diff options
| -rw-r--r-- | ev_epoll.c | 86 |
1 files changed, 70 insertions, 16 deletions
@@ -29,23 +29,64 @@ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ +/* + * general notes about epoll: + * + * a) epoll silently removes fds from the fd set. as nothing tells us + * that an fd has been removed otherwise, we have to continually + * "rearm" fds that we suspect *might* have changed (same + * problem with kqueue, but much less costly there). + * b) the fact that ADD != MOD creates a lot of extra syscalls due to a) + * and seems not to have any advantage. + * c) the inability to handle fork or file descriptors (think dup) + * limits the applicability over poll, so this is not a generic + * poll replacement. + * + * lots of "weird code" and complication handling in this file is due + * to these design problems with epoll, as we try very hard to avoid + * epoll_ctl syscalls for common usage patterns. + */ + #include <sys/epoll.h> static void epoll_modify (EV_P_ int fd, int oev, int nev) { - int mode = nev ? oev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD : EPOLL_CTL_DEL; - struct epoll_event ev; + + /* + * we handle EPOLL_CTL_DEL by ignoring it here + * on the assumption that the fd is gone anyways + * if that is wrong, we have to handle the spurious + * event in epoll_poll. + */ + if (!nev) + return; + ev.data.u64 = fd; /* use u64 to fully initialise the struct, for nicer strace etc. */ - ev.events = - (nev & EV_READ ? EPOLLIN : 0) - | (nev & EV_WRITE ? EPOLLOUT : 0); - - if (expect_false (epoll_ctl (backend_fd, mode, fd, &ev))) - if (errno != ENOENT /* on ENOENT the fd went away, so try to do the right thing */ - || (nev && epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))) - fd_kill (EV_A_ fd); + ev.events = (nev & EV_READ ? EPOLLIN : 0) + | (nev & EV_WRITE ? EPOLLOUT : 0); + + if (expect_true (!epoll_ctl (backend_fd, oev ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &ev))) + return; + + if (expect_true (errno == ENOENT)) + { + /* on ENOENT the fd went away, so try to do the right thing */ + if (!nev) + return; + + if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev)) + return; + } + else if (expect_true (errno == EEXIST)) + { + /* on EEXIST we ignored a previous DEL */ + if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev)) + return; + } + + fd_kill (EV_A_ fd); } static void @@ -63,12 +104,25 @@ epoll_poll (EV_P_ ev_tstamp timeout) } for (i = 0; i < eventcnt; ++i) - fd_event ( - EV_A_ - epoll_events [i].data.u64, - (epoll_events [i].events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0) - | (epoll_events [i].events & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0) - ); + { + struct epoll_event *ev = epoll_events + i; + + int fd = ev->data.u64; + int got = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0) + | (ev->events & (EPOLLIN | EPOLLERR | EPOLLHUP) ? EV_READ : 0); + int want = anfds [fd].events; + + if (expect_false (got & ~want)) + { + /* we received an event but are not interested in it, try mod or del */ + ev->events = (want & EV_READ ? EPOLLIN : 0) + | (want & EV_WRITE ? EPOLLOUT : 0); + + epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev); + } + + fd_event (EV_A_ fd, got); + } /* if the receive array was full, increase its size */ if (expect_false (eventcnt == epoll_eventmax)) |