Re: Unifying epoll,aio,futexes etc. (What I really want from epoll)

[Alan Cox]

On Thu, 2002-10-31 at 22:00, Rusty Russell wrote:
>  try:
> 	for each futex in set {
> 		if (grab in userspace) {
> 			close fds;
> 			return with futex;
> 		}
> 		close old fd for futex if any
> 		call FUTEX_FD to get fd notification of futex;
> 	}
> 
> 	select on fds
> 	set = fds which are ready
> 	goto try
> 
> You could, of course, loop through the fast path once before making any
> syscalls.  Another optimization is to have FUTEX_FD reuse an existing fd
> rather than requiring the close.
> 
> Not sure I get the point about livelock though: deadlock is possible if
> apps seek multiple locks at once without care, of course.

Think about 1000 futexes where one task wants to grab them all and other
tasks want any one of them - done wrongly at that point busy traffic
will starve the 1000 futex waiter.