Delete GL context in GL destructor not program

Also lock the DeleteAll call with mutext to protect threaded access.

The OpenGL contexts are removed when OPENGL_GAL class is destroyed.
Explicitly deleting all contexts prior to destroying the OPENGL_GAL
class causes an assert when the destructor tries to lock its context
prior to cleaning up OpenGL memory.  In most cases, an unhandled assert
in a destructor-called function will simply exit the destructor.

Python thread cleanup will also attempt to close the context.  This can
cause a race condition with multiple threads accessing/deleting the
canvas.

Fixes: lp:1774096
* https://bugs.launchpad.net/kicad/+bug/1774096

common/gl_context_mgr.cpp

@@ -65,10 +65,14 @@ void GL_CONTEXT_MANAGER::DestroyCtx( wxGLContext* aContext )
 
 void GL_CONTEXT_MANAGER::DeleteAll()
 {
+    m_glCtxMutex.lock();
+
     for( auto& ctx : m_glContexts )
         delete ctx.first;
 
     m_glContexts.clear();
+    m_glCtx = NULL;
+    m_glCtxMutex.unlock();
 }
 
 

pcbnew/pcbnew.cpp

@@ -372,12 +372,6 @@ bool IFACE::OnKifaceStart( PGM_BASE* aProgram, int aCtlBits )
 
 void IFACE::OnKifaceEnd()
 {
-    // This function deletes OpenGL contexts used (if any) by wxGLCanvas objects.
-    // It can be called only when closing the application, because it deletes an OpenGL context
-    // which can still be in usage. Destroying OpenGL contexts earlier may crash the application.
-    GL_CONTEXT_MANAGER::Get().DeleteAll();
-
-    end_common();
 #if defined( KICAD_SCRIPTING_WXPYTHON )
     // Restore the thread state and tell Python to cleanup after itself.
     // wxPython will do its own cleanup as part of that process.
@@ -386,4 +380,6 @@ void IFACE::OnKifaceEnd()
     if( IsWxPythonLoaded() )
         pcbnewFinishPythonScripting();
 #endif
+
+    end_common();
 }