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Diffstat (limited to 'ev_epoll.c')
-rw-r--r--ev_epoll.c86
1 files changed, 70 insertions, 16 deletions
diff --git a/ev_epoll.c b/ev_epoll.c
index bb56218..52f8337 100644
--- a/ev_epoll.c
+++ b/ev_epoll.c
@@ -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))