code review 4275042: net: don't loop to drain wakeup pipe.

net: don't loop to drain wakeup pipe.

The loop always makes an extra system call.  It only makes a
difference if more than 100 goroutines started waiting for
something to happen on a network file descriptor since the
last time the pipe was drained, which is unlikely since we
will be woken up the first time a goroutine starts waiting.
If we don't drain the pipe this time, we'll be woken up again
right away and can drain again.

[iant, 2011-03-12 01:26:06]

Hello rsc (cc: golang-dev@googlegroups.com),

I'd like you to review this change to
https://go.googlecode.com/hg/

[rsc, 2011-03-12 01:47:51]

LGTM

I have been meaning to find out whether you can add events
to a kqueue/epoll/whatever while another thread is sleeping on it.
That would eliminate the whole dance.

Russ

[iant, 2011-03-12 02:01:34]

*** Submitted as http://code.google.com/p/go/source/detail?r=6b93721889f3 ***

net: don't loop to drain wakeup pipe.

The loop always makes an extra system call.  It only makes a
difference if more than 100 goroutines started waiting for
something to happen on a network file descriptor since the
last time the pipe was drained, which is unlikely since we
will be woken up the first time a goroutine starts waiting.
If we don't drain the pipe this time, we'll be woken up again
right away and can drain again.

R=rsc
CC=golang-dev
http://codereview.appspot.com/4275042

[bradfitzgoog, 2011-03-12 02:04:47]

For epoll the answer is yes.

(phone), brad
On Mar 11, 2011 5:48 PM, "Russ Cox" <rsc@golang.org> wrote:
> LGTM
>
> I have been meaning to find out whether you can add events
> to a kqueue/epoll/whatever while another thread is sleeping on it.
> That would eliminate the whole dance.
>
> Russ

[dave_cheney.net, 2011-03-12 03:47:06]

I believe that is also true for kqueue. 

Sent from my iPad

On 12/03/2011, at 13:04, Brad Fitzpatrick <bradfitz@google.com> wrote:

> For epoll the answer is yes.
> 
> (phone), brad
> 
> On Mar 11, 2011 5:48 PM, "Russ Cox" <rsc@golang.org> wrote:
> > LGTM
> > 
> > I have been meaning to find out whether you can add events
> > to a kqueue/epoll/whatever while another thread is sleeping on it.
> > That would eliminate the whole dance.
> > 
> > Russ