fix bug that finish_set_filelist failed in multithread

paddle/fluid/framework/data_feed.cc

@@ -41,6 +41,7 @@ namespace framework {
 std::vector<std::string> DataFeed::filelist_;
 size_t DataFeed::file_idx_;
 std::mutex DataFeed::mutex_for_pick_file_;
+bool DataFeed::finish_set_filelist_;
 
 void DataFeed::AddFeedVar(Variable* var, const std::string& name) {
   CheckInit();

paddle/fluid/framework/data_feed.h

@@ -205,7 +205,7 @@ class DataFeed {
   int batch_size_;
 
   bool finish_init_;
-  bool finish_set_filelist_;
+  static bool finish_set_filelist_;
   bool finish_binding_memory_;
   bool finish_start_;
 };