<div dir="ltr"> <div class="gmail_extra"> <div class="gmail_quote">On Wed, Jul 1, 2015 at 10:10 AM, Jonas Ådahl <<a href="mailto:jadahl@gmail.com" target="_blank">jadahl@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class=""><div class="h5">On Wed, Jul 01, 2015 at 09:51:41AM +0200, Marek Chalupa wrote: > On Wed, Jul 1, 2015 at 9:16 AM, Jonas Ådahl <<a href="mailto:jadahl@gmail.com">jadahl@gmail.com</a>> wrote: > > > On Wed, Jul 01, 2015 at 08:57:05AM +0200, Marek Chalupa wrote: > > > On Mon, Jun 29, 2015 at 3:37 PM, Giulio Camuffo <<a href="mailto:giuliocamuffo@gmail.com">giuliocamuffo@gmail.com</a> > > > > > > wrote: > > > > > > > 2015-06-29 14:30 GMT+03:00 Jonas Ådahl <<a href="mailto:jadahl@gmail.com">jadahl@gmail.com</a>>: > > > > > Arnaud Vrac discovered an issue in the libwayland client API causing > > > > > race conditions when doing round trips using the wl_display object > > using > > > > > non-default proxy queues. > > > > > > > > > > The problem is that one thread can read and dispatch events after > > > > > another thread creates the wl_callback object but before it sets the > > > > > queue. This could potentially cause the events to be dropped > > completely > > > > > if the event is dispatched before the creating thread sets the > > > > > implementation, or that the event is dispatched on the wrong queue > > which > > > > > might run on another thread. > > > > > > > > > > This patch introduces API to solve this case by introducing "proxy > > > > > wrappers". In short, a proxy wrapper is a struct wl_proxy * that will > > > > > never itself emit any events, but the client can set a queue, and > > use it > > > > > when sending requests that creates new proxy objects. When sending > > > > > requests, the wrapper will work in the same way as the normal proxy > > > > > object, but the proxy created by sending a request (for example > > > > > wl_display.sync) will default to the same proxy queue as the wrapper. > > > > > > > > > > Signed-off-by: Jonas Ådahl <<a href="mailto:jadahl@gmail.com">jadahl@gmail.com</a>> > > > > > --- > > > > > > > > > > Hi, > > > > > > > > > > This is one of the two alternative solutions that was discussed on > > > > #wayland. > > > > > > > > > > The other one being introducing API alternatives to > > > > > wl_proxy_marshal_constructor and wl_proxy_marshal_array_constructor > > that > > > > > also take a queue and also changing scanner.c to produce functions > > that > > > > > take a queue for every request that creates a proxy. > > > > > > > > > > In short, instead of > > > > > > > > > > bar = wl_foo_get_bar(foo); > > > > > wl_proxy_set_queue((struct wl_proxy *) bar, queue); > > > > > wl_bar_add_listener(bar, ...); > > > > > > > > > > with this RFC a client does > > > > > > > > > > foo_wrapper = wl_proxy_create_wrapper((struct wl_proxy *) > > foo); > > > > > wl_proxy_set_queue((struct wl_proxy *) foo_wrapper, queue); > > > > > > > > > > bar = wl_foo_get(foo_wrapper); > > > > > wl_bar_add_listener(bar, ...); > > > > > > > > > > and the with other idea that is implemented anywhere yet AFAIK > > > > > > > > > > bar = wl_foo_get_bar_with_queue(foo, queue) > > > > > wl_bar_add_listener(bar, ...); > > > > > > > > Hi, i think this second option is better. The proxy approach looks to > > > > me like a clunky and unnecessary workaround, while i don't see > > > > downsides to new api taking a queue. > > > > > > > > I agree that the second approach seems less like a work around, both > > implementation wise and API wise. > > > > However I see one benefit with the first approach that the second lacks > > and that is that one will be able to have code that is unaware of queues > > and dispatching, only doing requests and listening on new objects on > > whatever the default queue happens to be, while the "parent" code is the > > one running the main loop being aware of what thread it is running, > > dispatching on the right queue etc. Not sure it's a use case worth the > > clunkyness how the API would look though. > > > > > > > > > With this second approach there's still a race before setting listener. > > > We should be able to set queue and listener atomically to get rid of this > > > race. > > > > > > So something like: > > > > > > wl_proxy_create_full(..., queue, listener) > > > > > > + the scanner thing? > > > > Since the listener implementation won't be invoked until the events are > > dispatched, and if one sets a separate queue, they won't be dispatched > > until the user dispatches the queue it set. So in that case, there is no > > race as far as I can tell. > > > > > Yes, it works if the queue gets dispatched after setting the listener. > But what if, for example, the client has one thread that is dispatching the > queue > and another that would create proxy with this queue? In this case the > dispatching could > occur before setting the listener, right? </div></div>That is true, but I don't think sharing a queue over multiple threads has been considered a valid use case, i.e. one should have one queue per thread. Or is there something EGL:y that requires it to work? </blockquote><div> </div><div>Hmm, TBH I don't know if creating proxy and assigning it to another's thread queue is valid or not. I know just that dispatching one queue from more threads is considered invalid.</div><div> </div><div>Anyway, I can't find anything about it in docs, so we should probably document it if it is invalid. </div> <blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"> Jonas <div class=""><div class="h5"> > > > > > > Jonas > > > > > > > > > > > > > > > > -- > > > > Giulio > > > > > > > > > > > > > > Opinions? > > > > > > > > > > > > > > > Jonas > > > > > > > > > > > > > > > > > > > > src/wayland-client-core.h | 1 + > > > > > src/wayland-client.c | 106 > > > > +++++++++++++++++++++++++++++++++++++++++----- > > > > > src/wayland-private.h | 7 +++ > > > > > 3 files changed, 103 insertions(+), 11 deletions(-) > > > > > > > > > > diff --git a/src/wayland-client-core.h b/src/wayland-client-core.h > > > > > index dea70d9..0db8b9c 100644 > > > > > --- a/src/wayland-client-core.h > > > > > +++ b/src/wayland-client-core.h > > > > > @@ -125,6 +125,7 @@ void wl_proxy_marshal_array(struct wl_proxy *p, > > > > uint32_t opcode, > > > > > union wl_argument *args); > > > > > struct wl_proxy *wl_proxy_create(struct wl_proxy *factory, > > > > > const struct wl_interface > > *interface); > > > > > +struct wl_proxy *wl_proxy_create_wrapper(struct wl_proxy *proxy); > > > > > struct wl_proxy *wl_proxy_marshal_constructor(struct wl_proxy > > *proxy, > > > > > uint32_t opcode, > > > > > const struct > > wl_interface > > > > *interface, > > > > > diff --git a/src/wayland-client.c b/src/wayland-client.c > > > > > index 6450b67..f8c64c4 100644 > > > > > --- a/src/wayland-client.c > > > > > +++ b/src/wayland-client.c > > > > > @@ -51,7 +51,8 @@ > > > > > > > > > > enum wl_proxy_flag { > > > > > WL_PROXY_FLAG_ID_DELETED = (1 << 0), > > > > > - WL_PROXY_FLAG_DESTROYED = (1 << 1) > > > > > + WL_PROXY_FLAG_DESTROYED = (1 << 1), > > > > > + WL_PROXY_FLAG_WRAPPER = (1 << 2), > > > > > }; > > > > > > > > > > struct wl_proxy { > > > > > @@ -405,17 +406,19 @@ wl_proxy_create_for_id(struct wl_proxy > > *factory, > > > > > void > > > > > proxy_destroy(struct wl_proxy *proxy) > > > > > { > > > > > - if (proxy->flags & WL_PROXY_FLAG_ID_DELETED) > > > > > - wl_map_remove(&proxy->display->objects, proxy-> > > <a href="http://object.id" rel="noreferrer" target="_blank">object.id</a> > > > > ); > > > > > - else if (proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a> < WL_SERVER_ID_START) > > > > > - wl_map_insert_at(&proxy->display->objects, 0, > > > > > - proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>, > > WL_ZOMBIE_OBJECT); > > > > > - else > > > > > - wl_map_insert_at(&proxy->display->objects, 0, > > > > > - proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>, NULL); > > > > > - > > > > > + if (proxy->flags != WL_PROXY_FLAG_WRAPPER) { > > > > > + if (proxy->flags & WL_PROXY_FLAG_ID_DELETED) > > > > > + wl_map_remove(&proxy->display->objects, > > > > > + proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>); > > > > > + else if (proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a> < WL_SERVER_ID_START) > > > > > + wl_map_insert_at(&proxy->display->objects, 0, > > > > > + proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>, > > > > WL_ZOMBIE_OBJECT); > > > > > + else > > > > > + wl_map_insert_at(&proxy->display->objects, 0, > > > > > + proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>, NULL); > > > > > > > > > > - proxy->flags |= WL_PROXY_FLAG_DESTROYED; > > > > > + proxy->flags |= WL_PROXY_FLAG_DESTROYED; > > > > > + } > > > > > > > > > > proxy->refcount--; > > > > > if (!proxy->refcount) > > > > > @@ -459,6 +462,11 @@ WL_EXPORT int > > > > > wl_proxy_add_listener(struct wl_proxy *proxy, > > > > > void (**implementation)(void), void *data) > > > > > { > > > > > + if (proxy->flags == WL_PROXY_FLAG_WRAPPER) { > > > > > + wl_log("proxy %p is a wrapper\n", proxy); > > > > > + return -1; > > > > > + } > > > > > + > > > > > if (proxy->object.implementation || proxy->dispatcher) { > > > > > wl_log("proxy %p already has listener\n", proxy); > > > > > return -1; > > > > > @@ -512,6 +520,11 @@ wl_proxy_add_dispatcher(struct wl_proxy *proxy, > > > > > wl_dispatcher_func_t dispatcher, > > > > > const void *implementation, void *data) > > > > > { > > > > > + if (proxy->flags == WL_PROXY_FLAG_WRAPPER) { > > > > > + wl_log("proxy %p is a wrapper\n", proxy); > > > > > + return -1; > > > > > + } > > > > > + > > > > > if (proxy->object.implementation || proxy->dispatcher) { > > > > > wl_log("proxy %p already has listener\n"); > > > > > return -1; > > > > > @@ -1885,6 +1898,77 @@ wl_proxy_set_queue(struct wl_proxy *proxy, > > struct > > > > wl_event_queue *queue) > > > > > proxy->queue = &proxy->display->default_queue; > > > > > } > > > > > > > > > > +/** Create a proxy wrapper > > > > > + * > > > > > + * \param proxy The proxy object to be wrapped > > > > > + * \return A proxy wrapper for the given proxy > > > > > + * > > > > > + * A proxy wrapper is type of 'struct wl_proxy' instance that can be > > > > used for > > > > > + * sending requests instead of using the original proxy. A proxy > > > > wrapper does > > > > > + * not have an implementation or dispatcher, and events received on > > the > > > > > + * object is still emitted on the original proxy. Trying to set an > > > > > + * implementation or dispatcher will have no effect but result in a > > > > warning > > > > > + * being logged. > > > > > + * > > > > > + * Even though there is no implementation nor dispatcher, the proxy > > > > queue can > > > > > + * be changed. This will affect the default queue of new objects > > > > created by > > > > > + * requests sent via the proxy wrapper. > > > > > + * > > > > > + * A proxy wrapper must be destroyed before the proxy it was created > > > > from. > > > > > + * Creating a proxy wrapper on a proxy that has either been > > destroyed or > > > > > + * removed will fail, and NULL will be returned. > > > > > + * > > > > > + * If a user reads and dispatches events on more than one thread, > > it is > > > > > + * necessary to use a proxy wrapper when sending requests on objects > > > > when the > > > > > + * intention is that a newly created proxy is to use a proxy queue > > > > different > > > > > + * from the proxy the request was sent on, as creating the new proxy > > > > and then > > > > > + * setting the queue is not thread safe. > > > > > + * > > > > > + * For example, a module that runs using its own proxy queue that > > needs > > > > to > > > > > + * do display roundtrip must wrap the wl_display proxy object before > > > > sending > > > > > + * the wl_display.sync request. For example: > > > > > + * > > > > > + * struct wl_proxy *wrapped_display; > > > > > + * struct wl_callback *callback; > > > > > + * > > > > > + * wrapped_display = wl_proxy_create_wrapper((struct wl_proxy *) > > > > display); > > > > > + * callback = wl_display_sync((struct wl_display *) > > wrapped_display); > > > > > + * wl_proxy_destroy(wrapped_display); > > > > > + * wl_callback_add_listener(callback, ...); > > > > > + * > > > > > + * \memberof wl_proxy > > > > > + */ > > > > > +WL_EXPORT struct wl_proxy * > > > > > +wl_proxy_create_wrapper(struct wl_proxy *proxy) > > > > > +{ > > > > > + struct wl_proxy *wrapper; > > > > > + > > > > > + wrapper = zalloc(sizeof *wrapper); > > > > > + if (!wrapper) > > > > > + return NULL; > > > > > + > > > > > + pthread_mutex_lock(&proxy->display->mutex); > > > > > + > > > > > + if ((proxy->flags & WL_PROXY_FLAG_ID_DELETED) || > > > > > + (proxy->flags & WL_PROXY_FLAG_DESTROYED)) { > > > > > + pthread_mutex_unlock(&proxy->display->mutex); > > > > > + wl_log("proxy %p already deleted or destroyed flag: > > > > 0x%x\n", > > > > > + proxy, proxy->flags); > > > > > + return NULL; > > > > > + } > > > > > + > > > > > + wrapper->object.interface = proxy->object.interface; > > > > > + wrapper-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a> = proxy-><a href="http://object.id" rel="noreferrer" target="_blank">object.id</a>; > > > > > + wrapper->display = proxy->display; > > > > > + wrapper->queue = proxy->queue; > > > > > + wrapper->flags = WL_PROXY_FLAG_WRAPPER; > > > > > + wrapper->refcount = 1; > > > > > + > > > > > + pthread_mutex_unlock(&proxy->display->mutex); > > > > > + > > > > > + return wrapper; > > > > > +} > > > > > + > > > > > WL_EXPORT void > > > > > wl_log_set_handler_client(wl_log_func_t handler) > > > > > { > > > > > diff --git a/src/wayland-private.h b/src/wayland-private.h > > > > > index 17c507c..f072811 100644 > > > > > --- a/src/wayland-private.h > > > > > +++ b/src/wayland-private.h > > > > > @@ -29,6 +29,7 @@ > > > > > #define WAYLAND_PRIVATE_H > > > > > > > > > > #include <stdarg.h> > > > > > +#include <stdlib.h> > > > > > > > > > > #define WL_HIDE_DEPRECATED 1 > > > > > > > > > > @@ -71,6 +72,12 @@ struct wl_map { > > > > > > > > > > typedef void (*wl_iterator_func_t)(void *element, void *data); > > > > > > > > > > +static inline void * > > > > > +zalloc(size_t size) > > > > > +{ > > > > > + return calloc(1, size); > > > > > +} > > > > > + > > > > > void wl_map_init(struct wl_map *map, uint32_t side); > > > > > void wl_map_release(struct wl_map *map); > > > > > uint32_t wl_map_insert_new(struct wl_map *map, uint32_t flags, void > > > > *data); > > > > > -- > > > > > 2.1.4 > > > > > > > > > > _______________________________________________ > > > > > wayland-devel mailing list > > > > > <a href="mailto:wayland-devel@lists.freedesktop.org">wayland-devel@lists.freedesktop.org</a> > > > > > <a href="http://lists.freedesktop.org/mailman/listinfo/wayland-devel" rel="noreferrer" target="_blank">http://lists.freedesktop.org/mailman/listinfo/wayland-devel</a> > > > > _______________________________________________ > > > > wayland-devel mailing list > > > > <a href="mailto:wayland-devel@lists.freedesktop.org">wayland-devel@lists.freedesktop.org</a> > > > > <a href="http://lists.freedesktop.org/mailman/listinfo/wayland-devel" rel="noreferrer" target="_blank">http://lists.freedesktop.org/mailman/listinfo/wayland-devel</a> > > > > > > > > > > Regards, > > > Marek > > > > Thanks, > Marek </div></div></blockquote><div> </div><div>Thanks, </div><div>Marek </div></div> </div></div>