refactor(server): replace chunk set with flat_hash_set and add ref count

- Replace std::unordered_set with absl::flat_hash_set for chunk position sets.
- Add ref_count field to ChunkEntity and implement update_ref_count().
- Remove clear_unused_chunks() and use ref counting for chunk lifetime.
- Add get_chunk_pos_set() accessors to ServerPlayer.

include/Cubed/gameplay/server_player.hpp

@@ -2,20 +2,20 @@
 #include "Cubed/gameplay/chunk_pos.hpp"
 #include "Cubed/gameplay/game_time.hpp"
 
+#include <absl/container/flat_hash_set.h>
 #include <atomic>
 #include <glm/glm.hpp>
 #include <memory>
 #include <shared_mutex>
 #include <string>
 #include <string_view>
-#include <unordered_set>
 namespace Cubed {
 class ServerWorld;
 class Session;
 class ServerPlayer {
-    using ChunkPosSet = std::unordered_set<ChunkPos, ChunkPos::Hash>;
 
 public:
+    using ChunkPosSet = absl::flat_hash_set<ChunkPos, ChunkPos::Hash>;
     ServerPlayer(const ServerPlayer&) = delete;
     ServerPlayer(ServerPlayer&&) = delete;
     ServerPlayer& operator=(const ServerPlayer&) = delete;
@@ -23,7 +23,6 @@ public:
     ServerPlayer(std::string_view name, std::string_view uuid,
                  ServerWorld& m_world, std::shared_ptr<Session> session,
                  TickType gametick);
-    using PlayerChunkPosSet = std::unordered_set<ChunkPos, ChunkPos::Hash>;
 
     const glm::vec3& get_pos() const;
     const std::string& get_name() const;
@@ -36,6 +35,8 @@ public:
     void task_id(int id);
     bool has_player(ChunkPos pos) const;
     void update_chunk_set(const ChunkPosSet& set);
+    const ChunkPosSet& get_chunk_pos_set() const;
+    ChunkPosSet& get_chunk_pos_set();
 
 private:
     static constexpr TickType TIMEOUT = 200;
@@ -48,6 +49,6 @@ private:
     std::atomic<TickType> m_last_gametick{0};
     std::atomic<int> m_chunk_task_id{0};
     mutable std::shared_mutex m_chunk_pos_mutex;
-    PlayerChunkPosSet m_player_chunk_pos_set;
+    ChunkPosSet m_player_chunk_pos_set;
 };
 } // namespace Cubed

include/Cubed/gameplay/server_world.hpp

@@ -10,13 +10,13 @@
 #include "Cubed/tools/thread_pool.hpp"
 #include "world/block_change.pb.h"
 
+#include <absl/container/flat_hash_set.h>
 #include <future>
 #include <shared_mutex>
 #include <tbb/concurrent_hash_map.h>
 #include <tbb/concurrent_queue.h>
 #include <tbb/concurrent_unordered_map.h>
 #include <unordered_map>
-#include <unordered_set>
 #include <utility>
 #include <vector>
 namespace Cubed {
@@ -91,6 +91,7 @@ private:
     struct ChunkEntity {
         ChunkState state;
         std::shared_ptr<ServerChunk> chunk;
+        uint32_t ref_count = 0;
     };
 
     enum class ChunkLoadStyle { RANDOM, CENTER };
@@ -113,7 +114,7 @@ private:
     using PlayerHashMap = std::unordered_map<std::string, ServerPlayer>;
     using PendingChunkHashMap =
         std::unordered_map<ChunkPos, PendingChunk, ChunkPos::Hash>;
-    using ChunkPosSet = std::unordered_set<ChunkPos, ChunkPos::Hash>;
+    using ChunkPosSet = absl::flat_hash_set<ChunkPos, ChunkPos::Hash>;
     using PlayerUUIDMap = tbb::concurrent_hash_map<std::string, std::string>;
 
     using uuid_acc = PlayerUUIDMap::accessor;
@@ -177,7 +178,7 @@ private:
     void poll_finished_chunks();
     void wait_all_chunk_tasks();
 
-    void clear_unused_chunks();
+    void update_ref_count(const ChunkPosSet& old, const ChunkPosSet& now);
 
     void send_time();