diff --git a/src/engine_base.cc b/src/engine_base.cc
index 00ac1cffb..eec2330fc 100644
--- a/src/engine_base.cc
+++ b/src/engine_base.cc
@@ -174,8 +174,7 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
   // if no childs, no need to reduce
   if (nlink == static_cast<int>(parent_index != -1)) {
     size_up_reduce = total_size;
-  }
-  
+  }  
   // while we have not passed the messages out
   while (true) {
     // select helper
@@ -184,7 +183,10 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
     for (int i = 0; i < nlink; ++i) {
       if (i == parent_index) {
         if (size_down_in != total_size) {
-          selecter.WatchRead(links[i].sock); finished = false;
+          selecter.WatchRead(links[i].sock);
+          // only watch for exception in live channels
+          selecter.WatchException(links[i].sock);
+          finished = false;
         }
         if (size_up_out != total_size) {
           selecter.WatchWrite(links[i].sock);
@@ -193,11 +195,15 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
         if (links[i].size_read != total_size) {
           selecter.WatchRead(links[i].sock);
         }
+        // size_write <= size_read 
         if (links[i].size_write != total_size) {
-          selecter.WatchWrite(links[i].sock); finished = false;
+          selecter.WatchWrite(links[i].sock);
+          // only watch for exception in live channels
+          selecter.WatchException(links[i].sock);
+          finished = false;
         }
       }
-      selecter.WatchException(links[i].sock);        
+
     }
     // finish runing allreduce
     if (finished) break;