Merge pull request #4604 from heyitsanthony/etcdctl-lock

etcdctlv3: lock command

clientv3/concurrency/key.go

@@ -0,0 +1,57 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// 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 concurrency
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	v3 "github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/etcdserver/api/v3rpc"
+)
+
+// NewUniqueKey creates a new key from a given prefix.
+func NewUniqueKey(ctx context.Context, kv v3.KV, pfx string, opts ...v3.OpOption) (string, int64, error) {
+	for {
+		newKey := fmt.Sprintf("%s/%v", pfx, time.Now().UnixNano())
+		put := v3.OpPut(newKey, "", opts...)
+		cmp := v3.Compare(v3.ModifiedRevision(newKey), "=", 0)
+		resp, err := kv.Txn(ctx).If(cmp).Then(put).Commit()
+		if err != nil {
+			return "", 0, err
+		}
+		if !resp.Succeeded {
+			continue
+		}
+		return newKey, resp.Header.Revision, nil
+	}
+}
+
+func waitUpdate(ctx context.Context, client *v3.Client, key string, opts ...v3.OpOption) error {
+	w := v3.NewWatcher(client)
+	defer w.Close()
+	wc := w.Watch(ctx, key, opts...)
+	if wc == nil {
+		return ctx.Err()
+	}
+	wresp, ok := <-wc
+	if !ok {
+		return ctx.Err()
+	}
+	if len(wresp.Events) == 0 {
+		return v3rpc.ErrCompacted
+	}
+	return nil
+}

clientv3/concurrency/mutex.go

@@ -0,0 +1,113 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// 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 concurrency
+
+import (
+	"sync"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	v3 "github.com/coreos/etcd/clientv3"
+)
+
+// Mutex implements the sync Locker interface with etcd
+type Mutex struct {
+	client *v3.Client
+	kv     v3.KV
+	ctx    context.Context
+
+	pfx   string
+	myKey string
+	myRev int64
+}
+
+func NewMutex(ctx context.Context, client *v3.Client, pfx string) *Mutex {
+	return &Mutex{client, v3.NewKV(client), ctx, pfx, "", -1}
+}
+
+// Lock locks the mutex with a cancellable context. If the context is cancelled
+// while trying to acquire the lock, the mutex tries to clean its stale lock entry.
+func (m *Mutex) Lock(ctx context.Context) error {
+	s, err := NewSession(m.client)
+	if err != nil {
+		return err
+	}
+	// put self in lock waiters via myKey; oldest waiter holds lock
+	m.myKey, m.myRev, err = NewUniqueKey(ctx, m.kv, m.pfx, v3.WithLease(s.Lease()))
+	// wait for lock to become available
+	for err == nil {
+		// find oldest element in waiters via revision of insertion
+		var resp *v3.GetResponse
+		resp, err = m.kv.Get(ctx, m.pfx, v3.WithFirstRev()...)
+		if err != nil {
+			break
+		}
+		if m.myRev == resp.Kvs[0].CreateRevision {
+			// myKey is oldest in waiters; myKey holds the lock now
+			return nil
+		}
+		// otherwise myKey isn't lowest, so there must be a pfx prior to myKey
+		opts := append(v3.WithLastRev(), v3.WithRev(m.myRev-1))
+		resp, err = m.kv.Get(ctx, m.pfx, opts...)
+		if err != nil {
+			break
+		}
+		lastKey := string(resp.Kvs[0].Key)
+		// wait for release on prior pfx
+		err = waitUpdate(ctx, m.client, lastKey, v3.WithRev(m.myRev))
+		// try again in case lastKey left the wait list before acquiring the lock;
+		// myKey can only hold the lock if it's the oldest in the list
+	}
+
+	// release lock key if cancelled
+	select {
+	case <-ctx.Done():
+		m.Unlock()
+	default:
+	}
+	return err
+}
+
+func (m *Mutex) Unlock() error {
+	if _, err := m.kv.Delete(m.ctx, m.myKey); err != nil {
+		return err
+	}
+	m.myKey = "\x00"
+	m.myRev = -1
+	return nil
+}
+
+func (m *Mutex) IsOwner() v3.Cmp {
+	return v3.Compare(v3.CreatedRevision(m.myKey), "=", m.myRev)
+}
+
+func (m *Mutex) Key() string { return m.myKey }
+
+type lockerMutex struct{ *Mutex }
+
+func (lm *lockerMutex) Lock() {
+	if err := lm.Mutex.Lock(lm.ctx); err != nil {
+		panic(err)
+	}
+}
+func (lm *lockerMutex) Unlock() {
+	if err := lm.Mutex.Unlock(); err != nil {
+		panic(err)
+	}
+}
+
+// NewLocker creates a sync.Locker backed by an etcd mutex.
+func NewLocker(ctx context.Context, client *v3.Client, pfx string) sync.Locker {
+	return &lockerMutex{NewMutex(ctx, client, pfx)}
+}

clientv3/concurrency/session.go

@@ -0,0 +1,106 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// 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 concurrency
+
+import (
+	"sync"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	v3 "github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/lease"
+)
+
+// only keep one ephemeral lease per client
+var clientSessions clientSessionMgr = clientSessionMgr{sessions: make(map[*v3.Client]*Session)}
+
+const sessionTTL = 60
+
+type clientSessionMgr struct {
+	sessions map[*v3.Client]*Session
+	mu       sync.Mutex
+}
+
+// Session represents a lease kept alive for the lifetime of a client.
+// Fault-tolerant applications may use sessions to reason about liveness.
+type Session struct {
+	client *v3.Client
+	id     lease.LeaseID
+
+	cancel context.CancelFunc
+	donec  <-chan struct{}
+}
+
+// NewSession gets the leased session for a client.
+func NewSession(client *v3.Client) (*Session, error) {
+	clientSessions.mu.Lock()
+	defer clientSessions.mu.Unlock()
+	if s, ok := clientSessions.sessions[client]; ok {
+		return s, nil
+	}
+
+	lc := v3.NewLease(client)
+	resp, err := lc.Create(context.TODO(), sessionTTL)
+	if err != nil {
+		return nil, err
+	}
+	id := lease.LeaseID(resp.ID)
+
+	ctx, cancel := context.WithCancel(context.Background())
+	keepAlive, err := lc.KeepAlive(ctx, id)
+	if err != nil || keepAlive == nil {
+		return nil, err
+	}
+
+	donec := make(chan struct{})
+	s := &Session{client: client, id: id, cancel: cancel, donec: donec}
+	clientSessions.sessions[client] = s
+
+	// keep the lease alive until client error or cancelled context
+	go func() {
+		defer func() {
+			clientSessions.mu.Lock()
+			delete(clientSessions.sessions, client)
+			clientSessions.mu.Unlock()
+			lc.Close()
+			close(donec)
+		}()
+		for range keepAlive {
+			// eat messages until keep alive channel closes
+		}
+	}()
+
+	return s, nil
+}
+
+// Lease is the lease ID for keys bound to the session.
+func (s *Session) Lease() lease.LeaseID { return s.id }
+
+// Done returns a channel that closes when the lease is orphaned, expires, or
+// is otherwise no longer being refreshed.
+func (s *Session) Done() <-chan struct{} { return s.donec }
+
+// Orphan ends the refresh for the session lease. This is useful
+// in case the state of the client connection is indeterminate (revoke
+// would fail) or when transferring lease ownership.
+func (s *Session) Orphan() {
+	s.cancel()
+	<-s.donec
+}
+
+// Close orphans the session and revokes the session lease.
+func (s *Session) Close() error {
+	s.Orphan()
+	_, err := v3.NewLease(s.client).Revoke(context.TODO(), s.id)
+	return err
+}

clientv3/mirror/syncer.go

@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-package sync
+package mirror
 
 import (
 	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"

clientv3/op.go

@@ -227,3 +227,26 @@ func WithFromKey() OpOption { return WithRange("\x00") }
 func WithSerializable() OpOption {
 	return func(op *Op) { op.serializable = true }
 }
+
+// WithFirstCreate gets the key with the oldest creation revision in the request range.
+func WithFirstCreate() []OpOption { return withTop(SortByCreatedRev, SortAscend) }
+
+// WithLastCreate gets the key with the latest creation revision in the request range.
+func WithLastCreate() []OpOption { return withTop(SortByCreatedRev, SortDescend) }
+
+// WithFirstKey gets the lexically first key in the request range.
+func WithFirstKey() []OpOption { return withTop(SortByKey, SortAscend) }
+
+// WithLastKey gets the lexically last key in the request range.
+func WithLastKey() []OpOption { return withTop(SortByKey, SortDescend) }
+
+// WithFirstRev gets the key with the oldest modification revision in the request range.
+func WithFirstRev() []OpOption { return withTop(SortByModifiedRev, SortAscend) }
+
+// WithLastRev gets the key with the latest modification revision in the request range.
+func WithLastRev() []OpOption { return withTop(SortByModifiedRev, SortDescend) }
+
+// withTop gets the first key over the get's prefix given a sort order
+func withTop(target SortTarget, order SortOrder) []OpOption {
+	return []OpOption{WithPrefix(), WithSort(target, order), WithLimit(1)}
+}

contrib/recipes/barrier.go

@@ -49,7 +49,7 @@ func (b *Barrier) Release() error {
 // Wait blocks on the barrier key until it is deleted. If there is no key, Wait
 // assumes Release has already been called and returns immediately.
 func (b *Barrier) Wait() error {
-	resp, err := b.kv.Get(b.ctx, b.key, withFirstKey()...)
+	resp, err := b.kv.Get(b.ctx, b.key, v3.WithFirstKey()...)
 	if err != nil {
 		return err
 	}

contrib/recipes/election.go

@@ -62,7 +62,7 @@ func (e *Election) Resign() (err error) {
 
 // Leader returns the leader value for the current election.
 func (e *Election) Leader() (string, error) {
-	resp, err := e.kv.Get(e.ctx, e.keyPrefix, withFirstCreate()...)
+	resp, err := e.kv.Get(e.ctx, e.keyPrefix, v3.WithFirstCreate()...)
 	if err != nil {
 		return "", err
 	} else if len(resp.Kvs) == 0 {
@@ -74,7 +74,7 @@ func (e *Election) Leader() (string, error) {
 
 // Wait waits for a leader to be elected, returning the leader value.
 func (e *Election) Wait() (string, error) {
-	resp, err := e.kv.Get(e.ctx, e.keyPrefix, withFirstCreate()...)
+	resp, err := e.kv.Get(e.ctx, e.keyPrefix, v3.WithFirstCreate()...)
 	if err != nil {
 		return "", err
 	} else if len(resp.Kvs) != 0 {
@@ -93,7 +93,7 @@ func (e *Election) Wait() (string, error) {
 }
 
 func (e *Election) waitLeadership(tryKey *EphemeralKV) error {
-	opts := append(withLastCreate(), v3.WithRev(tryKey.Revision()-1))
+	opts := append(v3.WithLastCreate(), v3.WithRev(tryKey.Revision()-1))
 	resp, err := e.kv.Get(e.ctx, e.keyPrefix, opts...)
 	if err != nil {
 		return err

contrib/recipes/key.go

@@ -21,6 +21,7 @@ import (
 
 	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
 	v3 "github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
 	"github.com/coreos/etcd/lease"
 )
 
@@ -98,7 +99,7 @@ func NewSequentialKV(kv v3.KV, prefix, val string) (*RemoteKV, error) {
 // newSequentialKV allocates a new sequential key <prefix>/nnnnn with a given
 // value and lease.  Note: a bookkeeping node __<prefix> is also allocated.
 func newSequentialKV(kv v3.KV, prefix, val string, leaseID lease.LeaseID) (*RemoteKV, error) {
-	resp, err := kv.Get(context.TODO(), prefix, withLastKey()...)
+	resp, err := kv.Get(context.TODO(), prefix, v3.WithLastKey()...)
 	if err != nil {
 		return nil, err
 	}
@@ -161,11 +162,11 @@ type EphemeralKV struct{ RemoteKV }
 
 // NewEphemeralKV creates a new key/value pair associated with a session lease
 func NewEphemeralKV(client *v3.Client, key, val string) (*EphemeralKV, error) {
-	leaseID, err := SessionLease(client)
+	s, err := concurrency.NewSession(client)
 	if err != nil {
 		return nil, err
 	}
-	k, err := NewKV(v3.NewKV(client), key, val, leaseID)
+	k, err := NewKV(v3.NewKV(client), key, val, s.Lease())
 	if err != nil {
 		return nil, err
 	}

contrib/recipes/lease.go

@@ -1,113 +0,0 @@
-// Copyright 2016 CoreOS, Inc.
-//
-// 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 recipe
-
-import (
-	"sync"
-
-	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
-	"github.com/coreos/etcd/clientv3"
-	"github.com/coreos/etcd/lease"
-)
-
-// only keep one ephemeral lease per client
-var clientLeases clientLeaseMgr = clientLeaseMgr{leases: make(map[*clientv3.Client]*leaseKeepAlive)}
-
-type clientLeaseMgr struct {
-	leases map[*clientv3.Client]*leaseKeepAlive
-	mu     sync.Mutex
-}
-
-type leaseKeepAlive struct {
-	id     lease.LeaseID
-	cancel context.CancelFunc
-	donec  <-chan struct{}
-}
-
-func SessionLease(client *clientv3.Client) (lease.LeaseID, error) {
-	return clientLeases.sessionLease(client, 120)
-}
-
-func SessionLeaseTTL(client *clientv3.Client, ttl int64) (lease.LeaseID, error) {
-	return clientLeases.sessionLease(client, ttl)
-}
-
-// StopSessionLease ends the refresh for the session lease. This is useful
-// in case the state of the client connection is indeterminate (revoke
-// would fail) or if transferring lease ownership.
-func StopSessionLease(client *clientv3.Client) {
-	clientLeases.mu.Lock()
-	lka := clientLeases.leases[client]
-	clientLeases.mu.Unlock()
-	if lka != nil {
-		lka.cancel()
-		<-lka.donec
-	}
-}
-
-// RevokeSessionLease revokes the session lease.
-func RevokeSessionLease(client *clientv3.Client) (err error) {
-	clientLeases.mu.Lock()
-	lka := clientLeases.leases[client]
-	clientLeases.mu.Unlock()
-	StopSessionLease(client)
-	if lka != nil {
-		_, err = clientv3.NewLease(client).Revoke(context.TODO(), lka.id)
-	}
-	return err
-}
-
-func (clm *clientLeaseMgr) sessionLease(client *clientv3.Client, ttl int64) (lease.LeaseID, error) {
-	clm.mu.Lock()
-	defer clm.mu.Unlock()
-	if lka, ok := clm.leases[client]; ok {
-		return lka.id, nil
-	}
-
-	lc := clientv3.NewLease(client)
-	resp, err := lc.Create(context.TODO(), ttl)
-	if err != nil {
-		return lease.NoLease, err
-	}
-	id := lease.LeaseID(resp.ID)
-
-	ctx, cancel := context.WithCancel(context.Background())
-	keepAlive, err := lc.KeepAlive(ctx, id)
-	if err != nil || keepAlive == nil {
-		return lease.NoLease, err
-	}
-
-	donec := make(chan struct{})
-	lka := &leaseKeepAlive{
-		id:     id,
-		cancel: cancel,
-		donec:  donec}
-	clm.leases[client] = lka
-
-	// keep the lease alive until client error or cancelled context
-	go func() {
-		defer func() {
-			clm.mu.Lock()
-			delete(clm.leases, client)
-			clm.mu.Unlock()
-			lc.Close()
-			close(donec)
-		}()
-		for range keepAlive {
-			// eat messages until keep alive channel closes
-		}
-	}()
-
-	return id, nil
-}

contrib/recipes/mutex.go

@@ -1,91 +0,0 @@
-// Copyright 2016 CoreOS, Inc.
-//
-// 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 recipe
-
-import (
-	"sync"
-
-	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
-	v3 "github.com/coreos/etcd/clientv3"
-	"github.com/coreos/etcd/storage/storagepb"
-)
-
-// Mutex implements the sync Locker interface with etcd
-type Mutex struct {
-	client *v3.Client
-	kv     v3.KV
-	ctx    context.Context
-
-	key   string
-	myKey *EphemeralKV
-}
-
-func NewMutex(client *v3.Client, key string) *Mutex {
-	return &Mutex{client, v3.NewKV(client), context.TODO(), key, nil}
-}
-
-func (m *Mutex) Lock() (err error) {
-	// put self in lock waiters via myKey; oldest waiter holds lock
-	m.myKey, err = NewUniqueEphemeralKey(m.client, m.key)
-	if err != nil {
-		return err
-	}
-	// find oldest element in waiters via revision of insertion
-	resp, err := m.kv.Get(m.ctx, m.key, withFirstRev()...)
-	if err != nil {
-		return err
-	}
-	// if myKey is oldest in waiters, then myKey holds the lock
-	if m.myKey.Revision() == resp.Kvs[0].CreateRevision {
-		return nil
-	}
-	// otherwise myKey isn't lowest, so there must be a key prior to myKey
-	opts := append(withLastRev(), v3.WithRev(m.myKey.Revision()-1))
-	lastKey, err := m.kv.Get(m.ctx, m.key, opts...)
-	if err != nil {
-		return err
-	}
-	// wait for release on prior key
-	_, err = WaitEvents(
-		m.client,
-		string(lastKey.Kvs[0].Key),
-		m.myKey.Revision()-1,
-		[]storagepb.Event_EventType{storagepb.DELETE})
-	// myKey now oldest
-	return err
-}
-
-func (m *Mutex) Unlock() error {
-	err := m.myKey.Delete()
-	m.myKey = nil
-	return err
-}
-
-type lockerMutex struct{ *Mutex }
-
-func (lm *lockerMutex) Lock() {
-	if err := lm.Mutex.Lock(); err != nil {
-		panic(err)
-	}
-}
-func (lm *lockerMutex) Unlock() {
-	if err := lm.Mutex.Unlock(); err != nil {
-		panic(err)
-	}
-}
-
-func NewLocker(client *v3.Client, key string) sync.Locker {
-	return &lockerMutex{NewMutex(client, key)}
-}

contrib/recipes/priority_queue.go

@@ -46,7 +46,7 @@ func (q *PriorityQueue) Enqueue(val string, pr uint16) error {
 // queue is empty, Dequeue blocks until items are available.
 func (q *PriorityQueue) Dequeue() (string, error) {
 	// TODO: fewer round trips by fetching more than one key
-	resp, err := q.kv.Get(q.ctx, q.key, withFirstKey()...)
+	resp, err := q.kv.Get(q.ctx, q.key, v3.WithFirstKey()...)
 	if err != nil {
 		return "", err
 	}

contrib/recipes/queue.go

@@ -42,7 +42,7 @@ func (q *Queue) Enqueue(val string) error {
 // queue is empty, Dequeue blocks until elements are available.
 func (q *Queue) Dequeue() (string, error) {
 	// TODO: fewer round trips by fetching more than one key
-	resp, err := q.kv.Get(q.ctx, q.keyPrefix, withFirstRev()...)
+	resp, err := q.kv.Get(q.ctx, q.keyPrefix, v3.WithFirstRev()...)
 	if err != nil {
 		return "", err
 	}

contrib/recipes/range.go

@@ -1,34 +0,0 @@
-// Copyright 2016 CoreOS, Inc.
-//
-// 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 recipe
-
-import (
-	v3 "github.com/coreos/etcd/clientv3"
-)
-
-func withFirstCreate() []v3.OpOption { return withTop(v3.SortByCreatedRev, v3.SortAscend) }
-func withLastCreate() []v3.OpOption  { return withTop(v3.SortByCreatedRev, v3.SortDescend) }
-func withFirstKey() []v3.OpOption    { return withTop(v3.SortByKey, v3.SortAscend) }
-func withLastKey() []v3.OpOption     { return withTop(v3.SortByKey, v3.SortDescend) }
-func withFirstRev() []v3.OpOption    { return withTop(v3.SortByModifiedRev, v3.SortAscend) }
-func withLastRev() []v3.OpOption     { return withTop(v3.SortByModifiedRev, v3.SortDescend) }
-
-// withTop gets the first key over the get's prefix given a sort order
-func withTop(target v3.SortTarget, order v3.SortOrder) []v3.OpOption {
-	return []v3.OpOption{
-		v3.WithPrefix(),
-		v3.WithSort(target, order),
-		v3.WithLimit(1)}
-}

contrib/recipes/rwmutex.go

@@ -42,7 +42,7 @@ func (rwm *RWMutex) RLock() error {
 
 	// if there are nodes with "write-" and a lower
 	// revision number than us we must wait
-	resp, err := rwm.kv.Get(rwm.ctx, rwm.key+"/write", withFirstRev()...)
+	resp, err := rwm.kv.Get(rwm.ctx, rwm.key+"/write", v3.WithFirstRev()...)
 	if err != nil {
 		return err
 	}
@@ -62,7 +62,7 @@ func (rwm *RWMutex) Lock() error {
 
 	for {
 		// find any key of lower rev number blocks the write lock
-		opts := append(withLastRev(), v3.WithRev(rk.Revision()-1))
+		opts := append(v3.WithLastRev(), v3.WithRev(rk.Revision()-1))
 		resp, err := rwm.kv.Get(rwm.ctx, rwm.key, opts...)
 		if err != nil {
 			return err
@@ -82,7 +82,7 @@ func (rwm *RWMutex) Lock() error {
 
 func (rwm *RWMutex) waitOnLowest() error {
 	// must block; get key before ek for waiting
-	opts := append(withLastRev(), v3.WithRev(rwm.myKey.Revision()-1))
+	opts := append(v3.WithLastRev(), v3.WithRev(rwm.myKey.Revision()-1))
 	lastKey, err := rwm.kv.Get(rwm.ctx, rwm.key, opts...)
 	if err != nil {
 		return err

etcdctlv3/README.md

@@ -264,6 +264,25 @@ bar
 
 ## Utility Commands
 
+### LOCK \<lockname\>
+
+LOCK acquires a distributed named mutex with a given name. Once the lock is acquired, it will be held until etcdctlv3 is terminated.
+
+#### Return value
+
+- Once the lock is acquired, the result for the GET on the unique lock holder key is displayed.
+
+- LOCK returns a zero exit code only if it is terminated by a signal and can release the lock.
+
+#### Example
+```bash
+./etcdctl lock mylock
+mylock/1234534535445
+
+
+```
+
+
 ### MAKE-MIRROR [options] \<destination\>
 
 [make-mirror][mirror] mirrors a key prefix in an etcd cluster to a destination etcd cluster.

etcdctlv3/command/lock_command.go

@@ -0,0 +1,88 @@
+// Copyright 2016 CoreOS, Inc.
+//
+// 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 command
+
+import (
+	"errors"
+	"os"
+	"os/signal"
+
+	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/spf13/cobra"
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
+	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
+)
+
+// NewLockCommand returns the cobra command for "lock".
+func NewLockCommand() *cobra.Command {
+	c := &cobra.Command{
+		Use:   "lock <lockname>",
+		Short: "lock acquires a named lock",
+		Run:   lockCommandFunc,
+	}
+	return c
+}
+
+func lockCommandFunc(cmd *cobra.Command, args []string) {
+	if len(args) != 1 {
+		ExitWithError(ExitBadArgs, errors.New("lock takes one lock name arguement."))
+	}
+	c := mustClientFromCmd(cmd)
+	if err := lockUntilSignal(c, args[0]); err != nil {
+		ExitWithError(ExitError, err)
+	}
+}
+
+func lockUntilSignal(c *clientv3.Client, lockname string) error {
+	m := concurrency.NewMutex(context.TODO(), c, lockname)
+	ctx, cancel := context.WithCancel(context.TODO())
+
+	// unlock in case of ordinary shutdown
+	donec := make(chan struct{})
+	sigc := make(chan os.Signal, 1)
+	signal.Notify(sigc, os.Interrupt, os.Kill)
+	go func() {
+		<-sigc
+		cancel()
+		close(donec)
+	}()
+
+	s, serr := concurrency.NewSession(c)
+	if serr != nil {
+		return serr
+	}
+
+	if err := m.Lock(ctx); err != nil {
+		return err
+	}
+
+	k, kerr := clientv3.NewKV(c).Get(ctx, m.Key())
+	if kerr != nil {
+		return kerr
+	}
+	if len(k.Kvs) == 0 {
+		return errors.New("lock lost on init")
+	}
+
+	display.Get(*k)
+
+	select {
+	case <-donec:
+		return m.Unlock()
+	case <-s.Done():
+	}
+
+	return errors.New("session expired")
+}

etcdctlv3/command/make_mirror_command.go

@@ -23,7 +23,7 @@ import (
 	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/spf13/cobra"
 	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
 	"github.com/coreos/etcd/clientv3"
-	"github.com/coreos/etcd/clientv3/sync"
+	"github.com/coreos/etcd/clientv3/mirror"
 	"github.com/coreos/etcd/etcdserver/api/v3rpc"
 	"github.com/coreos/etcd/storage/storagepb"
 )
@@ -77,7 +77,7 @@ func makeMirror(ctx context.Context, c *clientv3.Client, dc *clientv3.Client) er
 	// TODO: remove the prefix of the destination cluster?
 	dkv := clientv3.NewKV(dc)
 
-	s := sync.NewSyncer(c, mmprefix, 0)
+	s := mirror.NewSyncer(c, mmprefix, 0)
 
 	rc, errc := s.SyncBase(ctx)
 

etcdctlv3/command/snapshot_command.go

@@ -22,7 +22,7 @@ import (
 	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/spf13/cobra"
 	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
 	"github.com/coreos/etcd/clientv3"
-	"github.com/coreos/etcd/clientv3/sync"
+	"github.com/coreos/etcd/clientv3/mirror"
 	"github.com/coreos/etcd/etcdserver/api/v3rpc"
 )
 
@@ -90,7 +90,7 @@ func snapshotToFile(c *clientv3.Client, path string) {
 // snapshot reads all of a watcher; returns compaction revision if incomplete
 // TODO: stabilize snapshot format
 func snapshot(w io.Writer, c *clientv3.Client, rev int64) int64 {
-	s := sync.NewSyncer(c, "", rev)
+	s := mirror.NewSyncer(c, "", rev)
 
 	rc, errc := s.SyncBase(context.TODO())
 

etcdctlv3/main.go

@@ -62,6 +62,7 @@ func init() {
 		command.NewMemberCommand(),
 		command.NewSnapshotCommand(),
 		command.NewMakeMirrorCommand(),
+		command.NewLockCommand(),
 	)
 }
 

integration/v3_double_barrier_test.go

@@ -17,13 +17,14 @@ import (
 	"testing"
 	"time"
 
+	"github.com/coreos/etcd/clientv3/concurrency"
 	"github.com/coreos/etcd/contrib/recipes"
 )
 
 func TestDoubleBarrier(t *testing.T) {
 	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
 	defer clus.Terminate(t)
-	defer closeSessionLease(clus)
+	defer dropSessionLease(clus)
 
 	waiters := 10
 
@@ -84,7 +85,7 @@ func TestDoubleBarrier(t *testing.T) {
 func TestDoubleBarrierFailover(t *testing.T) {
 	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
 	defer clus.Terminate(t)
-	defer closeSessionLease(clus)
+	defer dropSessionLease(clus)
 
 	waiters := 10
 	donec := make(chan struct{})
@@ -119,7 +120,13 @@ func TestDoubleBarrierFailover(t *testing.T) {
 		}
 	}
 	// kill lease, expect Leave unblock
-	recipe.RevokeSessionLease(clus.clients[0])
+	s, err := concurrency.NewSession(clus.clients[0])
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err = s.Close(); err != nil {
+		t.Fatal(err)
+	}
 	// join on rest of waiters
 	for i := 0; i < waiters-1; i++ {
 		select {
@@ -130,8 +137,9 @@ func TestDoubleBarrierFailover(t *testing.T) {
 	}
 }
 
-func closeSessionLease(clus *ClusterV3) {
+func dropSessionLease(clus *ClusterV3) {
 	for _, client := range clus.clients {
-		recipe.StopSessionLease(client)
+		s, _ := concurrency.NewSession(client)
+		s.Orphan()
 	}
 }

integration/v3_election_test.go

@@ -18,6 +18,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/coreos/etcd/clientv3/concurrency"
 	"github.com/coreos/etcd/contrib/recipes"
 )
 
@@ -25,7 +26,7 @@ import (
 func TestElectionWait(t *testing.T) {
 	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
 	defer clus.Terminate(t)
-	defer closeSessionLease(clus)
+	defer dropSessionLease(clus)
 
 	leaders := 3
 	followers := 3
@@ -88,7 +89,7 @@ func TestElectionWait(t *testing.T) {
 func TestElectionFailover(t *testing.T) {
 	clus := NewClusterV3(t, &ClusterConfig{Size: 3})
 	defer clus.Terminate(t)
-	defer closeSessionLease(clus)
+	defer dropSessionLease(clus)
 
 	// first leader (elected)
 	e := recipe.NewElection(clus.clients[0], "test-election")
@@ -116,7 +117,11 @@ func TestElectionFailover(t *testing.T) {
 	}()
 
 	// invoke leader failover
-	err = recipe.RevokeSessionLease(clus.clients[0])
+	session, serr := concurrency.NewSession(clus.clients[0])
+	if serr != nil {
+		t.Fatal(serr)
+	}
+	err = session.Close()
 	if err != nil {
 		t.Fatal(err)
 	}

integration/v3_lock_test.go

@@ -18,7 +18,9 @@ import (
 	"testing"
 	"time"
 
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/context"
 	"github.com/coreos/etcd/clientv3"
+	"github.com/coreos/etcd/clientv3/concurrency"
 	"github.com/coreos/etcd/contrib/recipes"
 )
 
@@ -36,11 +38,11 @@ func TestMutexMultiNode(t *testing.T) {
 
 func testMutex(t *testing.T, waiters int, chooseClient func() *clientv3.Client) {
 	// stream lock acquisitions
-	lockedC := make(chan *recipe.Mutex, 1)
+	lockedC := make(chan *concurrency.Mutex, 1)
 	for i := 0; i < waiters; i++ {
 		go func() {
-			m := recipe.NewMutex(chooseClient(), "test-mutex")
-			if err := m.Lock(); err != nil {
+			m := concurrency.NewMutex(context.TODO(), chooseClient(), "test-mutex")
+			if err := m.Lock(context.TODO()); err != nil {
 				t.Fatalf("could not wait on lock (%v)", err)
 			}
 			lockedC <- m