The callback will be called when any of the resources requested
from the network failed to load.
There is not recovery implemented yet, so the closest thing to
reseting the Map object and reloading all the resources would
be setting a new style.
We only emit signals when the number of buckets increase (i.e. the
new data that arrived added a new bucket to the tile).
Also, if we try to reparse a partial tile but it is not possible, we
keep the flag up for trying to reparse it again on the next update,
because the data might have arrived after the bucket that is waiting
for the data was processed but before the end of the parsing.
Fixes#1458
When parsing a tile, we request resources from the network, like
sprites and glyphs.
In the rare case of the resources arriving before the tile is
parsed for the first time, if we don't mark it for being parsed
again, it can end up with a tile eternally stuck in the partial
state.
Partial tiles are now only processed again when there is a new resource
available. If we don't have new resources - like new glyphs - the end result
of the reparsing is the same, because no new SymbolBuckets would are created.
In my tests debugging with PowerTOP, this patch drops the CPU utilization
during the sampling period from 100ms/s to 40ms/s. The improvements on
slow connections (i.e. more time waiting for resources) are even more
noticeable.
For now, keep a pointer so we can subscribe/unsubscribe to events. In
the future, we should move this object completely to ResourceLoader, but
we can't do it now because we delete the ResourceLoader when changing
the style.
This still has the unwanted side effect off blocking the Map thread
waiting for the workers to return (because they hold a reference
to the Map thread main loop).
Maybe the only way to solve this would be having a I/O thread for
dispatching messages.
The Request is not bound anymore to the invoker thread because the workers
will request for glyphs, but the reply will arrive at the Map thread.
GlyphStore will notify observers when a glyph range is loaded. By now
the notification is generic, but could be fine grained, causing the
processing of buckets depending on this particular range.
This is the first concrete step to remove promises from the parsing
pipeline. Buckets depending on the Sprite (i.e. SymbolBucket) won't
be created if the Sprite is not loaded yet. When the Sprite finally gets
loaded, it will fire a signal that will ultimately trigger a reparse.
We still have to expose the Sprite to the Map object as it is needed
for getting offset pixels for annotation symbols, but we can probably
improve that.
This pattern, in contrast with callbacks, allows us to clearly see
the dependency and hierarchy between the objects. It will also help
on writing unit tests as we can count how many times a notification
was triggered.
ResourceLoader will handle all the tile changes and notifications
through the Source object owned by the Style. This object lives
entirely on the Map thread and should be only accessed by it.
The observer will receive notifications every time the tile data changes
and this will probably trigger a new rendering operation.
This first patch will delegate Source loading to the ResourceLoader.
