--- a/util/channel.h 2022-01-10 03:06:56.580066258 +0800
+++ b/util/channel.h 2022-01-10 03:06:46.337071094 +0800
@@ -60,7 +60,7 @@

  private:
   std::condition_variable cv_;
-  std::mutex lock_;
+  mutable std::mutex lock_;
   std::queue<T> buffer_;
   bool eof_;
 };