protected Subject getSubject() {
        return SecurityUtils.getSubject();
    }
Returns the currently Subject instance that should be associated with Runnable or Callable instances before
being dispatched to the target {@code Executor} instance.  This implementation merely defaults to returning
{@code SecurityUtils}.{@link SecurityUtils#getSubject() getSubject()}.

@return the currently Subject instance that should be associated with Runnable or Callable instances before
being dispatched to the target {@code Executor} instance.
core/src/main/java/org/apache/shiro/concurrent/SubjectAwareExecutor.java