diff --git a/src/engine_base.cc b/src/engine_base.cc
index 9f0aaa405..00ac1cffb 100644
--- a/src/engine_base.cc
+++ b/src/engine_base.cc
@@ -179,12 +179,28 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
   // while we have not passed the messages out
   while (true) {
     // select helper
+    bool finished = true;
     utils::SelectHelper selecter;
-    for (size_t i = 0; i < links.size(); ++i) {
-      selecter.WatchRead(links[i].sock);
-      selecter.WatchWrite(links[i].sock);
+    for (int i = 0; i < nlink; ++i) {
+      if (i == parent_index) {
+        if (size_down_in != total_size) {
+          selecter.WatchRead(links[i].sock); finished = false;
+        }
+        if (size_up_out != total_size) {
+          selecter.WatchWrite(links[i].sock);
+        }
+      } else {
+        if (links[i].size_read != total_size) {
+          selecter.WatchRead(links[i].sock);
+        }
+        if (links[i].size_write != total_size) {
+          selecter.WatchWrite(links[i].sock); finished = false;
+        }
+      }
       selecter.WatchException(links[i].sock);        
     }
+    // finish runing allreduce
+    if (finished) break;
     // select must return 
     selecter.Select();
     // exception handling
@@ -261,19 +277,12 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
       // this is root, can use reduce as most recent point
       size_down_in = size_up_out = size_up_reduce;
     }
-    // check if we finished the job of message passing
-    size_t nfinished = size_down_in;
     // can pass message down to childs
     for (int i = 0; i < nlink; ++i) {
-      if (i != parent_index) {
-        if (selecter.CheckWrite(links[i].sock)) {
-          if (!links[i].WriteFromArray(sendrecvbuf, size_down_in)) return kSockError;
-        }
-        nfinished = std::min(links[i].size_write, nfinished);
+      if (i != parent_index && selecter.CheckWrite(links[i].sock)) {
+        if (!links[i].WriteFromArray(sendrecvbuf, size_down_in)) return kSockError;
       }
     }
-    // check boundary condition
-    if (nfinished >= total_size) break;
   }
   return kSuccess;  
 }
@@ -288,6 +297,7 @@ AllReduceBase::TryAllReduce(void *sendrecvbuf_,
 AllReduceBase::ReturnType
 AllReduceBase::TryBroadcast(void *sendrecvbuf_, size_t total_size, int root) {
   if (links.size() == 0 || total_size == 0) return kSuccess;
+  utils::Check(root < world_size, "Broadcast: root should be smaller than world size");
   // number of links
   const int nlink = static_cast<int>(links.size());
   // size of space already read from data
@@ -306,13 +316,25 @@ AllReduceBase::TryBroadcast(void *sendrecvbuf_, size_t total_size, int root) {
   }  
   // while we have not passed the messages out
   while(true) {
+    bool finished = true;
     // select helper
     utils::SelectHelper selecter;
-    for (size_t i = 0; i < links.size(); ++i) {
-      selecter.WatchRead(links[i].sock);
-      selecter.WatchWrite(links[i].sock);
+    for (int i = 0; i < nlink; ++i) {
+      if (in_link == -2) {
+        selecter.WatchRead(links[i].sock); finished = false;
+      }
+      if (i == in_link && links[i].size_read != total_size) {
+        selecter.WatchRead(links[i].sock); finished = false;
+      }
+      if (in_link != -2 && i != in_link && links[i].size_write != total_size) {
+        selecter.WatchWrite(links[i].sock); finished = false;
+      }
       selecter.WatchException(links[i].sock);        
     }
+    // finish running
+    if (finished) break;
+    // select
+    selecter.Select();
     // exception handling
     for (int i = 0; i < nlink; ++i) {
         // recive OOB message from some link 
@@ -336,18 +358,12 @@ AllReduceBase::TryBroadcast(void *sendrecvbuf_, size_t total_size, int root) {
         size_in = links[in_link].size_read;
       }
     }
-    size_t nfinished = total_size;
     // send data to all out-link
     for (int i = 0; i < nlink; ++i) {
-      if (i != in_link) {
-        if (selecter.CheckWrite(links[i].sock)) {
-          if (!links[i].WriteFromArray(sendrecvbuf_, size_in)) return kSockError;
-        }
-        nfinished = std::min(nfinished, links[i].size_write);
+      if (i != in_link && selecter.CheckWrite(links[i].sock)) {
+        if (!links[i].WriteFromArray(sendrecvbuf_, size_in)) return kSockError;
       }
     }
-    // check boundary condition
-    if (nfinished >= total_size) break;
   }
   return kSuccess;
 }
diff --git a/src/engine_robust.cc b/src/engine_robust.cc
index 7f510d2f3..9f03bea5e 100644
--- a/src/engine_robust.cc
+++ b/src/engine_robust.cc
@@ -366,10 +366,10 @@ AllReduceRobust::TryRecoverData(RecoverType role,
     // do not need to provide data or receive data, directly exit
     if (!req_data) return kSuccess;
   }
+  utils::Assert(recv_link >= 0 || role == kHaveData, "recv_link must be active");
   for (int i = 0; i < nlink; ++i) {
     links[i].ResetSize();
   }
-  utils::Assert(recv_link >= 0 || role == kHaveData, "recv_link must be active");
   if (role == kPassData) {
     links[recv_link].InitBuffer(1, size, reduce_buffer_size);
   }
diff --git a/test/test_allreduce.cpp b/test/test_allreduce.cpp
index 3a2cc2a9d..02cb4057f 100644
--- a/test/test_allreduce.cpp
+++ b/test/test_allreduce.cpp
@@ -70,6 +70,7 @@ int main(int argc, char *argv[]) {
   int n = atoi(argv[1]);
   sync::Init(argc, argv);
   int rank = sync::GetRank();
+  int nproc = sync::GetWorldSize();
   std::string name = sync::GetProcessorName();
 
   test::Mock mock(rank, argv[2], argv[3]);
@@ -79,6 +80,10 @@ int main(int argc, char *argv[]) {
   utils::LogPrintf("[%d] !!!TestMax pass\n", rank);
   TestSum(mock, n);
   utils::LogPrintf("[%d] !!!TestSum pass\n", rank);
+  for (int i = 0; i < nproc; i += nproc / 3) {
+    TestBcast(mock, n, i);
+  }
+  utils::LogPrintf("[%d] !!!TestBcast pass\n", rank);
   sync::Finalize();
   printf("[%d] all check pass\n", rank);
   return 0;