SR-4026: dispatch_test_check_evfilt_read_for_fd for epoll

[dgrove-oss]

Implement dispatch_test_check_evfilt_read_for_fd test method
for the event_epoll backend.

[MadCoder]

that seems overly complicated, that thing only checks whether a given fd is readable whcih you can do with a very simple poll() call, you don't need epoll at all.

struct pollfd pfd = {
    .fd = fd,
    .events = EPOLLIN,
};
int rc;
do {
    rc = poll(&pfd, 1, 0);
} while (rc == -1 && errno == EINTR);
return rc == 1

should be it I think. we don't do that on Darwin because poll() actually is heavyweight and uses a short-lived kqueue.

[MadCoder]

you may want to abort if poll returns -1 and the error isn't EINTR btw.

[dgrove-oss]

Thanks; that is much more sensible. I got distracted by trying to use epoll, but you are right there is no reason to do it that way.