[core] Use an actor model for tile worker concurrency

src/mbgl/tile/raster_tile_worker.cpp

@@ -0,0 +1,27 @@
+#include <mbgl/tile/raster_tile_worker.hpp>
+#include <mbgl/tile/raster_tile.hpp>
+#include <mbgl/renderer/raster_bucket.cpp>
+#include <mbgl/actor/actor.hpp>
+
+namespace mbgl {
+
+RasterTileWorker::RasterTileWorker(ActorRef<RasterTileWorker>, ActorRef<RasterTile> parent_)
+    : parent(std::move(parent_)) {
+}
+
+void RasterTileWorker::parse(std::shared_ptr<const std::string> data) {
+    if (!data) {
+        parent.invoke(&RasterTile::onParsed, nullptr); // No data; empty tile.
+        return;
+    }
+
+    try {
+        auto bucket = std::make_unique<RasterBucket>();
+        bucket->setImage(decodeImage(*data));
+        parent.invoke(&RasterTile::onParsed, std::move(bucket));
+    } catch (...) {
+        parent.invoke(&RasterTile::setError, std::current_exception());
+    }
+}
+
+} // namespace mbgl