Mike, thanks for your information. Each of our HPUX machines has 2 CPUs.
Actually, before post my problem on this mailing list, I tried to search on Google but can't find any hints to solve the problem. Then I tried to browse the stunnel 4.0.5 source code and can't find any hints too.
But I noticed that someone said on some historical newsgroup postings the problem may be related to openssl. Do you think thats true?
I will wait for the version 4.0.6 and hope it can solve my problem.
Cheers, Gavin