[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`.

2 files changed, 10 insertions, 14 deletions

diff --git a/benchmark/api/query.benchmark.cpp b/benchmark/api/query.benchmark.cpp
index 9b7c2d7273..7f08da73d0 100644
--- a/benchmark/api/query.benchmark.cpp
+++ b/benchmark/api/query.benchmark.cpp
@@ -3,7 +3,6 @@
 #include <mbgl/map/map.hpp>
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/renderer/renderer.hpp>
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/image.hpp>
@@ -30,9 +29,8 @@ public:
     }
 
     util::RunLoop loop;
-    ThreadPool threadPool{ 4 };
-    HeadlessFrontend frontend { { 1000, 1000 }, 1, threadPool };
-    Map map { frontend, MapObserver::nullObserver(), threadPool,
+    HeadlessFrontend frontend { { 1000, 1000 }, 1 };
+    Map map { frontend, MapObserver::nullObserver(),
               MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()),
               ResourceOptions().withCachePath("benchmark/fixtures/api/cache.db").withAssetPath(".").withAccessToken("foobar") };
     ScreenBox box{{ 0, 0 }, { 1000, 1000 }};
diff --git a/benchmark/api/render.benchmark.cpp b/benchmark/api/render.benchmark.cpp
index 3cff0d9056..f9d3911f0b 100644
--- a/benchmark/api/render.benchmark.cpp
+++ b/benchmark/api/render.benchmark.cpp
@@ -4,7 +4,6 @@
 #include <mbgl/map/map_observer.hpp>
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/renderer/renderer.hpp>
 #include <mbgl/style/style.hpp>
 #include <mbgl/style/image.hpp>
@@ -29,7 +28,6 @@ public:
     }
 
     util::RunLoop loop;
-    ThreadPool threadPool { 4 };
 };
 
 static void prepare(Map& map, optional<std::string> json = {}) {
@@ -44,8 +42,8 @@ static void prepare(Map& map, optional<std::string> json = {}) {
 
 static void API_renderStill_reuse_map(::benchmark::State& state) {
     RenderBenchmark bench;
-    HeadlessFrontend frontend { size, pixelRatio, bench.threadPool };
-    Map map { frontend, MapObserver::nullObserver(), bench.threadPool,
+    HeadlessFrontend frontend { size, pixelRatio };
+    Map map { frontend, MapObserver::nullObserver(),
               MapOptions().withMapMode(MapMode::Static).withSize(size).withPixelRatio(pixelRatio),
               ResourceOptions().withCachePath(cachePath).withAccessToken("foobar") };
     prepare(map);
@@ -57,8 +55,8 @@ static void API_renderStill_reuse_map(::benchmark::State& state) {
 
 static void API_renderStill_reuse_map_formatted_labels(::benchmark::State& state) {
     RenderBenchmark bench;
-    HeadlessFrontend frontend { size, pixelRatio, bench.threadPool };
-    Map map { frontend, MapObserver::nullObserver(), bench.threadPool,
+    HeadlessFrontend frontend { size, pixelRatio };
+    Map map { frontend, MapObserver::nullObserver(),
               MapOptions().withMapMode(MapMode::Static).withSize(size).withPixelRatio(pixelRatio),
               ResourceOptions().withCachePath(cachePath).withAccessToken("foobar") };
     prepare(map, util::read_file("benchmark/fixtures/api/style_formatted_labels.json"));
@@ -70,8 +68,8 @@ static void API_renderStill_reuse_map_formatted_labels(::benchmark::State& state
 
 static void API_renderStill_reuse_map_switch_styles(::benchmark::State& state) {
     RenderBenchmark bench;
-    HeadlessFrontend frontend { size, pixelRatio, bench.threadPool };
-    Map map { frontend, MapObserver::nullObserver(), bench.threadPool,
+    HeadlessFrontend frontend { size, pixelRatio };
+    Map map { frontend, MapObserver::nullObserver(),
               MapOptions().withMapMode(MapMode::Static).withSize(size).withPixelRatio(pixelRatio),
               ResourceOptions().withCachePath(cachePath).withAccessToken("foobar") };
 
@@ -87,8 +85,8 @@ static void API_renderStill_recreate_map(::benchmark::State& state) {
     RenderBenchmark bench;
 
     while (state.KeepRunning()) {
-        HeadlessFrontend frontend { size, pixelRatio, bench.threadPool };
-        Map map { frontend, MapObserver::nullObserver(), bench.threadPool,
+        HeadlessFrontend frontend { size, pixelRatio };
+        Map map { frontend, MapObserver::nullObserver(),
                   MapOptions().withMapMode(MapMode::Static).withSize(size).withPixelRatio(pixelRatio),
                   ResourceOptions().withCachePath(cachePath).withAccessToken("foobar") };
         prepare(map);