[sheepdog] [PATCH 1/2] lib: prioritize events for epoll() and enhance event loop

[Liu Yuan]

On 12/20/2012 05:41 PM, Hitoshi Mitake wrote:
> From: Hitoshi Mitake <h.mitake at gmail.com>
> 
> This patch adds two new functionalities to event_loop():
> 1. prioritize registered events
> 2. more flexible control with return values from event handlers
> 
> I'd like to describe the objectives of two functionalities.
> 
> 1. Current event_loop() treats priorities of every registered event
> equally. But in some case, the way of treating them unequally is helpful.
> 
> 2. Previous event handlers returned no values. This patch let them
> return newly defined enum value: event_ret. event_ret has 3 values:
> * EVENT_RET_DONE ... this value means no special actions are required.
>   event loop should continue normally.
> * EVENT_RET_REFRESH ... this value means event_loop() should call
>   epoll_wait() again. If events which should be processed as soon as
>   possible during the event handler, this value is returned. So the
>   event can be processed before already rised events.

I don't get the REFRESH. does it means that the handler knows that some
other events is already queued in the kernel and want to process them as
soon as possible, then goto call epoll_wait() again to retrieve them?

> * EVENT_RET_BREAK ... this value means event_loop() must break
>   immediately.
> 

Better rephrase as EVENT_LOOP_OKAY (event handle is done and continue to
process next event if any), EVENT_LOOP_RETRIEVE(retrieve the new
events), EVENT_LOOP_BREAK(break out the event loop and discard other
events) and do as following:

nr = epoll_wait(efd, polled_events, nr_events, TICK * 1000);
if (nr < 0)
    ...
else if (nr) {
    if (need_sort)
sort:
        sort events...
    for (i = 0; i < nr; i++) {
         ret = ei->handler(ei->fd, e, ei->data);
         switch (ret) {
         case EVENT_LOOP_OKAY:
              break;
         case EVENT_LOOP_RETRIEVE:
              retrieve new events;
              goto sort;
         case EVENT_RET_BREAK:
              goto out;
    }
out:
    ...
}
> +static struct epoll_event *polled_events;
> +static int nr_events;
> +static struct epoll_event **sorted_events;
> +

is it possible to use a single array?

Thanks,
Yuan