[PATCH wayland v2] client: Fully flush during blocking dispatch

[Jonas Ådahl]

On Fri, Jan 15, 2016 at 11:43:33AM -0800, Bill Spitzak wrote:
> Would it make sense for wl_display_flush() to do this always? Ie it will
> never return EAGAIN. Then if needed make the non-blocking version be a new
> call.

No, we can't change the semantics of wl_display_flush() to be blocking,
as it is already specified to not be blocking. It'd be an API change.


Jonas

> 
> 
> 
> On Thu, Jan 14, 2016 at 6:40 PM, Jonas Ådahl <jadahl at gmail.com> wrote:
> 
> > On Fri, Jan 15, 2016 at 12:12:09AM +0000, Auke Booij wrote:
> > > On 12 January 2016 at 04:31, Jonas Ådahl <jadahl at gmail.com> wrote:
> > > > wl_display_flush() may fail with EAGAIN which means that not all data
> > > > waiting in the buffer has been flushed. We later block until there
> > >
> > > + is
> >
> > Fixed locally.
> >
> > >
> > > > data to read, which could mean that we block on input from the
> > > > compositor without having sent out all data from the client. Avoid this
> > > > by fully flushing the socket before starting to wait.
> > > >
> > > > Signed-off-by: Jonas Ådahl <jadahl at gmail.com>
> > > > ---
> > > >  src/wayland-client.c | 39 +++++++++++++++++++++++++++++----------
> > > >  1 file changed, 29 insertions(+), 10 deletions(-)
> > > >
> > > > diff --git a/src/wayland-client.c b/src/wayland-client.c
> > > > index 8bf6124..f47e395 100644
> > > > --- a/src/wayland-client.c
> > > > +++ b/src/wayland-client.c
> > > > @@ -1442,6 +1442,21 @@ wl_display_cancel_read(struct wl_display
> > *display)
> > > >         pthread_mutex_unlock(&display->mutex);
> > > >  }
> > > >
> > > > +static int
> > > > +wl_display_poll(struct wl_display *display, short int events)
> > > > +{
> > > > +       int ret;
> > > > +       struct pollfd pfd[2];
> > >
> > > why 2? why an array at all? why not just
> > >
> > > struct pollfd pfd;
> > > pfd.fd = display->fd;
> > > pfd.events = events;
> > > do {
> > >   poll(&pfd, 1, -1);
> > > } while (blabla);
> > >
> > > (i understand this was in the original as well and you're simply
> > > moving code around)
> >
> > The git history doesn't provide an explanation so I guess it is just a
> > mistake. I'll change the 2 to a 1 before pushing.
> >
> >
> > Jonas
> >
> > >
> > > > +
> > > > +       pfd[0].fd = display->fd;
> > > > +       pfd[0].events = events;
> > > > +       do {
> > > > +               ret = poll(pfd, 1, -1);
> > > > +       } while (ret == -1 && errno == EINTR);
> > > > +
> > > > +       return ret;
> > > > +}
> > > > +
> > > >  /** Dispatch events in an event queue
> > > >   *
> > > >   * \param display The display context object
> > > > @@ -1485,27 +1500,31 @@ WL_EXPORT int
> > > >  wl_display_dispatch_queue(struct wl_display *display,
> > > >                           struct wl_event_queue *queue)
> > > >  {
> > > > -       struct pollfd pfd[2];
> > > >         int ret;
> > > >
> > > >         if (wl_display_prepare_read_queue(display, queue) == -1)
> > > >                 return wl_display_dispatch_queue_pending(display,
> > queue);
> > > >
> > > > +       while (true) {
> > > > +               ret = wl_display_flush(display);
> > > > +               if (ret == -1 && errno == EAGAIN) {
> > > > +                       if (wl_display_poll(display, POLLOUT) == -1) {
> > > > +                               wl_display_cancel_read(display);
> > > > +                               return -1;
> > > > +                       }
> > > > +               } else {
> > > > +                       break;
> > > > +               }
> > > > +       }
> > > > +
> > > >         /* Don't stop if flushing hits an EPIPE; continue so we can
> > read any
> > > >          * protocol error that may have triggered it. */
> > > > -       ret = wl_display_flush(display);
> > > > -       if (ret < 0 && errno != EAGAIN && errno != EPIPE) {
> > > > +       if (ret < 0 && errno != EPIPE) {
> > > >                 wl_display_cancel_read(display);
> > > >                 return -1;
> > > >         }
> > > >
> > > > -       pfd[0].fd = display->fd;
> > > > -       pfd[0].events = POLLIN;
> > > > -       do {
> > > > -               ret = poll(pfd, 1, -1);
> > > > -       } while (ret == -1 && errno == EINTR);
> > > > -
> > > > -       if (ret == -1) {
> > > > +       if (wl_display_poll(display, POLLIN) == -1) {
> > > >                 wl_display_cancel_read(display);
> > > >                 return -1;
> > > >         }
> > > > --
> > > > 2.4.3
> > > >
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