git subrepo clone (merge) https://github.com/free-audio/clap-helpers.git deps/clap-juce-extensions/clap-libs/clap-helpers

subrepo:
  subdir:   "deps/clap-juce-extensions/clap-libs/clap-helpers"
  merged:   "2bb43c187"
upstream:
  origin:   "https://github.com/free-audio/clap-helpers.git"
  branch:   "main"
  commit:   "2bb43c187"
git-subrepo:
  version:  "0.4.3"
  origin:   "https://github.com/ingydotnet/git-subrepo.git"
  commit:   "2f68596"

deps/clap-juce-extensions/clap-libs/clap-helpers/include/clap/helpers/reducing-param-queue.hh

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <atomic>
+#include <cstddef>
+#include <functional>
+#include <unordered_map>
+
+#include <clap/private/macros.h>
+
+namespace clap { namespace helpers {
+
+#ifdef CLAP_HAS_CXX20
+   template <typename T>
+   concept UpdatableValue = requires(T &a, const T &b) {
+      // update a with b, b being newer than a
+      { a.update(b) };
+   };
+#endif
+
+   // TODO: when switching to C++20
+   // template <typename K, UpdatableValue V>
+   template <typename K, typename V>
+   class ReducingParamQueue {
+   public:
+      using key_type = K;
+      using value_type = V;
+      using queue_type = std::unordered_map<key_type, value_type>;
+      using consumer_type = const std::function<void(const key_type &key, const value_type &value)>;
+
+      ReducingParamQueue();
+
+      void setCapacity(size_t capacity);
+
+      void set(const key_type &key, const value_type &value);
+      void setOrUpdate(const key_type &key, const value_type &value);
+      void producerDone();
+
+      void consume(const consumer_type &consumer);
+
+      void reset();
+
+   private:
+      queue_type _queues[2];
+      std::atomic<queue_type *> _free = nullptr;
+      std::atomic<queue_type *> _producer = nullptr;
+      std::atomic<queue_type *> _consumer = nullptr;
+   };
+}} // namespace clap::helpers