@Override
    public void shutdown() {
        if (!this.started) {
            return;
        }
        if (this.raftGroupService != null) {
            this.raftGroupService.shutdown();
            try {
                this.raftGroupService.join();
            } catch (final InterruptedException e) {
                ThrowUtil.throwException(e);
            }
        }
        this.started = false;
        LOG.info("[ElectionNode] shutdown successfully: {}.", this);
    }
Set priority value, required for priority-based election, it must be a positive value when
enable the feature, some special value meaning:
<ul>
<li>-1 : disable priority-based election.</li>
<li>0: will never participate in election.</li>
<li>1: minimum value</li>
</ul>
value.
jraft-example/src/main/java/com/alipay/sofa/jraft/example/priorityelection/PriorityElectionNode.java