[core] allow safe direct access to actor on single threaded scheduler

2 files changed, 37 insertions, 0 deletions

diff --git a/include/mbgl/actor/actor.hpp b/include/mbgl/actor/actor.hpp
index a0df19208e..93de4a948f 100644
--- a/include/mbgl/actor/actor.hpp
+++ b/include/mbgl/actor/actor.hpp
@@ -45,6 +45,11 @@ namespace mbgl {
     purpose of the actor model: prohibiting direct concurrent access to shared state.
 */
 
+
+namespace util {
+template <class> class Thread;
+} // namespace util
+
 template <class Object>
 class Actor : public util::noncopyable {
 public:
@@ -91,6 +96,9 @@ public:
     }
 
 private:
+    template<typename U>
+    friend class util::Thread;
+
     std::shared_ptr<Mailbox> mailbox;
     Object object;
 };
diff --git a/include/mbgl/util/thread.hpp b/include/mbgl/util/thread.hpp
index 2a58e618da..6f6fc13f0a 100644
--- a/include/mbgl/util/thread.hpp
+++ b/include/mbgl/util/thread.hpp
@@ -125,6 +125,13 @@ public:
     }
 
 private:
+    template <class U>
+    friend class BlockingThreadGuard;
+
+    Object& getObject() {
+        return object->object;
+    }
+
     MBGL_STORE_THREAD(tid);
 
     void schedule(std::weak_ptr<Mailbox> mailbox) override {
@@ -151,11 +158,33 @@ private:
     std::thread thread;
     std::unique_ptr<Actor<Object>> object;
 
+    std::mutex pauseMutex;
     std::unique_ptr<std::promise<void>> paused;
     std::unique_ptr<std::promise<void>> resumed;
 
     util::RunLoop* loop = nullptr;
 };
 
+
+template <class Object>
+class BlockingThreadGuard {
+public:
+    BlockingThreadGuard(Thread<Object>& thread_)
+        : thread(thread_) {
+        thread.pause();
+    }
+
+    ~BlockingThreadGuard() {
+        thread.resume();
+    }
+
+    Object& object() {
+        return thread.getObject();
+    }
+
+private:
+    Thread<Object>& thread;
+};
+
 } // namespace util
 } // namespace mbgl