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

[Derek Foreman]

On 11/01/16 10:31 PM, Jonas Ådahl 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
> 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.

Is this because wl_connection_flush() uses sendmsg with MSG_DONTWAIT?

Can we figure out a way to get "bool blocking" down to
wl_connection_flush and avoid the poll thing entirely?  Maybe have a
wl_display_blocking_flush() or whatever...

Wouldn't even need to be external API if only wl_display_dispatch_queue
calls it...

Thanks,
Derek

> 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];
> +
> +	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;
>  	}
>