recently, i try to use libcurl-7.18.2 + libevent-1.4.4, and i found that the event_del() call failed so much, but event_add() call are all return successfully i use the curl's example code hiperfifo.c, and dump some runtime info to stderr.log below is the beginning part of stderr.log: ============================below====================================== after epoll_init, epollop->(epfd, nevents, nfds) = 3,31999,31999 socket callback: s=8 e=0x805c390 what=IN Adding data: IN socket callback: s=9 e=0x8072820 what=IN Adding data: IN socket callback: s=10 e=0x8088ba0 what=IN Adding data: IN socket callback: s=11 e=0x809ef20 what=IN Adding data: IN socket callback: s=12 e=0x80b52c8 what=IN Adding data: IN socket callback: s=13 e=0x80cb658 what=IN Adding data: IN socket callback: s=14 e=0x80e19e8 what=IN Adding data: IN socket callback: s=15 e=0x80f7d98 what=IN Adding data: IN socket callback: s=16 e=0x810e168 what=IN Adding data: IN socket callback: s=17 e=0x8124548 what=IN Adding data: IN socket callback: s=18 e=0x813a900 what=IN Adding data: IN socket callback: s=19 e=0x8150c90 what=IN Adding data: IN socket callback: s=8 e=0x805c390 what=OUT Changing action from IN to OUT Error: epoll_del: epoll_ctl return false, fd = 8, op = EPOLL_CTL_MOD, epoll_ctl() returns ENOENT     epollop->(epfd, nevents, nfds) = 3,31999,31999 Error: event_del in setsock() return false socket callback: s=9 e=0x8072820 what=OUT Changing action from IN to OUT Error: epoll_del: epoll_ctl return false, fd = 9, op = EPOLL_CTL_MOD, epoll_ctl() returns ENOENT     epollop->(epfd, nevents, nfds) = 3,31999,31999 Error: event_del in setsock() return false ...... ============================above====================================== my input is 3000 different urls >> grep ENOENT stderr.log | wc -l 2002 >> grep EBADF stderr.log | wc -l 1510 is it a epoll_ctl system call 's bug? or libevent misuse the epoll ? hoping for your help sincerely -- <a href="mailto:dengminwen@gmail.com">dengminwen@gmail.com</a>