[feat] add native Android controller

apps/android/native/latest_frame_worker.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <condition_variable>
+#include <functional>
+#include <mutex>
+#include <optional>
+#include <thread>
+#include <utility>
+
+namespace crossdesk::android_controller {
+// Rendering may wait for Surface buffers. Never hold up the decoder or build
+// a FIFO of obsolete pictures: keep at most one pending decoded frame.
+template <typename Frame>
+class LatestFrameWorker {
+ public:
+  explicit LatestFrameWorker(std::function<void(Frame)> render)
+      : render_(std::move(render)), thread_([this] { Run(); }) {}
+  ~LatestFrameWorker() { Stop(); }
+  LatestFrameWorker(const LatestFrameWorker&) = delete;
+  LatestFrameWorker& operator=(const LatestFrameWorker&) = delete;
+
+  bool Submit(Frame frame) {
+    std::lock_guard lock(mutex_);
+    if (stopped_) return false;
+    pending_ = std::move(frame);
+    changed_.notify_one();
+    return true;
+  }
+  void Clear() {
+    std::lock_guard lock(mutex_);
+    pending_.reset();
+  }
+  // Called by the session owner, before destroying the peer or Surface.
+  void Stop() {
+    {
+      std::lock_guard lock(mutex_);
+      stopped_ = true;
+      pending_.reset();
+    }
+    changed_.notify_one();
+    if (thread_.joinable()) thread_.join();
+  }
+
+ private:
+  void Run() {
+    for (;;) {
+      std::unique_lock lock(mutex_);
+      changed_.wait(lock, [this] { return stopped_ || pending_.has_value(); });
+      if (stopped_) return;
+      Frame frame = std::move(*pending_);
+      pending_.reset();
+      lock.unlock();
+      render_(std::move(frame));
+    }
+  }
+  const std::function<void(Frame)> render_;
+  std::mutex mutex_;
+  std::condition_variable changed_;
+  std::optional<Frame> pending_;
+  bool stopped_ = false;
+  std::thread thread_;
+};
+}  // namespace crossdesk::android_controller