Wait multiple stream

paddle/fluid/framework/parallel_executor.cc

@@ -816,6 +816,10 @@ void ParallelExecutor::Run(const std::vector<std::string> &fetch_tensors,
   // FIXME:
   // It could be optimized by using multiple events in an operator.
   // Manually sync computation during iter.
+  for (auto &s : member_->communication_streams_) {
+    s.second.ctx_->Wait();
+  }
+
   for (auto &p : member_->places_) {
     platform::DeviceContextPool::Instance().Get(p)->Wait();
   }