// 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, serr := NewSession(m.client)
if serr != nil {
return serr
}
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)
resp, err := m.client.Txn(ctx).If(cmp).Then(put).Else(get).Commit()
if err != nil {
return err
}
m.myRev = resp.Header.Revision
if !resp.Succeeded {
m.myRev = resp.Responses[0].GetResponseRange().Kvs[0].CreateRevision
}
// wait for deletion revisions prior to myKey
err = waitDeletes(ctx, m.client, m.pfx, v3.WithPrefix(), v3.WithRev(m.myRev-1))
// release lock key if cancelled
select {
case <-ctx.Done():
m.Unlock()
default:
}
return err
}
func parseCompare(line string) (*clientv3.Cmp, error) {
var (
key string
op string
val string
)
lparenSplit := strings.SplitN(line, "(", 2)
if len(lparenSplit) != 2 {
return nil, fmt.Errorf("malformed comparison: %s", line)
}
target := lparenSplit[0]
n, serr := fmt.Sscanf(lparenSplit[1], "%q) %s %q", &key, &op, &val)
if n != 3 {
return nil, fmt.Errorf("malformed comparison: %s; got %s(%q) %s %q", line, target, key, op, val)
}
if serr != nil {
return nil, fmt.Errorf("malformed comparison: %s (%v)", line, serr)
}
var (
v int64
err error
cmp clientv3.Cmp
)
switch target {
case "ver", "version":
if v, err = strconv.ParseInt(val, 10, 64); err == nil {
cmp = clientv3.Compare(clientv3.Version(key), op, v)
}
case "c", "create":
if v, err = strconv.ParseInt(val, 10, 64); err == nil {
cmp = clientv3.Compare(clientv3.CreateRevision(key), op, v)
}
case "m", "mod":
if v, err = strconv.ParseInt(val, 10, 64); err == nil {
cmp = clientv3.Compare(clientv3.ModRevision(key), op, v)
}
case "val", "value":
cmp = clientv3.Compare(clientv3.Value(key), op, val)
default:
return nil, fmt.Errorf("malformed comparison: %s (unknown target %s)", line, target)
}
if err != nil {
return nil, fmt.Errorf("invalid txn compare request: %s", line)
}
return &cmp, nil
}
// Lock locks resources on sync
// This call blocks until you can get lock
func (s *Sync) Lock(path string, block bool) error {
for {
if s.HasLock(path) {
return nil
}
var err error
lease, err := s.etcdClient.Grant(s.withTimeout(), masterTTL)
var resp *etcd.TxnResponse
if err == nil {
cmp := etcd.Compare(etcd.CreateRevision(path), "=", 0)
put := etcd.OpPut(path, s.processID, etcd.WithLease(lease.ID))
resp, err = s.etcdClient.Txn(s.withTimeout()).If(cmp).Then(put).Commit()
}
if err != nil || !resp.Succeeded {
msg := fmt.Sprintf("failed to lock path %s", path)
if err != nil {
msg = fmt.Sprintf("failed to lock path %s: %s", path, err)
}
log.Notice(msg)
s.locks.Remove(path)
if !block {
return errors.New(msg)
}
time.Sleep(masterTTL * time.Second)
continue
}
log.Info("Locked %s", path)
s.locks.Set(path, lease.ID)
//Refresh master token
go func() {
defer func() {
log.Notice("releasing keepalive lock for %s", path)
s.locks.Remove(path)
}()
for s.HasLock(path) {
ch, err := s.etcdClient.KeepAlive(s.withTimeout(), lease.ID)
if err != nil {
log.Notice("failed to keepalive lock for %s %s", path, err)
return
}
for range ch {
}
}
}()
return nil
}
}
// Proclaim lets the leader announce a new value without another election.
func (e *Election) Proclaim(ctx context.Context, val string) error {
if e.leaderSession == nil {
return ErrElectionNotLeader
}
cmp := v3.Compare(v3.CreateRevision(e.leaderKey), "=", e.leaderRev)
txn := e.client.Txn(ctx).If(cmp)
txn = txn.Then(v3.OpPut(e.leaderKey, val, v3.WithLease(e.leaderSession.Lease())))
tresp, terr := txn.Commit()
if terr != nil {
return terr
}
if !tresp.Succeeded {
e.leaderKey = ""
return ErrElectionNotLeader
}
return nil
}
// Campaign puts a value as eligible for the election. It blocks until
// it is elected, an error occurs, or the context is cancelled.
func (e *Election) Campaign(ctx context.Context, val string) error {
s, serr := NewSession(e.client)
if serr != nil {
return serr
}
k := fmt.Sprintf("%s/%x", e.keyPrefix, s.Lease())
txn := e.client.Txn(ctx).If(v3.Compare(v3.CreateRevision(k), "=", 0))
txn = txn.Then(v3.OpPut(k, val, v3.WithLease(s.Lease())))
txn = txn.Else(v3.OpGet(k))
resp, err := txn.Commit()
if err != nil {
return err
}
e.leaderKey, e.leaderRev, e.leaderSession = k, resp.Header.Revision, s
if !resp.Succeeded {
kv := resp.Responses[0].GetResponseRange().Kvs[0]
e.leaderRev = kv.CreateRevision
if string(kv.Value) != val {
if err = e.Proclaim(ctx, val); err != nil {
e.Resign(ctx)
return err
}
}
}
err = waitDeletes(ctx, e.client, e.keyPrefix, v3.WithPrefix(), v3.WithRev(e.leaderRev-1))
if err != nil {
// clean up in case of context cancel
select {
case <-ctx.Done():
e.Resign(e.client.Ctx())
default:
e.leaderSession = nil
}
return err
}
return nil
}
func (m *Mutex) IsOwner() v3.Cmp {
return v3.Compare(v3.CreateRevision(m.myKey), "=", m.myRev)
}