wip simpler locking q

src/overlay_params.cpp

@@ -46,14 +46,13 @@ static void apply_params(overlay_params& params, const overlay_params& old_param
 overlay_params_mutexed g_overlay_params;
 void overlay_params_mutexed::assign(overlay_params& r)
 {
-   std::unique_lock<std::mutex> lk(m);
-   ++waiting_writers;
-   writer_cv.wait(lk, [&](){ return active_readers == 0 && active_writers == 0; });
-   ++active_writers;
+   std::unique_lock<std::mutex> lk(writer_mutex);
+   writer_cv.wait(lk, [&](){ return readers == 0 && writers == 0; });
+   ++writers;
    apply_params(r, instance);
    instance = r;
-   --waiting_writers;
-   --active_writers;
+   SPDLOG_DEBUG("{}", __func__);
+   --writers;
    reader_cv.notify_all();
 }
 

src/overlay_params.h

@@ -295,10 +295,10 @@ private:
 
 class overlay_params_mutexed {
    overlay_params instance;
-   std::mutex m;
+   std::mutex writer_mutex;
    std::condition_variable reader_cv;
    std::condition_variable writer_cv;
-   std::atomic_size_t waiting_writers, active_readers, active_writers;
+   std::atomic_size_t writers, readers;
 public:
    overlay_params_mutexed() = default;
    overlay_params_mutexed(const overlay_params_mutexed&) = delete;
@@ -327,14 +327,25 @@ public:
 
    overlay_params_wrapper get()
    {
-      std::unique_lock<std::mutex> lk(m);
-      // If get() is called again from a sub function, it may block on waiting writers so just continue if active_readers > 0
-      reader_cv.wait(lk, [&](){ return waiting_writers == 0 || active_readers > 0; });
-      ++active_readers;
+      do
+      {
+         if (writers > 0)
+         {
+            std::unique_lock<std::mutex> lk(writer_mutex);
+            // If get() is called again from a sub function, it may block on waiting writers so just continue if active_readers > 0
+            reader_cv.wait(lk, [&](){ return writers == 0 || readers > 0; });
+         }
+
+         ++readers;
+         if (writers == 0)
+            break;
+         --readers;
+      } while(true);
+
       return {
          instance,
          [&]() -> void {
-            --active_readers;
+            --readers;
             writer_cv.notify_all();
          }
       };