This eliminates the reliance on ThreadContext to provide GLObjectStore, and statically enforces that GL cleanup functions happen only when GLObjectStore::performCleanup is called.
With the elimination of the Map thread, this becomes important because there may be multiple GLObjectStore's per-thread, and Map will need to ensure that the correct context is active when calling GLObjectStore::performCleanup.
This adds support for using cached styles that are stale. They're treated like changing styles; when the refreshed style changed compared to the one we've already had, we're swapping out the entire style, which might cause a slight flicker.
* Standardize on std::exception_ptr as the error representation
(fixes#2854).
* Don't format textual strings at the error source; pass on the
constituent data via observer method parameters instead.
* Use the null object pattern to simplify observer notification code.
* Further refactoring for ResourceLoading tests.
The previous fix resulted in annotations sometimes never being added.
This would happen if, during the execution of MapContext::update where
Update::Annotations was set, the style itself was loaded but some of
its subresources (sprite or sources) were not.
#3082 is a follow up issue to make MapContext::update less error-prone.
In MapContext thread, TransformState gets updated from main thread to
MapContext and Painter can safely reference MapContext's TransformState
instead of copying it upon each Painter::render call.
We're now returning stale responses from cache. Those responses will have the `stale` flag set to true. Currently, all requesters in the core code discard stale responses, and cancel the request immediately after they got a non-stale response.
By not automatically destroying Request objects after the result has been delivered, we are making sure that we can potentially fire the callback multiple times without adverse effects. This means that you have to hold on to the result of fs->request(), can explicitly cancel it if you don't want to be notified of data changes anymore. Not doing so will monitor the request indefinitely and will prevent the app from exiting.
