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Re: [libvirt] [PATCH 02/12] client rpc: Use event loop for writing



On Wed, Jun 13, 2012 at 10:50:09AM +0200, Jiri Denemark wrote:
> On Wed, Jun 13, 2012 at 09:43:54 +0100, Daniel P. Berrange wrote:
> > On Wed, Jun 13, 2012 at 10:40:48AM +0200, Jiri Denemark wrote:
> > > On Wed, Jun 13, 2012 at 09:30:30 +0100, Daniel P. Berrange wrote:
> > > > On Wed, Jun 13, 2012 at 01:29:20AM +0200, Jiri Denemark wrote:
> > > > > Normally, when every call has a thread associated with it, the thread
> > > > > may get the buck and be in charge of sending all calls until its own
> > > > > call is done. When we introduced non-blocking calls, we had to add
> > > > > special handling of new non-blocking calls. This patch uses event loop
> > > > > to send data if there is no thread to get the buck so that any
> > > > > non-blocking calls left in the queue are properly sent without having to
> > > > > handle them specially. It also avoids adding even more cruft to client
> > > > > IO loop in the following patches.
> > > > > 
> > > > > With this change in, non-blocking calls may see unpredictable delays in
> > > > > delivery when the client has no event loop registered. However, the only
> > > > > non-blocking calls we have are keepalives and we already require event
> > > > > loop for them.
> > > > 
> > > > Is that 'see unpredictable delays' part really correct. AFAIK, there
> > > > should be a pretty well defined "delay" - it'll be processed on the very
> > > > next iteration of the event - assuming the socket is writable. I don't
> > > > really thing this is a delay at all in fact.
> > > 
> > > OK, it's unpredictable but in the case of keepalive calls the delay is at most
> > > keepalive interval. The call may be processed earlier if a libvirt API is
> > > called in the meantime. I'll reword it a bit.
> > 
> > Doesn't the fact that we use the event loop for writing mean that we
> > are not needing to wait for a libvirt API to be called any more ?
> 
> Yes, but the last paragraph was specifically talking about the case when the
> client has no event loop registered, which we still need to support for
> backward compatibility. However, as already said, we require event loop for
> keepalive and keepalive calls are the only non-blocking calls we have. Thus it
> was just a note for the future if someone ever introduces another type of
> non-blocking calls.


Ahhhh, I see. It wasn't clear that you were refering to the no-eventloop
case.

Daniel
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