how to deal with this case: andorid epoll_wait return -1 and errno=4 used ndk

Question

I am writing network communication program with Android ndk, using epoll. I found the method ‘epoll_wait’ woken not very accurate

while(1){
    struct epoll_event events[3];
    log_string("epoll_wait start");//here will print start time
    events_len = epoll_wait(_epoll_fd, events, 3, 20 * 1000);// wait 20 second,for test,I use pipe instead of socket,monitor a pipe EPOLLIN event
    if (events_len <= 0) {
        log_string("epoll_wait end events_len=%d,errno=%d", events_len, errno);//Normally,the events_len always is 0,and errno is 0
    }
}

The above code runs on the PC(like Ubuntun PC) is very normal,as expected.

If it runs on Android Phone（use Android Service , separate thread to run） is as expected at first.

After some time,epoll_wait becomes not very accurate,sometimes got -1 and errno=4,sometimes waited very long.

So I only know that phenomenon, but do not know why.

Can you tell why and tell me the best practices for use android epoll? thx

Answer 1

4 is EINTR, which means your app got a signal. This isn't really an error, just restart epoll.

Regarding "waited very long", does your app hold at least a partial wakelock?