[Development] epoll event dispatcher

[Thiago Macieira]

On quinta-feira, 8 de agosto de 2013 17:46:05, Oswald Buddenhagen wrote:
> epoll() perfectly fits the design of an object-oriented notifier
> interface as we have. why does qt code toggle the notifiers so often?
> would it be possible to rewrite it?

Not sure. There is some code that does it because Windows requires toggling, 
so it does so in all platforms (because it's cheap, as it doesn't require a 
syscall to do so). The code is also based on buffers and how often the user 
code empties those buffers. So it will be affected by user code too.

But even if I'm wrong, I'd like to do what you're asking for here:

> would it be possible to optimize it
> behind the scenes (e.g., propagate the toggling to the kernel only upon
> entering the event loop)?

Yes, that would be ideal. That would require iterating over all socket 
notifiers we have on this event dispatcher, to determine which ones have 
changed since. Then we'd have to do a series of epoll_ctl calls to toggle 
before doing our sleep with epoll_wait.

I'd rather not do a flurry of syscalls before epoll_wait. That's wasteful. 
Instead, I'd rather have a syscall that sets the file descriptor state and 
sleeps in one single syscall.

That's called poll(2).

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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