code: public Executor fixedContextExecutor(final Executor e) {
      final class FixedContextExecutor implements Executor {
        @Override
        public void execute(Runnable r) {
          e.execute(wrap(r));
        }
      }
  
      return new FixedContextExecutor();
    }
docs: Wrap an {@link Executor} so that it always executes with this context as the {@link #current}
  context. It is generally expected that {@link #currentContextExecutor(Executor)} would be
  used more commonly than this method.
  
  <p>One scenario in which this executor may be useful is when a single thread is sharding work
  to multiple threads.
  
  @see #currentContextExecutor(Executor)