speed up images with libcurl multi, raise concurrency

also maybe fix some rare crash

filecache.hpp

@@ -1,13 +1,58 @@
 #pragma once
+#include <curl/curl.h>
 #include <functional>
 #include <string>
 #include <filesystem>
 #include <vector>
+#include <unordered_set>
 #include <unordered_map>
 #include <future>
+#include <mutex>
 #include "util.hpp"
 #include "http.hpp"
 
+class FileCacheWorkerThread {
+public:
+    using callback_type = sigc::slot<void(std::string path)>;
+
+    FileCacheWorkerThread();
+    ~FileCacheWorkerThread();
+
+    void set_file_path(const std::filesystem::path &path);
+
+    void add_image(const std::string &string, callback_type callback);
+
+    void stop();
+
+private:
+    void loop();
+
+    bool m_stop = false;
+    std::thread m_thread;
+
+    struct QueueEntry {
+        std::string URL;
+        callback_type Callback;
+    };
+
+    std::condition_variable m_cv;
+
+    mutable std::mutex m_queue_mutex;
+    std::queue<QueueEntry> m_queue;
+
+    std::unordered_map<CURL *, FILE *> m_curl_file_handles;
+    std::unordered_map<CURL *, std::string> m_handle_urls;
+    std::unordered_map<std::string, std::filesystem::path> m_paths;
+    std::unordered_map<std::string, callback_type> m_callbacks;
+
+    int m_running_handles = 0;
+
+    std::unordered_set<CURL *> m_handles;
+    CURLM *m_multi_handle;
+
+    std::filesystem::path m_data_path;
+};
+
 class Cache {
 public:
     Cache();
@@ -19,16 +64,16 @@ public:
     void ClearCache();
 
 private:
-    std::string GetCachedName(std::string str);
     void CleanupFutures();
     void RespondFromPath(std::filesystem::path path, callback_type cb);
-    void OnResponse(const http::response_type &r);
-
-    std::unique_ptr<Semaphore> m_semaphore;
+    void OnResponse(const std::string &url);
+    void OnFetchComplete(const std::string &url);
 
     std::unordered_map<std::string, std::vector<callback_type>> m_callbacks;
     std::vector<std::future<void>> m_futures;
     std::filesystem::path m_tmp_path;
 
-    bool m_canceled = false;
+    mutable std::mutex m_mutex;
+
+    FileCacheWorkerThread m_worker;
 };