How can the nginx detect the stale event using 'instance'?

[Maxim Dounin]

Hello!

On Tue, Feb 21, 2012 at 06:51:19PM +0900, 김수영 wrote:

> These days, I am studying the nginx source code..
> 
> I think this code is very beautiful, and fully modulized.. BUT so it is difficult to follow the code.-_-;
> 
> BTW, In struct ngx_event_s, there is ‘unsigned instance:1;’..
> 
> I can’t understand how can the nginx detect the stale events using it.-_-;
> 
> Could you please explain the detection mechanism or give me a hint?

The "instance" bit is passed in a event user data to the kernel 
and when the kernel returns the event it's checked against one 
recorded in the event structure.  If there is no match - this 
means the event reported by the kernel is stale (i.e. we've 
already closed the descriptor in the very same event loop 
iteration).

See e.g. src/event/modules/ngx_kqueue_module.c for details, in 
particular ngx_kqueue_set_event() and ngx_kqueue_process_events().

Maxim Dounin