With latest develop tip, in Xcode 9.1 (9B55), running the OpenGL demo triggers a runtime warnings, which Xcode now helpfully provides in the errors pane on the left.
According to its warning
[NSView frame] is not supposed to be used by non-main thread. In this case the OpenGL rendering thread calls
OpenGLContext::CachedImage::updateViewportSize which in turn causes
NSViewComponentPeer to call the forbidden method.