@Override
    public synchronized void shutdown() {
        if (this.rpcClient != null) {
            this.rpcClient.shutdown();
            this.rpcClient = null;
            this.rpcExecutor.shutdown();
        }
    }
Abstract RPC client service based.
@author boyan (boyan@alibaba-inc.com)
@author jiachun.fjc
jraft-core/src/main/java/com/alipay/sofa/jraft/rpc/impl/AbstractClientService.java