Databases
StackOverflow2013
Postsdbo
POlinux - Can't get eventfd to work with epoll together
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POlinux - Can't get eventfd to work with epoll together
    primarykey
    data
    text
    <p>I'm writing a simple server class based on epoll. In order to wake up <code>epoll_wait()</code>, I decided to use an eventfd. It is said that it is better suited for simple event communication and I agree with that. So I created my event and put a watch on it:</p> <pre><code>_epollfd = epoll_create1(0); if (_epollfd == -1) throw ServerError("epoll_create"); _eventfd = eventfd(0, EFD_NONBLOCK); epoll_event evnt = {0}; evnt.data.fd = _eventfd; evnt.events = _events; if (epoll_ctl(_epollfd, EPOLL_CTL_ADD, _eventfd, &amp;evnt) == -1) throw ServerError("epoll_ctl(add)"); </code></pre> <p>later in the message waiting loop, on a separate thread:</p> <pre><code> int count = epoll_wait(_epollfd, evnts, EVENTS, -1); if (count == -1) { if (errno != EINTR) { perror("epoll_wait"); return; } } for (int i = 0; i &lt; count; ++i) { epoll_event &amp; e = evnts[i]; if (e.data.fd == _serverSock) connectionAccepted(); else if (e.data.fd == _eventfd) { eventfd_t val; eventfd_read(_eventfd, &amp;val); return; } } </code></pre> <p>and, of course, the code that stop the server was:</p> <pre><code>eventfd_write(_eventfd, 1); </code></pre> <p>For reasons that I can't explain, I was unable to wake up the <code>epoll_wait()</code> just by writing to the event. Eventually, this worked in a few debugging sessions.</p> <p>Here is my workaround: knowing that <code>EPOLLOUT</code> will trigger an event every time the fd is available for writing, I changed the stop code to</p> <pre><code>epoll_event evnt = {0}; evnt.data.fd = _eventfd; evnt.events = EPOLLOUT; if (epoll_ctl(_epollfd, EPOLL_CTL_MOD, _eventfd, &amp;evnt) == -1) throw ServerError("epoll_ctl(mod)"); </code></pre> <p>Now it works but It shouldn't be this way.</p> <p>I don't believe this should be any difficult. What have I done wrong?</p> <p>Thanks</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USuser666412
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POlinux - Can't get eventfd to work with epoll together
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POlinux - Can't get eventfd to work with epoll together
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POlinux - Can't get eventfd to work with epoll together
      1. USlithiumhead
      1. VTFavorite
    1. COWhat is `_events` initialised to?
      singulars
      1. POlinux - Can't get eventfd to work with epoll together
      1. UScaf
    2. CO_events was set as EPOLLIN | EPOLLET
      singulars
      1. POlinux - Can't get eventfd to work with epoll together
      1. USuser666412
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload