epoll_wait, epoll_ctl

epoll_wait, epoll_ctl

[Howard Chu]

So, what's supposed to happen in a threaded program where one thread 
does an epoll_ctl on an epoll fd while another thread is currently 
waiting in epoll_wait on the same fd? In particular, what happens if a 
thread does an EPOLL_CTL_DEL on one of the fds that is currently being 
waited on? Is there a possibility of an event being returned on the fd 
even after the EPOLL_CTL_DEL completes?

-- 
  -- Howard Chu
  Chief Architect, Symas Corp.  http://www.symas.com
  Director, Highland Sun        http://highlandsun.com/hyc
  OpenLDAP Core Team            http://www.openldap.org/project/

Re: epoll_wait, epoll_ctl

[Davide Libenzi]

On Fri, 13 Jan 2006, Howard Chu wrote:

> So, what's supposed to happen in a threaded program where one thread does an 
> epoll_ctl on an epoll fd while another thread is currently waiting in 
> epoll_wait on the same fd? In particular, what happens if a thread does an 
> EPOLL_CTL_DEL on one of the fds that is currently being waited on? Is there a 
> possibility of an event being returned on the fd even after the EPOLL_CTL_DEL 
> completes?

The same thing that happens when you close a file on another thread, 
nothing (besides the file being automatically removed from the set). 
Removing a file (either by close or by EPOLL_CTL_DEL) is not an event.



- Davide

RE: epoll_wait, epoll_ctl

[David Schwartz]

> So, what's supposed to happen in a threaded program where one thread
> does an epoll_ctl on an epoll fd while another thread is currently
> waiting in epoll_wait on the same fd?

	Nothing special.

> In particular, what happens if a
> thread does an EPOLL_CTL_DEL on one of the fds that is currently being
> waited on? Is there a possibility of an event being returned on the fd
> even after the EPOLL_CTL_DEL completes?

	Absolutely. The EPOLL_CTL_DEL might not even start until after the event
has been determined to be returned and the wait is in the process of
returning.

	DS