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Date: Fri, 04 May 2012 21:49:47 +0200
From: Stefan Weil <sw@weilnetz.de>
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Subject: Re: [Qemu-devel] [PATCH] sdl: Avoid unnecessary resizing of the
 display surface
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To: Anthony Liguori <aliguori@us.ibm.com>
Cc: qemu-devel@nongnu.org

Am 01.05.2012 07:53, schrieb Stefan Weil:
> If neither width nor height changes, nothing has to be done.
>
> Cc: Anthony Liguori<aliguori@us.ibm.com>
> Signed-off-by: Stefan Weil<sw@weilnetz.de>
> ---
>
> This patch improves SDL for any host (for example with remote X displays),
> but the main reason why I wrote it was another problem:
>
> On w32 / w64 hosts, qemu-system-arm has a deadlock when it calls
> sdl_resize_displaysurface during Linux boot. One thread waits for
> a critical region, another thread waits inside SDL_SetVideoMode.
>
> The patch avoids this problem. Paolo, maybe you have an idea what
> could cause the deadlock. Debugging on wxx is terrible - up to now,
> I did not succeed in analysing the lock situation with gdb.
>
> Regards,
> Stefan W.
>
>   ui/sdl.c |    7 +++++--
>   1 files changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/ui/sdl.c b/ui/sdl.c
> index 8700b7a..8c1c71c 100644
> --- a/ui/sdl.c
> +++ b/ui/sdl.c
> @@ -224,8 +224,11 @@ static void sdl_free_displaysurface(DisplaySurface *surface)
>
>   static DisplaySurface* sdl_resize_displaysurface(DisplaySurface *surface, int width, int height)
>   {
> -    sdl_free_displaysurface(surface);
> -    return sdl_create_displaysurface(width, height);
> +    if (surface->width != width || surface->height != height) {
> +        sdl_free_displaysurface(surface);
> +        surface = sdl_create_displaysurface(width, height);
> +    }
> +    return surface;
>   }
>
>   /* generic keyboard conversion */
>    

Please don't apply this patch. It is not complete and can cause a
crash (seen on w32 when resizing the SDL window).

I'll send an update.

Regards,
Stefan W.