node.js - I'm confused with the epoll in libuv network I/O -

these days i'm reading source code of node.js, here i'm confused:

in libuv's uv__io_poll function, firstly, in while loop pool out every i/o watchers , events interseted about, , run uv__epoll_ctl() register events system's epoll.

while (!queue_empty(&loop->watcher_queue)) {     q = queue_head(&loop->watcher_queue);     queue_remove(q);     queue_init(q);      w = queue_data(q, uv__io_t, watcher_queue);     assert(w->pevents != 0);     assert(w->fd >= 0);     assert(w->fd < (int) loop->nwatchers);      e.events = w->pevents;     e.data = w->fd;      if (w->events == 0)       op = uv__epoll_ctl_add;     else       op = uv__epoll_ctl_mod;     if (uv__epoll_ctl(loop->backend_fd, op, w->fd, &e)) {       if (errno != eexist)         abort();       if (uv__epoll_ctl(loop->backend_fd, uv__epoll_ctl_mod, w->fd, &e))         abort();     }      w->events = w->pevents;   } 

and in infinite loop run uv__epoll_wait() wait events coming:

for(;;){     nfds = uv__epoll_wait(loop->backend_fd,                                 events,                                 array_size(events),                                 timeout);     //... run callback every events. } 

but function blocked loop. if there comes new watchers loop->watcher_queuue, can't registered in time.

so how epool work ensure while (!queue_empty(&loop->watcher_queue)){} can run again in time(it means goto next event loop).

how long every event loop runs?