Fix race condition in FileFetcher

Author: shahor02

Common/Utils/include/CommonUtils/FileFetcher.h

@@ -104,6 +104,7 @@ class FileFetcher
   size_t mNFilesProc = 0;
   size_t mNFilesProcOK = 0;
   mutable std::mutex mMtx;
+  std::mutex mMtxStop;
   std::thread mFetcherThread{};
 
   ClassDefNV(FileFetcher, 1);

Common/Utils/src/FileFetcher.cxx

@@ -196,6 +196,7 @@ void FileFetcher::start()
 void FileFetcher::stop()
 {
   mRunning = false;
+  std::lock_guard<std::mutex> lock(mMtxStop);
   if (mFetcherThread.joinable()) {
     mFetcherThread.join();
   }