Forward declarations are your friends

Why leak gl headers into most of kicad

include/singleton.h

@@ -21,37 +21,25 @@
 #define KICAD_SINGLETON_H
 
 #include <advanced_config.h>
-#include <bs_thread_pool.hpp>
-#include <gal/opengl/gl_context_mgr.h>
+
+class GL_CONTEXT_MANAGER;
+namespace BS
+{
+class thread_pool;
+}
 
 class KICAD_SINGLETON
 {
 public:
     KICAD_SINGLETON(){};
 
-    ~KICAD_SINGLETON()
-    {
-        // This will wait for all threads to finish and then join them to the main thread
-        delete m_ThreadPool;
-
-        m_ThreadPool = nullptr;
-
-        m_GLContextManager->DeleteAll();
-        delete m_GLContextManager;
-        m_GLContextManager = nullptr;
-    };
+    ~KICAD_SINGLETON();
 
 
-    void Init()
-    {
-        int num_threads = std::max( 0, ADVANCED_CFG::GetCfg().m_MaximumThreads );
-        m_ThreadPool = new BS::thread_pool( num_threads );
-        m_GLContextManager = new GL_CONTEXT_MANAGER();
-    }
+    void Init();
 
     BS::thread_pool* m_ThreadPool;
     GL_CONTEXT_MANAGER* m_GLContextManager;
-
 };