Re: [Qemu-devel] [PATCH 10/10] aio-win32: add support for sockets

[TeLeMan <geleman@gmail.com>]

On Wed, Jul 9, 2014 at 5:53 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Uses the same select/WSAEventSelect scheme as main-loop.c.
> WSAEventSelect() is edge-triggered, so it cannot be used
> directly, but it is still used as a way to exit from a
> blocking g_poll().
>
> Before g_poll() is called, we poll sockets with a non-blocking
> select() to achieve the level-triggered semantics we require:
> if a socket is ready, the g_poll() is made non-blocking too.
>
> Based on a patch from Or Goshen.
>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  aio-win32.c         | 150 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>  block/Makefile.objs |   2 -
>  include/block/aio.h |   2 -
>  3 files changed, 145 insertions(+), 9 deletions(-)
>
> diff --git a/aio-win32.c b/aio-win32.c
> index 4542270..61e3d2d 100644
> --- a/aio-win32.c
> +++ b/aio-win32.c

> @@ -183,6 +318,7 @@ bool aio_poll(AioContext *ctx, bool blocking)
>
>      /* wait until next event */
>      while (count > 0) {
> +        HANDLE event;
>          int ret;
>
>          timeout = blocking
> @@ -196,13 +332,17 @@ bool aio_poll(AioContext *ctx, bool blocking)
>          first = false;
>
>          /* if we have any signaled events, dispatch event */
> -        if ((DWORD) (ret - WAIT_OBJECT_0) >= count) {
> +        event = NULL;
> +        if ((DWORD) (ret - WAIT_OBJECT_0) < count) {
> +            event = events[ret - WAIT_OBJECT_0];
> +        } else if (!have_select_revents) {

when (ret - WAIT_OBJECT_0) >= count and have_select_revents is true,
the following events[ret - WAIT_OBJECT_0] will be overflowed.

>              break;
>          }
>
> +        have_select_revents = false;
>          blocking = false;
>
> -        progress |= aio_dispatch_handlers(ctx, events[ret - WAIT_OBJECT_0]);
> +        progress |= aio_dispatch_handlers(ctx, event);
>
>          /* Try again, but only call each handler once.  */
>          events[ret - WAIT_OBJECT_0] = events[--count];