You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mutex.go
    path of file: ./repos/learning/golang/practice/go-crontab/gopath/src/github.com/coreos/etcd/clientv3/concurrency
    
    the code of the file until where you have to start completion: // Copyright 2016 The etcd Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package conc
    
func (m *Mutex) Lock(ctx context.Context) error {
	s := m.s
	client := m.s.Client()

	m.myKey = fmt.Sprintf("%s%x", m.pfx, s.Lease())
	cmp := v3.Compare(v3.CreateRevision(m.myKey), "=", 0)
	// put self in lock waiters via myKey; oldest waiter holds lock
	put := v3.OpPut(m.myKey, "", v3.WithLease(s.Lease()))
	// reuse key in case this session already holds the lock
	get := v3.OpGet(m.myKey)
	// fetch current holder to complete uncontended path with only one RPC
	getOwner := v3.OpGet(m.pfx, v3.WithFirstCreate()...)
	resp, err := client.Txn(ctx).If(cmp).Then(put, getOwner).Else(get, getOwner).Commit()
	if err != nil {
		return err
	}
	m.myRev = resp.Header.Revision
	if !resp.Succeeded {
		m.myRev = resp.Responses[0].GetResponseRange().Kvs[0].CreateRevision
	}
	// if no key on prefix / the minimum rev is key, already hold the lock
	ownerKey := resp.Responses[1].GetResponseRange().Kvs
	if len(ownerKey) == 0 || ownerKey[0].CreateRevision == m.myRev {
		m.hdr = resp.Header
		return nil
	}

	// wait for deletion revisions prior to myKey
	hdr, werr := waitDeletes(ctx, client, m.pfx, m.myRev-1)
	// release lock key if cancelled
	select {
	case <-ctx.Done():
		m.Unlock(client.Ctx())
	default:
		m.hdr = hdr
	}
	return werr
}