1 files changed, 50 insertions, 8 deletions
diff --git a/src/mbgl/util/thread_pool.hpp b/src/mbgl/util/thread_pool.hpp
index 509fd06061..7642f9b4ca 100644
--- a/src/mbgl/util/thread_pool.hpp
+++ b/src/mbgl/util/thread_pool.hpp
@@ -3,6 +3,7 @@
 #include <mbgl/actor/mailbox.hpp>
 #include <mbgl/actor/scheduler.hpp>
 
+#include <array>
 #include <condition_variable>
 #include <mutex>
 #include <queue>
@@ -10,19 +11,60 @@
 
 namespace mbgl {
 
-class ThreadPool final : public Scheduler {
+class ThreadedSchedulerBase : public Scheduler {
 public:
-    explicit ThreadPool(std::size_t count);
-    ~ThreadPool() override;
+    void schedule(std::function<void()>) override;
 
-    void schedule(std::weak_ptr<Mailbox>) override;
+protected:
+    ThreadedSchedulerBase() = default;
+    ~ThreadedSchedulerBase() override;
 
-private:
-    std::vector<std::thread> threads;
-    std::queue<std::weak_ptr<Mailbox>> queue;
+    void terminate();
+    std::thread makeSchedulerThread(size_t index);
+
+    std::queue<std::function<void()>> queue;
     std::mutex mutex;
     std::condition_variable cv;
-    bool terminate{ false };
+    bool terminated{false};
+};
+
+/**
+ * @brief ThreadScheduler implements Scheduler interface using a lightweight event loop
+ *
+ * @tparam N number of threads
+ *
+ * Note: If N == 1 all scheduled tasks are guaranteed to execute consequently;
+ * otherwise, some of the scheduled tasks might be executed in parallel.
+ */
+template <std::size_t N>
+class ThreadedScheduler : public ThreadedSchedulerBase {
+public:
+    ThreadedScheduler() {
+        for (std::size_t i = 0u; i < N; ++i) {
+            threads[i] = makeSchedulerThread(i);
+        }
+    }
+
+    ~ThreadedScheduler() override {
+        terminate();
+        for (auto& thread : threads) {
+            thread.join();
+        }
+    }
+
+    mapbox::base::WeakPtr<Scheduler> makeWeakPtr() override { return weakFactory.makeWeakPtr(); }
+
+private:
+    std::array<std::thread, N> threads;
+    mapbox::base::WeakPtrFactory<Scheduler> weakFactory{this};
+    static_assert(N > 0, "Thread count must be more than zero.");
 };
 
+using SequencedScheduler = ThreadedScheduler<1>;
+
+template <std::size_t extra>
+using ParallelScheduler = ThreadedScheduler<1 + extra>;
+
+using ThreadPool = ParallelScheduler<3>;
+
 } // namespace mbgl