Wait nccl all reduce

paddle/fluid/framework/parallel_executor.cc

@@ -348,6 +348,11 @@ struct NCCLAllReduceOpHandle : public OpHandle {
   explicit NCCLAllReduceOpHandle(ParallelExecutorPrivate *member)
       : member_(member) {}
 
+  void Wait(platform::DeviceContext *waited_dev) override {
+    VLOG(3) << "Wait nccl all reduce op";
+    OpHandle::Wait(waited_dev);
+  }
+
  protected:
   void RunImpl() override {
     if (this->inputs_.size() == 1) {
@@ -381,7 +386,6 @@ struct NCCLAllReduceOpHandle : public OpHandle {
         if (numel == 0) {
           numel = static_cast<size_t>(lod_tensor.numel());
         }
-
         auto &nccl_ctx = member_->communication_streams_.at(dev_id);
         PADDLE_ENFORCE(platform::dynload::ncclAllReduce(
             buffer, buffer, numel, static_cast<ncclDataType_t>(dtype), ncclSum,