Improve libevent threading initialization order

Use static initializer to call evthread_use_pthreads() at program startup,
before any other code (including curl) can initialize libevent. This fixes
the "evthread initialization must be called BEFORE anything else!" error
on systems where curl is compiled with libevent support.

Changes:
- Remove event_enable_debug_mode() which can only be called once and
  causes issues with shared libraries
- Use simple static initializer instead of constructor priority attribute
- evthread_use_pthreads() is safe to call multiple times

Author: RahulHere

src/event/libevent_dispatcher.cc

@@ -74,22 +74,35 @@ uint32_t fromLibeventEvents(short events) {
   return result;
 }
 
-// Lazy initialization for libevent threading support
-// Uses std::call_once to ensure thread-safe one-time initialization
-// This avoids blocking in static initialization which was causing hangs
-void ensureLibeventThreadingInitialized() {
-  static std::once_flag init_flag;
-  std::call_once(init_flag, []() {
+// Early initialization for libevent threading support
+// CRITICAL: This must run BEFORE any other libevent functions or libraries
+// that might use libevent (like curl with libevent support).
+// evthread_use_pthreads() is safe to call multiple times - it returns 0 after first call
+struct LibeventEarlyInit {
+  LibeventEarlyInit() {
 #ifdef _WIN32
     evthread_use_windows_threads();
 #else
     evthread_use_pthreads();
 #endif
-    // Enable debug mode in debug builds
-#ifndef NDEBUG
-    event_enable_debug_mode();
+    // NOTE: event_enable_debug_mode() is NOT called here because:
+    // 1. It can only be called once across the entire process
+    // 2. With shared libraries, this code may run from multiple TUs
+    // 3. Debug mode is only needed for debugging libevent internals
+  }
+};
+
+// Single static instance ensures initialization at program startup
+static LibeventEarlyInit s_libevent_early_init;
+
+// This function is kept for compatibility
+void ensureLibeventThreadingInitialized() {
+  // evthread functions are safe to call multiple times
+#ifdef _WIN32
+  evthread_use_windows_threads();
+#else
+  evthread_use_pthreads();
 #endif
-  });
 }
 
 }  // namespace