diff --git a/clientv3/concurrency/mutex.go b/clientv3/concurrency/mutex.go index cee15db7b..83df27c79 100644 --- a/clientv3/concurrency/mutex.go +++ b/clientv3/concurrency/mutex.go @@ -49,7 +49,9 @@ func (m *Mutex) Lock(ctx context.Context) error { put := v3.OpPut(m.myKey, "", v3.WithLease(s.Lease())) // reuse key in case this session already holds the lock get := v3.OpGet(m.myKey) - resp, err := client.Txn(ctx).If(cmp).Then(put).Else(get).Commit() + // 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 } @@ -57,6 +59,12 @@ func (m *Mutex) Lock(ctx context.Context) error { 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)