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// Copyright 2015 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 lease
import (
"encoding/binary"
"errors"
"math"
"sort"
"sync"
"sync/atomic"
"time"
"github.com/coreos/etcd/lease/leasepb"
"github.com/coreos/etcd/mvcc/backend"
"github.com/coreos/etcd/pkg/monotime"
)
const (
// NoLease is a special LeaseID representing the absence of a lease.
NoLease = LeaseID(0)
)
var (
leaseBucketName = []byte("lease")
forever = monotime.Time(math.MaxInt64)
ErrNotPrimary = errors.New("not a primary lessor")
ErrLeaseNotFound = errors.New("lease not found")
ErrLeaseExists = errors.New("lease already exists")
)
// TxnDelete is a TxnWrite that only permits deletes. Defined here
// to avoid circular dependency with mvcc.
type TxnDelete interface {
DeleteRange(key, end []byte) (n, rev int64)
End()
}
// RangeDeleter is a TxnDelete constructor.
type RangeDeleter func() TxnDelete
type LeaseID int64
// Lessor owns leases. It can grant, revoke, renew and modify leases for lessee.
type Lessor interface {
// SetRangeDeleter lets the lessor create TxnDeletes to the store.
// Lessor deletes the items in the revoked or expired lease by creating
// new TxnDeletes.
SetRangeDeleter(rd RangeDeleter)
// Grant grants a lease that expires at least after TTL seconds.
Grant(id LeaseID, ttl int64) (*Lease, error)
// Revoke revokes a lease with given ID. The item attached to the
// given lease will be removed. If the ID does not exist, an error
// will be returned.
Revoke(id LeaseID) error
// Attach attaches given leaseItem to the lease with given LeaseID.
// If the lease does not exist, an error will be returned.
Attach(id LeaseID, items []LeaseItem) error
// GetLease returns LeaseID for given item.
// If no lease found, NoLease value will be returned.
GetLease(item LeaseItem) LeaseID
// Detach detaches given leaseItem from the lease with given LeaseID.
// If the lease does not exist, an error will be returned.
Detach(id LeaseID, items []LeaseItem) error
// Promote promotes the lessor to be the primary lessor. Primary lessor manages
// the expiration and renew of leases.
// Newly promoted lessor renew the TTL of all lease to extend + previous TTL.
Promote(extend time.Duration)
// Demote demotes the lessor from being the primary lessor.
Demote()
// Renew renews a lease with given ID. It returns the renewed TTL. If the ID does not exist,
// an error will be returned.
Renew(id LeaseID) (int64, error)
// Lookup gives the lease at a given lease id, if any
Lookup(id LeaseID) *Lease
// ExpiredLeasesC returns a chan that is used to receive expired leases.
ExpiredLeasesC() <-chan []*Lease
// Recover recovers the lessor state from the given backend and RangeDeleter.
Recover(b backend.Backend, rd RangeDeleter)
// Stop stops the lessor for managing leases. The behavior of calling Stop multiple
// times is undefined.
Stop()
}
// lessor implements Lessor interface.
// TODO: use clockwork for testability.
type lessor struct {
mu sync.Mutex
// demotec is set when the lessor is the primary.
// demotec will be closed if the lessor is demoted.
demotec chan struct{}
// TODO: probably this should be a heap with a secondary
// id index.
// Now it is O(N) to loop over the leases to find expired ones.
// We want to make Grant, Revoke, and findExpiredLeases all O(logN) and
// Renew O(1).
// findExpiredLeases and Renew should be the most frequent operations.
leaseMap map[LeaseID]*Lease
itemMap map[LeaseItem]LeaseID
// When a lease expires, the lessor will delete the
// leased range (or key) by the RangeDeleter.
rd RangeDeleter
// backend to persist leases. We only persist lease ID and expiry for now.
// The leased items can be recovered by iterating all the keys in kv.
b backend.Backend
// minLeaseTTL is the minimum lease TTL that can be granted for a lease. Any
// requests for shorter TTLs are extended to the minimum TTL.
minLeaseTTL int64
expiredC chan []*Lease
// stopC is a channel whose closure indicates that the lessor should be stopped.
stopC chan struct{}
// doneC is a channel whose closure indicates that the lessor is stopped.
doneC chan struct{}
}
func NewLessor(b backend.Backend, minLeaseTTL int64) Lessor {
return newLessor(b, minLeaseTTL)
}
func newLessor(b backend.Backend, minLeaseTTL int64) *lessor {
l := &lessor{
leaseMap: make(map[LeaseID]*Lease),
itemMap: make(map[LeaseItem]LeaseID),
b: b,
minLeaseTTL: minLeaseTTL,
// expiredC is a small buffered chan to avoid unnecessary blocking.
expiredC: make(chan []*Lease, 16),
stopC: make(chan struct{}),
doneC: make(chan struct{}),
}
l.initAndRecover()
go l.runLoop()
return l
}
// isPrimary indicates if this lessor is the primary lessor. The primary
// lessor manages lease expiration and renew.
//
// in etcd, raft leader is the primary. Thus there might be two primary
// leaders at the same time (raft allows concurrent leader but with different term)
// for at most a leader election timeout.
// The old primary leader cannot affect the correctness since its proposal has a
// smaller term and will not be committed.
//
// TODO: raft follower do not forward lease management proposals. There might be a
// very small window (within second normally which depends on go scheduling) that
// a raft follow is the primary between the raft leader demotion and lessor demotion.
// Usually this should not be a problem. Lease should not be that sensitive to timing.
func (le *lessor) isPrimary() bool {
return le.demotec != nil
}
func (le *lessor) SetRangeDeleter(rd RangeDeleter) {
le.mu.Lock()
defer le.mu.Unlock()
le.rd = rd
}
func (le *lessor) Grant(id LeaseID, ttl int64) (*Lease, error) {
if id == NoLease {
return nil, ErrLeaseNotFound
}
// TODO: when lessor is under high load, it should give out lease
// with longer TTL to reduce renew load.
l := &Lease{
ID: id,
ttl: ttl,
itemSet: make(map[LeaseItem]struct{}),
revokec: make(chan struct{}),
}
le.mu.Lock()
defer le.mu.Unlock()
if _, ok := le.leaseMap[id]; ok {
return nil, ErrLeaseExists
}
if l.ttl < le.minLeaseTTL {
l.ttl = le.minLeaseTTL
}
if le.isPrimary() {
l.refresh(0)
} else {
l.forever()
}
le.leaseMap[id] = l
l.persistTo(le.b)
return l, nil
}
func (le *lessor) Revoke(id LeaseID) error {
le.mu.Lock()
l := le.leaseMap[id]
if l == nil {
le.mu.Unlock()
return ErrLeaseNotFound
}
defer close(l.revokec)
// unlock before doing external work
le.mu.Unlock()
if le.rd == nil {
return nil
}
txn := le.rd()
// sort keys so deletes are in same order among all members,
// otherwise the backened hashes will be different
keys := l.Keys()
sort.StringSlice(keys).Sort()
for _, key := range keys {
txn.DeleteRange([]byte(key), nil)
}
le.mu.Lock()
defer le.mu.Unlock()
delete(le.leaseMap, l.ID)
// lease deletion needs to be in the same backend transaction with the
// kv deletion. Or we might end up with not executing the revoke or not
// deleting the keys if etcdserver fails in between.
le.b.BatchTx().UnsafeDelete(leaseBucketName, int64ToBytes(int64(l.ID)))
txn.End()
return nil
}
// Renew renews an existing lease. If the given lease does not exist or
// has expired, an error will be returned.
func (le *lessor) Renew(id LeaseID) (int64, error) {
le.mu.Lock()
unlock := func() { le.mu.Unlock() }
defer func() { unlock() }()
if !le.isPrimary() {
// forward renew request to primary instead of returning error.
return -1, ErrNotPrimary
}
demotec := le.demotec
l := le.leaseMap[id]
if l == nil {
return -1, ErrLeaseNotFound
}
if l.expired() {
le.mu.Unlock()
unlock = func() {}
select {
// A expired lease might be pending for revoking or going through
// quorum to be revoked. To be accurate, renew request must wait for the
// deletion to complete.
case <-l.revokec:
return -1, ErrLeaseNotFound
// The expired lease might fail to be revoked if the primary changes.
// The caller will retry on ErrNotPrimary.
case <-demotec:
return -1, ErrNotPrimary
case <-le.stopC:
return -1, ErrNotPrimary
}
}
l.refresh(0)
return l.ttl, nil
}
func (le *lessor) Lookup(id LeaseID) *Lease {
le.mu.Lock()
defer le.mu.Unlock()
return le.leaseMap[id]
}
func (le *lessor) Promote(extend time.Duration) {
le.mu.Lock()
defer le.mu.Unlock()
le.demotec = make(chan struct{})
// refresh the expiries of all leases.
for _, l := range le.leaseMap {
l.refresh(extend)
}
}
func (le *lessor) Demote() {
le.mu.Lock()
defer le.mu.Unlock()
// set the expiries of all leases to forever
for _, l := range le.leaseMap {
l.forever()
}
if le.demotec != nil {
close(le.demotec)
le.demotec = nil
}
}
// Attach attaches items to the lease with given ID. When the lease
// expires, the attached items will be automatically removed.
// If the given lease does not exist, an error will be returned.
func (le *lessor) Attach(id LeaseID, items []LeaseItem) error {
le.mu.Lock()
defer le.mu.Unlock()
l := le.leaseMap[id]
if l == nil {
return ErrLeaseNotFound
}
l.mu.Lock()
for _, it := range items {
l.itemSet[it] = struct{}{}
le.itemMap[it] = id
}
l.mu.Unlock()
return nil
}
func (le *lessor) GetLease(item LeaseItem) LeaseID {
le.mu.Lock()
id := le.itemMap[item]
le.mu.Unlock()
return id
}
// Detach detaches items from the lease with given ID.
// If the given lease does not exist, an error will be returned.
func (le *lessor) Detach(id LeaseID, items []LeaseItem) error {
le.mu.Lock()
defer le.mu.Unlock()
l := le.leaseMap[id]
if l == nil {
return ErrLeaseNotFound
}
l.mu.Lock()
for _, it := range items {
delete(l.itemSet, it)
delete(le.itemMap, it)
}
l.mu.Unlock()
return nil
}
func (le *lessor) Recover(b backend.Backend, rd RangeDeleter) {
le.mu.Lock()
defer le.mu.Unlock()
le.b = b
le.rd = rd
le.leaseMap = make(map[LeaseID]*Lease)
le.itemMap = make(map[LeaseItem]LeaseID)
le.initAndRecover()
}
func (le *lessor) ExpiredLeasesC() <-chan []*Lease {
return le.expiredC
}
func (le *lessor) Stop() {
close(le.stopC)
<-le.doneC
}
func (le *lessor) runLoop() {
defer close(le.doneC)
for {
var ls []*Lease
le.mu.Lock()
if le.isPrimary() {
ls = le.findExpiredLeases()
}
le.mu.Unlock()
if len(ls) != 0 {
select {
case <-le.stopC:
return
case le.expiredC <- ls:
default:
// the receiver of expiredC is probably busy handling
// other stuff
// let's try this next time after 500ms
}
}
select {
case <-time.After(500 * time.Millisecond):
case <-le.stopC:
return
}
}
}
// findExpiredLeases loops all the leases in the leaseMap and returns the expired
// leases that needed to be revoked.
func (le *lessor) findExpiredLeases() []*Lease {
leases := make([]*Lease, 0, 16)
for _, l := range le.leaseMap {
// TODO: probably should change to <= 100-500 millisecond to
// make up committing latency.
if l.expired() {
leases = append(leases, l)
}
}
return leases
}
func (le *lessor) initAndRecover() {
tx := le.b.BatchTx()
tx.Lock()
tx.UnsafeCreateBucket(leaseBucketName)
_, vs := tx.UnsafeRange(leaseBucketName, int64ToBytes(0), int64ToBytes(math.MaxInt64), 0)
// TODO: copy vs and do decoding outside tx lock if lock contention becomes an issue.
for i := range vs {
var lpb leasepb.Lease
err := lpb.Unmarshal(vs[i])
if err != nil {
tx.Unlock()
panic("failed to unmarshal lease proto item")
}
ID := LeaseID(lpb.ID)
if lpb.TTL < le.minLeaseTTL {
lpb.TTL = le.minLeaseTTL
}
le.leaseMap[ID] = &Lease{
ID: ID,
ttl: lpb.TTL,
// itemSet will be filled in when recover key-value pairs
// set expiry to forever, refresh when promoted
itemSet: make(map[LeaseItem]struct{}),
expiry: forever,
revokec: make(chan struct{}),
}
}
tx.Unlock()
le.b.ForceCommit()
}
type Lease struct {
ID LeaseID
ttl int64 // time to live in seconds
// expiry is time when lease should expire; must be 64-bit aligned.
expiry monotime.Time
// mu protects concurrent accesses to itemSet
mu sync.RWMutex
itemSet map[LeaseItem]struct{}
revokec chan struct{}
}
func (l *Lease) expired() bool {
return l.Remaining() <= 0
}
func (l *Lease) persistTo(b backend.Backend) {
key := int64ToBytes(int64(l.ID))
lpb := leasepb.Lease{ID: int64(l.ID), TTL: int64(l.ttl)}
val, err := lpb.Marshal()
if err != nil {
panic("failed to marshal lease proto item")
}
b.BatchTx().Lock()
b.BatchTx().UnsafePut(leaseBucketName, key, val)
b.BatchTx().Unlock()
}
// TTL returns the TTL of the Lease.
func (l *Lease) TTL() int64 {
return l.ttl
}
// refresh refreshes the expiry of the lease.
func (l *Lease) refresh(extend time.Duration) {
t := monotime.Now().Add(extend + time.Duration(l.ttl)*time.Second)
atomic.StoreUint64((*uint64)(&l.expiry), uint64(t))
}
// forever sets the expiry of lease to be forever.
func (l *Lease) forever() { atomic.StoreUint64((*uint64)(&l.expiry), uint64(forever)) }
// Keys returns all the keys attached to the lease.
func (l *Lease) Keys() []string {
l.mu.RLock()
keys := make([]string, 0, len(l.itemSet))
for k := range l.itemSet {
keys = append(keys, k.Key)
}
l.mu.RUnlock()
return keys
}
// Remaining returns the remaining time of the lease.
func (l *Lease) Remaining() time.Duration {
t := monotime.Time(atomic.LoadUint64((*uint64)(&l.expiry)))
return time.Duration(t - monotime.Now())
}
type LeaseItem struct {
Key string
}
func int64ToBytes(n int64) []byte {
bytes := make([]byte, 8)
binary.BigEndian.PutUint64(bytes, uint64(n))
return bytes
}
// FakeLessor is a fake implementation of Lessor interface.
// Used for testing only.
type FakeLessor struct{}
func (fl *FakeLessor) SetRangeDeleter(dr RangeDeleter) {}
func (fl *FakeLessor) Grant(id LeaseID, ttl int64) (*Lease, error) { return nil, nil }
func (fl *FakeLessor) Revoke(id LeaseID) error { return nil }
func (fl *FakeLessor) Attach(id LeaseID, items []LeaseItem) error { return nil }
func (fl *FakeLessor) GetLease(item LeaseItem) LeaseID { return 0 }
func (fl *FakeLessor) Detach(id LeaseID, items []LeaseItem) error { return nil }
func (fl *FakeLessor) Promote(extend time.Duration) {}
func (fl *FakeLessor) Demote() {}
func (fl *FakeLessor) Renew(id LeaseID) (int64, error) { return 10, nil }
func (le *FakeLessor) Lookup(id LeaseID) *Lease { return nil }
func (fl *FakeLessor) ExpiredLeasesC() <-chan []*Lease { return nil }
func (fl *FakeLessor) Recover(b backend.Backend, rd RangeDeleter) {}
func (fl *FakeLessor) Stop() {}
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