Hi everrone Problem: When I created SIGEV_THREAD timer, then start it by timer_settime. like this the notify callback in the helper thread 'start' will be run when timer expiration. But when I delete the timer, the notify callback will be run all the same. This is not what i want. In actual use, I encountered a problem. I found that the 'timer_delete' function returns immediately after called. The timer may not perform the delete action. In addition, the SIGEV_SIGNAL timer can be deleted after called the function. So i think the function has different semantics for different types. Is there a way to implement synchronously ? Looking forward to your reply.