ev_epoll.c in rev-0.2.3

- old
+ new

@@ -50,53 +50,71 @@
  *    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.
+ * epoll_ctl syscalls for common usage patterns and handle the breakage
+ * ensuing from receiving events for closed and otherwise long gone
+ * file descriptors.
  */
 
 #include <sys/epoll.h>
 
 static void
 epoll_modify (EV_P_ int fd, int oev, int nev)
 {
   struct epoll_event ev;
+  unsigned char oldmask;
 
   /*
    * 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 the fd is added again, we try to ADD it, and, if that
+   * fails, we assume it still has the same eventmask.
    */
   if (!nev)
     return;
 
-  ev.data.u64 = fd; /* use u64 to fully initialise the struct, for nicer strace etc. */
+  oldmask = anfds [fd].emask;
+  anfds [fd].emask = nev;
+
+  /* store the generation counter in the upper 32 bits, the fd in the lower 32 bits */
+  ev.data.u64 = (uint64_t)(uint32_t)fd
+              | ((uint64_t)(uint32_t)++anfds [fd].egen << 32);
   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 ENOENT then the fd went away, so try to do the right thing */
       if (!nev)
-        return;
+        goto dec_egen;
 
       if (!epoll_ctl (backend_fd, EPOLL_CTL_ADD, fd, &ev))
         return;
     }
   else if (expect_true (errno == EEXIST))
     {
-      /* on EEXIST we ignored a previous DEL */
+      /* EEXIST means we ignored a previous DEL, but the fd is still active */
+      /* if the kernel mask is the same as the new mask, we assume it hasn't changed */
+      if (oldmask == nev)
+        goto dec_egen;
+
       if (!epoll_ctl (backend_fd, EPOLL_CTL_MOD, fd, &ev))
         return;
     }
 
   fd_kill (EV_A_ fd);
+
+dec_egen:
+  /* we didn't successfully call epoll_ctl, so decrement the generation counter again */
+  --anfds [fd].egen;
 }
 
 static void
 epoll_poll (EV_P_ ev_tstamp timeout)
 {
@@ -104,31 +122,46 @@
   int eventcnt = epoll_wait (backend_fd, epoll_events, epoll_eventmax, (int)ceil (timeout * 1000.));
 
   if (expect_false (eventcnt < 0))
     {
       if (errno != EINTR)
-        syserr ("(libev) epoll_wait");
+        ev_syserr ("(libev) epoll_wait");
 
       return;
     }
 
   for (i = 0; i < eventcnt; ++i)
     {
       struct epoll_event *ev = epoll_events + i;
 
-      int fd   = ev->data.u64;
+      int fd = (uint32_t)ev->data.u64; /* mask out the lower 32 bits */
+      int want = anfds [fd].events;
       int got  = (ev->events & (EPOLLOUT | EPOLLERR | EPOLLHUP) ? EV_WRITE : 0)
                | (ev->events & (EPOLLIN  | EPOLLERR | EPOLLHUP) ? EV_READ  : 0);
-      int want = anfds [fd].events;
 
+      /* check for spurious notification */
+      if (expect_false ((uint32_t)anfds [fd].egen != (uint32_t)(ev->data.u64 >> 32)))
+        {
+          /* recreate kernel state */
+          postfork = 1;
+          continue;
+        }
+
       if (expect_false (got & ~want))
         {
+          anfds [fd].emask = want;
+
           /* we received an event but are not interested in it, try mod or del */
+          /* I don't think we ever need MOD, but let's handle it anyways */
           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);
+          if (epoll_ctl (backend_fd, want ? EPOLL_CTL_MOD : EPOLL_CTL_DEL, fd, ev))
+            {
+              postfork = 1; /* an error occured, recreate kernel state */
+              continue;
+            }
         }
 
       fd_event (EV_A_ fd, got);
     }
 
@@ -153,11 +186,11 @@
 
   backend_fudge  = 0.; /* kernel sources seem to indicate this to be zero */
   backend_modify = epoll_modify;
   backend_poll   = epoll_poll;
 
-  epoll_eventmax = 64; /* intiial number of events receivable per poll */
+  epoll_eventmax = 64; /* initial number of events receivable per poll */
   epoll_events = (struct epoll_event *)ev_malloc (sizeof (struct epoll_event) * epoll_eventmax);
 
   return EVBACKEND_EPOLL;
 }
 
@@ -171,10 +204,10 @@
 epoll_fork (EV_P)
 {
   close (backend_fd);
 
   while ((backend_fd = epoll_create (256)) < 0)
-    syserr ("(libev) epoll_create");
+    ev_syserr ("(libev) epoll_create");
 
   fcntl (backend_fd, F_SETFD, FD_CLOEXEC);
 
   fd_rearm_all (EV_A);
 }