[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, 16 insertions, 7 deletions

diff --git a/platform/node/src/node_map.cpp b/platform/node/src/node_map.cpp
index 7156a1f1bf..0a7da3a83a 100644
--- a/platform/node/src/node_map.cpp
+++ b/platform/node/src/node_map.cpp
@@ -630,8 +630,8 @@ void NodeMap::cancel() {
         reinterpret_cast<NodeMap *>(h->data)->renderFinished();
     });
 
-    frontend = std::make_unique<mbgl::HeadlessFrontend>(mbgl::Size{ 256, 256 }, pixelRatio, threadpool);
-    map = std::make_unique<mbgl::Map>(*frontend, mapObserver, threadpool,
+    frontend = std::make_unique<mbgl::HeadlessFrontend>(mbgl::Size{ 256, 256 }, pixelRatio);
+    map = std::make_unique<mbgl::Map>(*frontend, mapObserver,
                                       mbgl::MapOptions().withSize(frontend->getSize())
                                       .withPixelRatio(pixelRatio)
                                       .withMapMode(mode)
@@ -1214,8 +1214,8 @@ NodeMap::NodeMap(v8::Local<v8::Object> options)
             : true;
     }())
     , mapObserver(NodeMapObserver())
-    , frontend(std::make_unique<mbgl::HeadlessFrontend>(mbgl::Size { 256, 256 }, pixelRatio, threadpool))
-    , map(std::make_unique<mbgl::Map>(*frontend, mapObserver, threadpool,
+    , frontend(std::make_unique<mbgl::HeadlessFrontend>(mbgl::Size { 256, 256 }, pixelRatio))
+    , map(std::make_unique<mbgl::Map>(*frontend, mapObserver,
                                       mbgl::MapOptions().withSize(frontend->getSize())
                                       .withPixelRatio(pixelRatio)
                                       .withMapMode(mode)
diff --git a/platform/node/src/node_map.hpp b/platform/node/src/node_map.hpp
index 65664b34bb..d45dbec92b 100644
--- a/platform/node/src/node_map.hpp
+++ b/platform/node/src/node_map.hpp
@@ -1,7 +1,5 @@
 #pragma once
 
-#include "node_thread_pool.hpp"
-
 #include <mbgl/map/map.hpp>
 #include <mbgl/storage/file_source.hpp>
 #include <mbgl/util/image.hpp>
@@ -79,7 +77,6 @@ public:
     const float pixelRatio;
     mbgl::MapMode mode;
     bool crossSourceCollisions;
-    NodeThreadPool threadpool;
     NodeMapObserver mapObserver;
     std::unique_ptr<mbgl::HeadlessFrontend> frontend;
     std::unique_ptr<mbgl::Map> map;
diff --git a/platform/node/src/node_thread_pool.cpp b/platform/node/src/node_thread_pool.cpp
index 1f37565e8a..de403c605c 100644
--- a/platform/node/src/node_thread_pool.cpp
+++ b/platform/node/src/node_thread_pool.cpp
@@ -2,6 +2,7 @@
 #include "util/async_queue.hpp"
 
 #include <mbgl/actor/mailbox.hpp>
+#include <mbgl/platform/background_scheduler.hpp>
 
 namespace node_mbgl {
 
@@ -35,3 +36,14 @@ void NodeThreadPool::Worker::WorkComplete() {
 }
 
 } // namespace node_mbgl
+
+namespace mbgl {
+namespace platform {
+
+Scheduler& GetBackgroundScheduler() {
+    static node_mbgl::NodeThreadPool pool;
+    return pool;
+}
+
+} // namespace platform
+} // namespace mbgl