I added __sync_synchronize calls before semaphore Post() and after Wait(): https://github.com/alja/xrootd/commit/afac030d21a81de70a9ad4ccb044c69cb065c2ec This did not fix the problem. There helgrind reports were the same. -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/xrootd/xrootd/issues/404#issuecomment-241121244 ######################################################################## Use REPLY-ALL to reply to list To unsubscribe from the XROOTD-DEV list, click the following link: https://listserv.slac.stanford.edu/cgi-bin/wa?SUBED1=XROOTD-DEV&A=1