code: public synchronized static void initGlobal(ContextFactory factory)
      {
          if (factory == null) {
              throw new IllegalArgumentException();
          }
          if (hasCustomGlobal) {
              throw new IllegalStateException();
          }
          hasCustomGlobal = true;
          global = factory;
      }
docs: Set global ContextFactory.
  The method can only be called once.
  
  @see #getGlobal()
  @see #hasExplicitGlobal()