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concurrency: fetch current lock holder when creating waitlist key

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The uncontended path for a mutex would fetch the minimum
revision key on the prefix after creating its entry in
the wait list. This fetch can be rolled into the txn for
creating the wait key, eliminating a round-trip for immediately
acquiring the lock.
This commit is contained in:
Anthony Romano 2017-06-15 08:10:05 -07:00
parent 1f206c027a
commit f5b96991a1
1 changed files with 9 additions and 1 deletions
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10
clientv3/concurrency/mutex.go
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@ -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)