On Sun, 4 Jul 1999, Peter Wemm wrote:

> "Brian F. Feldman" wrote:
> > On Fri, 2 Jul 1999, Jonathan Lemon wrote:
> > 
> > > In article <local.mail.freebsd-hackers/Pine.LNX.3.95.990702160538.27513C-10
>     [EMAIL PROTECTED]> you write:
> > > >now supports the select() and poll() system calls.  My question is really 
>     one
> > > >of usage.  Why would one us poll() over select()?  Is select eventually go
>     ing
> > > >to go away for some reason?  
> > > 
> > > select() as a user-level call will never go away; there is a large base
> > > of code that uses it.
> > > 
> > > poll() is faster (it doesn't have to do bit twiddling), and it's interface
> > > is cleaner (it can report invalid fd's, something select() can't do).  As
> > > its functionality is a superset of select()'s, it is used as the internal
> > > implementation for select().
> > 
> > Actually, select() doesn't require horrendous amounts of copyin()s, which
> > poll() does. So have you benchmarked the two? I'd expect select to be faster.
> 
> Actually.. select() has three copyins and three copyouts per call.  poll()
> has one copyin and one copyout per call.
> 

But poll() copies in HUGE amounts of data compared to the few bytes for
thousands of FDs that select does.

> Now what I particular like is the event queue system that David Filo put
> together for Yahoo. In a nutshell you create a queue (a fd), and then
> register the descriptors you want to monitor with the queue.  You then run
> an accept()-like loop where the accept returns the fd number that has met
> the conditions you asked for.  For example, if you wanted to know if fd
> number 4251 becomes readable, then the accept would return 4251. This has
> potential to work across multiple processes sharing a queue so that events
> could get round robined or whatever.  The other good part is that it
> maintains the state and lists persistantly and doesn't have to keep copying
> it to/from the kernel.  It handles 50,000 to 100,000 connections without
> too much trouble.  You can still use this with select as the queue fd
> becomes readable when there is an event waiting for your process.
> 
> Is there interest in doing something like this in general?

Yes! That would not replace select() or poll(), but it would be awesome
to have!

> 
> Cheers,
> -Peter
> --
> Peter Wemm - [EMAIL PROTECTED]; [EMAIL PROTECTED]; [EMAIL PROTECTED]
> 
> 
> 
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