[ViewVC] Diff of: cvs/libev/ev

Comparing libev/ev_linuxaio.c (file contents):
Revision 1.12 by root, Sun Jun 23 23:02:09 2019 UTC vs.
Revision 1.14 by root, Sun Jun 23 23:49:56 2019 UTC

 static int
 linuxaio_get_events_from_ring (EV_P)
 {
   struct aio_ring *ring = (struct aio_ring *)linuxaio_ctx;
-  unsigned head = ring->head;
+  /* the kernel reads and writes both of these variables, */
+  /* as a C extension, we assume that volatile use here */
+  /* both makes reads atomic and once-only */
+  unsigned head = *(volatile unsigned *)&ring->head;
   unsigned tail = *(volatile unsigned *)&ring->tail;
   if (head == tail)
     return 0;
     {
       linuxaio_parse_events (EV_A_ ring->io_events + head, ring->nr - head);
       linuxaio_parse_events (EV_A_ ring->io_events, tail);
     }
+  /* as an extension to C, we hope that the volatile will makethis atomic and once-only */
   *(volatile unsigned *)&ring->head = tail;
   /* make sure kernel can see our new head value - probably not required */
   ECB_MEMORY_FENCE_RELEASE;
   return 1;
       return 0;
     }
   ev_io_init  (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
   ev_io_start (EV_A_ &linuxaio_epoll_w);
+  ev_unref (EV_A); /* watcher should not keep loop alive */
 #endif
   backend_modify  = linuxaio_modify;
   backend_poll    = linuxaio_poll;
    ev_syserr ("(libev) linuxaio epoll_create");
   ev_io_stop  (EV_A_ &linuxaio_epoll_w);
   ev_io_init  (EV_A_ &linuxaio_epoll_w, linuxaio_epoll_cb, backend_fd, EV_READ);
   ev_io_start (EV_A_ &linuxaio_epoll_w);
-  ev_unref (EV_A); /* watcher should not keep loop alive */
 #endif
   fd_rearm_all (EV_A);
 }

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