Allow multiple epoll instances on server

src/server.hpp

@@ -103,11 +103,14 @@ private:
   std::vector<std::thread> threads_;
   std::atomic<int64_t> connection_id_{0};
 
+  // Round-robin counter for connection distribution
+  std::atomic<size_t> connection_distribution_counter_{0};
+
   // Shutdown coordination
   int shutdown_pipe_[2] = {-1, -1};
 
-  // Epoll file descriptor
-  int epollfd_ = -1;
+  // Multiple epoll file descriptors to reduce contention
+  std::vector<int> epoll_fds_;
   int listen_sockfd_ = -1;
 
   // Unique tags for special events to avoid type confusion in epoll data union
@@ -118,14 +121,19 @@ private:
   void setup_shutdown_pipe();
   void setup_signal_handling();
   int create_listen_socket();
+  void create_epoll_instances();
   void start_io_threads();
   void cleanup_resources();
 
+  // Helper to get epoll fd for a thread using round-robin
+  int get_epoll_for_thread(int thread_id) const;
+
   // Helper for processing connection I/O
   void process_connection_io(std::unique_ptr<Connection> &conn, int events);
 
   // Helper for processing a batch of connections with their events
-  void process_connection_batch(std::span<std::unique_ptr<Connection>> batch,
+  void process_connection_batch(int epollfd,
+                                std::span<std::unique_ptr<Connection>> batch,
                                 std::span<const int> events, bool is_new);
 
   /**