Re: Writing to multiple descriptors with one system call

[Vlad Galu <dudu%dudu.ro@localhost>]

On Thu, Mar 18, 2010 at 1:10 AM, Sad Clouds
<cryintothebluesky%googlemail.com@localhost> wrote:
> On Thu, 18 Mar 2010 00:53:26 +0100
> Jean-Yves Migeon <jeanyves.migeon%free.fr@localhost> wrote:
>
>> On 03/17/10 17:53, Sad Clouds wrote:
>> > 1. Accepting connections
>> >
>> > On busy web server it is likely that the listening socket will have
>> > multiple entries on the completed connection queue (i.e. established
>> > state). You call accept() in a loop until you get EWOULDBLOCK and
>> > since these are new connections, the chances are all these sockets
>> > contain HTTP GET requests for /index.html
>> >
>> > Instead of calling write() 50 times for all 50 new sockets, you
>> > could just call write2v() once.
>>
>> So basically, between the 1st accept(2) and the last, all the clients
>> are waiting for input (which they will get sequentially, when you
>> will perform your write2v() after the _last_ accept(2)).
>>
>> Which means that the 1st "accepted" filedes created will wait for the
>> 50th to be accepted. Seems inefficient for me.
>
> This is what high performance servers do. There is nothing
> "inefficient" about it. You set the listening socket non-blocking and
> call accept() in a loop.

Since you're already worried about context switches, it's better to
watch the accepting file descriptor for read events and block in
kevent().

-- 
Good, fast & cheap. Pick any two.