[PATCH wayland] server: add helper functions for wl_global

[Bryce Harrington]

On Mon, Mar 09, 2015 at 09:49:19AM +0200, Pekka Paalanen wrote:
> On Mon, 23 Feb 2015 17:20:37 -0800
> Bryce Harrington <bryce at osg.samsung.com> wrote:
> 
> > On Mon, Feb 23, 2015 at 11:30:57AM -0800, Bill Spitzak wrote:
> > > Which of the 4 arguments do you use for your use case?
> > > 
> > > Because this can only return the first match I suspect some of the
> > > NULL tests are pretty useless, because you have to specify arguments
> > > that you know will return the one and only instance you are
> > > interested in. It might be better to make this exactly match the use
> > > case you have. If you are passing NULL just remove that argument,
> > > and conversely remove the null test from this code for the arguments
> > > you send. Basically don't add code that is not certain to be useful.
> > 
> > I would assume he's using all of them.
> > 
> > Regardless, so long as the test case covers an adequate number of
> > permutations I don't see an issue with providing a generalized solution
> > to this need.
> > 
> > However, I suspect this API would be better named as
> > wl_global_find_first().
> > 
> > A more general wl_global_find() I would expect to be returning a list of
> > results.

Lacking some sort of 'yield' like mechanism, wouldn't returning a list
incur performance impacts?

> > One thing to think about when writing a test case, is if this function
> > will always return the same first result.  E.g. if the globals list
> > depends at all on timing of hardware bringup thight might vary boot to
> > boot, or if hashes are in any way involved in creating it, or etc.
> > I'm guessing that's not the case, but probably worth checking, else
> > we'll inevitably have a bug reported about it on some obscure piece of
> > hardware.
> 
> Hi,
> 
> I'm certainly in favour of making this "find" API to return *all*
> matches, not just a random match like it is now. Then, if the caller
> expects to ever find either 0 or 1 globals, it can yell if that
> invariant is ever broken.
> 
> But, I also cannot really see why the underlying problem could not be
> solved completely inside the libEGL implementation.
> 
> If one is looking for an existing wl_drm global, you already assume it
> has been created by *this* particular libEGL where you are currently
> executing. Therefore, this loaded libEGL.so could maintain
> library-global state where it lists the wl_drm globals it has created
> and for which wl_display.
> 
> But, I also imagine that might be more complicated to realize than
> using a find-API, so the idea of the find API is ok by me.
> 
> I would just want it to return all hits. That way you don't even need
> to special-case the no-parameters case and you just trivially return
> all globals.
> 
> Btw. just to be annoying... ;-)
> Does EGL spec say anything about multi-threaded calls into the EGL API?
> How do you know which lock protects the libEGL's globals? Is there only
> one global lock for everything that would guarantee the list returned
> by the find-API won't become out-of-date?
> 
> 
> Thanks,
> pq
> 
> 
> > > On 02/23/2015 10:06 AM, Jonny Lamb wrote:
> > > 
> > > >+/** Find a wl_global given search parameters
> > > >+ *
> > > >+ * \param display The display object
> > > >+ * \param interface The interface to match, or NULL
> > > >+ * \param version The version to match, or 0
> > > >+ * \param data The user data to match, or NULL
> > > >+ * \param bind The function used to bind the object, or NULL
> > > >+ * \return The first wl_global which matches, or NULL
> > > >+ *
> > > >+ * The global list of a wl_display is not public so this function helps in
> > > >+ * finding a specific wl_global based on the parameters. Parameters can be
> > > >+ * missing for a broader search (NULL for interface, data, and bind, and 0 for
> > > >+ * version) but at least one must be present or no result will be returned.
> > > >+ *
> > > >+ * \memberof wl_global
> > > >+ */
> > > >+WL_EXPORT struct wl_global *
> > > >+wl_global_find(struct wl_display *display,
> > > >+	const struct wl_interface *interface, uint32_t version,
> > > >+	void *data, wl_global_bind_func_t bind)
> > > _______________________________________________
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