.start();
     activeWatchers[socket] = watcher;
   }

src/node_io_watcher.cc

@@ -139,6 +139,7 @@ Handle<Value> IOWatcher::Set(const Arguments& args) {
 
   if (args[2]->IsTrue()) events |= EV_WRITE;
 
+  assert(!io->watcher_.active);
   ev_io_set(&io->watcher_, fd, events);
 
   return Undefined();