On Wed, 4 May 2016 10:22:35 +0100 Daniel Stone <dan...@fooishbar.org> wrote:
> Hi Jonas, > > On 4 May 2016 at 09:53, Jonas Ådahl <jad...@gmail.com> wrote: > > When EGL is used on some other thread than the thread that drives the > > main wl_display queue, the Wayland EGL dri2 implementation is > > vulnerable to a race condition related to display round trips and global > > object advertisements. > > > > The race that may happen is that after after a proxy is created, but > > before the queue is set, events meant to be emitted via the yet to be > > set queue may already have been queued on the wrong queue. > > > > In order to make it possible to avoid this race, wayland 1.11 > > introduced new API that allows creating a proxy wrapper that may be used > > as the factory proxy when creating new proxies via Wayland requests. The > > queue of a proxy wrapper can be changed without effecting what queue > > events emitted by the actual proxy will be queued on, while still > > effecting what default queue proxies created from it will have. > > This looks good to me, but I am worried about the hard dependency, > both at build and run-time. It would be great to make it optional at > build-time (#ifdef wrapper creation and destruction, just doing a > straight assignment otherwise to allow the other code to not be > #ifdefed), but even better if it could also use dlsym() to discover if > the symbol is available at runtime. Maybe the latter is overkill > though. But wouldn't that need #ifdefs in every place where the wrapper will be used, because if the wrapper is not really the wrapper, there needs to be a call to set the queue? Setting the queue is racy, yes, but it would have a chance of working which it wouldn't have otherwise, right? Potentially breaking also non-threaded apps. Jonas, is this patch missing one more wl_proxy_wrapper_destroy() for the display tear-down? I can only see the destroy in the initialize-failure path. This patch is also fixing an existing leak of wl_dpy in the case the connection was created by the EGL, I think. That should also be mentioned in the commit message. Thanks, pq
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