[core] Make the BackgroundScheduler a singleton

- Do not carry it over everywhere as parameter, it is a shared
  instance anyway and the lifecycle is pretty much the app lifecycle
  from the moment we instantiate a map.
- Rename to BackgroundScheduler because it is a Scheduler that will
  do tasks in the background, we don't make assumptions if it is a
  thread pool or a single thread.
- Most importantly, remove the dependency from `core` on `platform`.

6 files changed, 12 insertions, 25 deletions

diff --git a/test/api/annotations.test.cpp b/test/api/annotations.test.cpp
index 11920d1624..2d76a3d154 100644
--- a/test/api/annotations.test.cpp
+++ b/test/api/annotations.test.cpp
@@ -2,7 +2,6 @@
 #include <mbgl/test/stub_file_source.hpp>
 #include <mbgl/test/map_adapter.hpp>
 
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/annotation/annotation.hpp>
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/image.hpp>
@@ -28,10 +27,9 @@ std::unique_ptr<style::Image> namedMarker(const std::string& name) {
 class AnnotationTest {
 public:
     util::RunLoop loop;
-    ThreadPool threadPool { 4 };
-    HeadlessFrontend frontend { 1, threadPool };
+    HeadlessFrontend frontend { 1 };
 
-    MapAdapter map { frontend, MapObserver::nullObserver(), std::make_shared<StubFileSource>(), threadPool,
+    MapAdapter map { frontend, MapObserver::nullObserver(), std::make_shared<StubFileSource>(),
                   MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize())};
 
     void checkRendering(const char * name) {
diff --git a/test/api/api_misuse.test.cpp b/test/api/api_misuse.test.cpp
index b65bdf9918..54d8eb5912 100644
--- a/test/api/api_misuse.test.cpp
+++ b/test/api/api_misuse.test.cpp
@@ -6,7 +6,6 @@
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/gfx/backend_scope.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/util/exception.hpp>
 #include <mbgl/util/run_loop.hpp>
 
@@ -21,11 +20,10 @@ TEST(API, RenderWithoutCallback) {
 
     util::RunLoop loop;
 
-    ThreadPool threadPool(4);
-    HeadlessFrontend frontend { 1, threadPool };
+    HeadlessFrontend frontend { 1 };
 
     auto map = std::make_unique<MapAdapter>(frontend, MapObserver::nullObserver(),
-                                            std::make_shared<StubFileSource>(), threadPool,
+                                            std::make_shared<StubFileSource>(),
                                             MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()));
     map->renderStill(nullptr);
 
diff --git a/test/api/custom_geometry_source.test.cpp b/test/api/custom_geometry_source.test.cpp
index f796e3086b..df65dc2703 100644
--- a/test/api/custom_geometry_source.test.cpp
+++ b/test/api/custom_geometry_source.test.cpp
@@ -2,7 +2,6 @@
 
 #include <mbgl/map/map.hpp>
 #include <mbgl/map/map_options.hpp>
-#include <mbgl/util/shared_thread_pool.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
 #include <mbgl/storage/resource_options.hpp>
 #include <mbgl/style/style.hpp>
@@ -20,9 +19,8 @@ using namespace mbgl::style;
 TEST(CustomGeometrySource, Grid) {
     util::RunLoop loop;
 
-    auto threadPool = sharedThreadPool();
-    HeadlessFrontend frontend { 1, *threadPool };
-    Map map(frontend, MapObserver::nullObserver(), *threadPool,
+    HeadlessFrontend frontend { 1 };
+    Map map(frontend, MapObserver::nullObserver(),
             MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()),
             ResourceOptions().withCachePath(":memory:").withAssetPath("test/fixtures/api/assets"));
     map.getStyle().loadJSON(util::read_file("test/fixtures/api/water.json"));
diff --git a/test/api/custom_layer.test.cpp b/test/api/custom_layer.test.cpp
index 4a0a34bafc..e9b9aee9bc 100644
--- a/test/api/custom_layer.test.cpp
+++ b/test/api/custom_layer.test.cpp
@@ -3,7 +3,6 @@
 #include <mbgl/platform/gl_functions.hpp>
 #include <mbgl/map/map.hpp>
 #include <mbgl/map/map_options.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/gl/defines.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
 #include <mbgl/storage/resource_options.hpp>
@@ -90,9 +89,8 @@ public:
 TEST(CustomLayer, Basic) {
     util::RunLoop loop;
 
-    ThreadPool threadPool(4);
-    HeadlessFrontend frontend { 1, threadPool };
-    Map map(frontend, MapObserver::nullObserver(), threadPool,
+    HeadlessFrontend frontend { 1 };
+    Map map(frontend, MapObserver::nullObserver(),
             MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()),
             ResourceOptions().withCachePath(":memory:").withAssetPath("test/fixtures/api/assets"));
     map.getStyle().loadJSON(util::read_file("test/fixtures/api/water.json"));
diff --git a/test/api/query.test.cpp b/test/api/query.test.cpp
index ddf5df6aab..b80d3b7d8a 100644
--- a/test/api/query.test.cpp
+++ b/test/api/query.test.cpp
@@ -1,7 +1,6 @@
 #include <mbgl/test/map_adapter.hpp>
 
 #include <mbgl/map/map_options.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/test/stub_file_source.hpp>
 #include <mbgl/test/util.hpp>
 #include <mbgl/util/image.hpp>
@@ -35,9 +34,8 @@ public:
 
     util::RunLoop loop;
     std::shared_ptr<StubFileSource> fileSource = std::make_shared<StubFileSource>();
-    ThreadPool threadPool { 4 };
-    HeadlessFrontend frontend { 1, threadPool };
-    MapAdapter map { frontend, MapObserver::nullObserver(), fileSource, threadPool,
+    HeadlessFrontend frontend { 1 };
+    MapAdapter map { frontend, MapObserver::nullObserver(), fileSource,
                   MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize())};
 };
 
diff --git a/test/api/recycle_map.cpp b/test/api/recycle_map.cpp
index 18cc9c00aa..55e19e3cd9 100644
--- a/test/api/recycle_map.cpp
+++ b/test/api/recycle_map.cpp
@@ -9,7 +9,6 @@
 #include <mbgl/style/sources/geojson_source.hpp>
 #include <mbgl/style/image.hpp>
 #include <mbgl/style/style.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/util/exception.hpp>
 #include <mbgl/util/geometry.hpp>
 #include <mbgl/util/geojson.hpp>
@@ -23,11 +22,9 @@ using namespace mbgl::style;
 TEST(API, RecycleMapUpdateImages) {
     util::RunLoop loop;
 
-    ThreadPool threadPool(4);
-
-    HeadlessFrontend frontend { 1, threadPool };
+    HeadlessFrontend frontend { 1 };
     auto map = std::make_unique<MapAdapter>(frontend, MapObserver::nullObserver(),
-                                         std::make_shared<StubFileSource>(), threadPool,
+                                         std::make_shared<StubFileSource>(),
                                          MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()));
 
     EXPECT_TRUE(map);