diff -r f37c2dd33031 -r 4698900b8221 src/share/vm/utilities/ostream.hpp
--- a/src/share/vm/utilities/ostream.hpp	Mon Nov 18 23:41:06 2019 -0500
+++ b/src/share/vm/utilities/ostream.hpp	Thu Apr 09 13:07:11 2020 +0000
@@ -235,11 +235,15 @@
   void flush() {};
 };
 
+class Mutex;
 class gcLogFileStream : public fileStream {
  protected:
   const char*  _file_name;
   jlong  _bytes_written;
   uintx  _cur_file_num;             // current logfile rotation number, from 0 to NumberOfGCLogFiles-1
+ private:
+  Mutex* _file_lock;
+  void rotate_log_impl(bool force, outputStream* out);
  public:
   gcLogFileStream(const char* file_name);
   ~gcLogFileStream();