[Bug] Lock not released correctly

[tianping526]

Before Creating the Bug Report

• I found a bug, not just asking a question, which should be created in GitHub Discussions.

• I have searched the GitHub Issues and GitHub Discussions of this repository and believe that this is not a duplicate.

• I have confirmed that this bug belongs to the current repository, not other repositories of RocketMQ.

Programming Language of the Client

Go

Runtime Platform Environment

5.8.0-43-generic #49~20.04.1-Ubuntu SMP Fri Feb 5 09:57:56 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

RocketMQ Version of the Client/Server

github.com/apache/rocketmq-clients/golang/v5 v5.0.1-rc.3

Run or Compiler Version

No response

Describe the Bug

rocketmq-clients/golang/[email protected]/rpc_client.go

func (rc *rpcClient) GracefulStop() error {
	rc.mux.Lock()
	sugarBaseLogger.Warnf("close rpc client, target=%s", rc.target)
	closeResult := rc.conn.Close()
	rc.mux.Lock()
	return closeResult
}

the GracefulStop method did not release the lock correctly

Steps to Reproduce

calling GracefulStop method in parallel, the second concurrent process will block permanently

What Did You Expect to See?

Lock is released correctly

What Did You See Instead?

Lock not released correctly

Additional Context

No response