Every tile parser thread needs its own Style object

[kkaefer]

Style objects are currently shared among several threads. They also modify the style object. #879 addresses some of this by locking StyleBucket objects. Instead, every tile worker should have its own copy of the Style object so that we can't mutate it while the tile parser is currently using it. In addition to that, Style objects should be fully const; right now we're resolving parse time constants depending on the current tile's zoom level and change the Style object.

[ljbade]

Not sure if this was fixed already but being able to load/save the style's state without waiting for the style JSON to load is needed for Android to restore state when a backgrounded application is terminated then restarted in the foreground.

[kkaefer]

Nope, we're currently parsing the Style object in the UI thread, unless it's loaded via HTTP. This is a different issue though and captured in #883.

[incanus]

@kkaefer How critical do you think this is? Is this something that we can push from the iOS beta milestone? What is the practical possibility of multi-threaded mutation right now?

[kkaefer]

Not critical for Beta. There are a few other patches (cf235c6, e00bae4, c30bb1a, e8389d8, 0151fe6) in master that alleviate most of this.

[kkaefer]

This is no longer an issue.