[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`.

3 files changed, 21 insertions, 23 deletions

diff --git a/test/util/async_task.test.cpp b/test/util/async_task.test.cpp
index f3025e8952..682926a17d 100644
--- a/test/util/async_task.test.cpp
+++ b/test/util/async_task.test.cpp
@@ -1,14 +1,15 @@
 #include <mbgl/util/async_task.hpp>
-#include <mbgl/util/run_loop.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
-#include <mbgl/actor/actor_ref.hpp>
 
+#include <mbgl/actor/actor_ref.hpp>
+#include <mbgl/actor/scheduler.hpp>
 #include <mbgl/test/util.hpp>
+#include <mbgl/util/run_loop.hpp>
 
 #include <atomic>
 #include <future>
 #include <vector>
 
+using namespace mbgl;
 using namespace mbgl::util;
 
 namespace {
@@ -104,11 +105,11 @@ TEST(AsyncTask, RequestCoalescingMultithreaded) {
     unsigned count = 0, numThreads = 25;
     AsyncTask async([&count] { ++count; });
 
-    mbgl::ThreadPool threads(numThreads);
-    auto mailbox = std::make_shared<mbgl::Mailbox>(threads);
+    auto retainer = Scheduler::GetBackground();
+    auto mailbox = std::make_shared<Mailbox>(*retainer);
 
     TestWorker worker(&async);
-    mbgl::ActorRef<TestWorker> workerRef(worker, mailbox);
+    ActorRef<TestWorker> workerRef(worker, mailbox);
 
     for (unsigned i = 0; i < numThreads; ++i) {
         workerRef.invoke(&TestWorker::run);
@@ -133,11 +134,11 @@ TEST(AsyncTask, ThreadSafety) {
 
     AsyncTask async([&count] { ++count; });
 
-    mbgl::ThreadPool threads(numThreads);
-    auto mailbox = std::make_shared<mbgl::Mailbox>(threads);
+    auto retainer = Scheduler::GetBackground();
+    auto mailbox = std::make_shared<Mailbox>(*retainer);
 
     TestWorker worker(&async);
-    mbgl::ActorRef<TestWorker> workerRef(worker, mailbox);
+    ActorRef<TestWorker> workerRef(worker, mailbox);
 
     for (unsigned i = 0; i < numThreads; ++i) {
         // The callback runs on the worker, thus the atomic type.
diff --git a/test/util/memory.test.cpp b/test/util/memory.test.cpp
index e3ad976432..8602e6ac5b 100644
--- a/test/util/memory.test.cpp
+++ b/test/util/memory.test.cpp
@@ -5,7 +5,6 @@
 
 #include <mbgl/map/map_options.hpp>
 #include <mbgl/gl/headless_frontend.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/util/io.hpp>
 #include <mbgl/util/run_loop.hpp>
 #include <mbgl/style/style.hpp>
@@ -37,7 +36,6 @@ public:
 
     util::RunLoop runLoop;
     std::shared_ptr<StubFileSource> fileSource = std::make_shared<StubFileSource>();
-    ThreadPool threadPool { 4 };
 
 private:
     Response response(const std::string& path) {
@@ -72,8 +70,8 @@ TEST(Memory, Vector) {
     MemoryTest test;
     float ratio { 2 };
 
-    HeadlessFrontend frontend { { 256, 256 }, ratio, test.threadPool };
-    MapAdapter map(frontend, MapObserver::nullObserver(), test.fileSource, test.threadPool,
+    HeadlessFrontend frontend { { 256, 256 }, ratio };
+    MapAdapter map(frontend, MapObserver::nullObserver(), test.fileSource,
                    MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()).withPixelRatio(ratio));
     map.jumpTo(CameraOptions().withZoom(16));
     map.getStyle().loadURL("mapbox://streets");
@@ -85,8 +83,8 @@ TEST(Memory, Raster) {
     MemoryTest test;
     float ratio { 2 };
 
-    HeadlessFrontend frontend { { 256, 256 }, ratio, test.threadPool };
-    MapAdapter map(frontend, MapObserver::nullObserver(), test.fileSource, test.threadPool,
+    HeadlessFrontend frontend { { 256, 256 }, ratio };
+    MapAdapter map(frontend, MapObserver::nullObserver(), test.fileSource,
                    MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()).withPixelRatio(ratio));
     map.getStyle().loadURL("mapbox://satellite");
 
@@ -123,8 +121,8 @@ TEST(Memory, Footprint) {
     class FrontendAndMap {
     public:
         FrontendAndMap(MemoryTest& test_, const char* style)
-            : frontend(Size{ 256, 256 }, 2, test_.threadPool)
-            , map(frontend, MapObserver::nullObserver(), test_.fileSource, test_.threadPool,
+            : frontend(Size{ 256, 256 }, 2)
+            , map(frontend, MapObserver::nullObserver(), test_.fileSource,
                   MapOptions().withMapMode(MapMode::Static).withSize(frontend.getSize()).withPixelRatio(2)) {
             map.jumpTo(CameraOptions().withZoom(16));
             map.getStyle().loadURL(style);
diff --git a/test/util/thread.test.cpp b/test/util/thread.test.cpp
index 2bcb9d8959..49735585c6 100644
--- a/test/util/thread.test.cpp
+++ b/test/util/thread.test.cpp
@@ -1,8 +1,9 @@
+#include <mbgl/util/thread.hpp>
+
 #include <mbgl/actor/actor_ref.hpp>
+#include <mbgl/actor/scheduler.hpp>
 #include <mbgl/test/util.hpp>
-#include <mbgl/util/default_thread_pool.hpp>
 #include <mbgl/util/run_loop.hpp>
-#include <mbgl/util/thread.hpp>
 #include <mbgl/util/timer.hpp>
 
 #include <atomic>
@@ -139,8 +140,7 @@ TEST(Thread, Concurrency) {
     unsigned numMessages = 100000;
     std::atomic_uint completed(numMessages);
 
-    ThreadPool threadPool(10);
-    Actor<TestWorker> poolWorker(threadPool);
+    Actor<TestWorker> poolWorker(Scheduler::GetBackground());
     auto poolWorkerRef = poolWorker.self();
 
     Thread<TestWorker> threadedObject("Test");
@@ -165,8 +165,7 @@ TEST(Thread, Concurrency) {
 TEST(Thread, ThreadPoolMessaging) {
     auto loop = std::make_shared<RunLoop>();
 
-    ThreadPool threadPool(1);
-    Actor<TestWorker> poolWorker(threadPool);
+    Actor<TestWorker> poolWorker(Scheduler::GetBackground());
     auto poolWorkerRef = poolWorker.self();
 
     Thread<TestWorker> threadedObject("Test");