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



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.

> ---
>  src/rpc/virnetclient.c |   35 +++++++++++++++++++++++++++++++----
>  1 file changed, 31 insertions(+), 4 deletions(-)
> 
> diff --git a/src/rpc/virnetclient.c b/src/rpc/virnetclient.c
> index c62e045..3e661d2 100644
> --- a/src/rpc/virnetclient.c
> +++ b/src/rpc/virnetclient.c
> @@ -1470,12 +1470,30 @@ error:
>  }
>  
>  
> +static bool
> +virNetClientIOUpdateEvents(virNetClientCallPtr call,
> +                           void *opaque)
> +{
> +    int *events = opaque;
> +
> +    if (call->mode == VIR_NET_CLIENT_MODE_WAIT_TX)
> +        *events |= VIR_EVENT_HANDLE_WRITABLE;
> +
> +    return false;
> +}
> +
> +
>  static void virNetClientIOUpdateCallback(virNetClientPtr client,
>                                           bool enableCallback)
>  {
>      int events = 0;
> -    if (enableCallback)
> +
> +    if (enableCallback) {
>          events |= VIR_EVENT_HANDLE_READABLE;
> +        virNetClientCallMatchPredicate(client->waitDispatch,
> +                                       virNetClientIOUpdateEvents,
> +                                       &events);
> +    }
>  
>      virNetSocketUpdateIOCallback(client->sock, events);
>  }
> @@ -1670,11 +1688,20 @@ void virNetClientIncomingEvent(virNetSocketPtr sock,
>          goto done;
>      }
>  
> -    if (virNetClientIOHandleInput(client) < 0) {
> -        VIR_WARN("Something went wrong during async message processing");
> -        virNetSocketRemoveIOCallback(sock);
> +    if (events & VIR_EVENT_HANDLE_WRITABLE) {
> +        if (virNetClientIOHandleOutput(client) < 0)
> +            virNetSocketRemoveIOCallback(sock);
> +    }
> +
> +    if (events & VIR_EVENT_HANDLE_READABLE) {
> +        if (virNetClientIOHandleInput(client) < 0)
> +            virNetSocketRemoveIOCallback(sock);
>      }
>  
> +    /* Remove completed calls or signal their threads. */
> +    virNetClientCallRemovePredicate(&client->waitDispatch,
> +                                    virNetClientIOEventLoopRemoveDone,
> +                                    NULL);
>  done:
>      virNetClientUnlock(client);
>  }

ACK,  I always thought we should be doing this :-)


Daniel
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