when I use below command at nginx host the command is block and nothing is back.
curl http://localhost

and below is trace of nginx thread(with strace -p thread):

{si_signo=SIGRT_11, si_code=0x1, si_pid=65, si_uid=6, si_value={int=1, ptr=0x1}}, 0, 8) = 43
rt_sigtimedwait([ALRM IO RT_11 RT_12],