package concurrency
import (
"fmt"
"sync"
v3 "github.com/coreos/etcd/clientv3"
"golang.org/x/net/context"
)
// Mutex implements the sync Locker interface with etcd
type Mutex struct { s *Session
pfx string
myKey string
myRev int64
}
func NewMutex(s *Session, pfx string) *Mutex { return &Mutex{s, 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 := m.s
client := m.s.Client()
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 := 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, client, m.pfx, m.myRev-1)
// release lock key if cancelled
select { case <-ctx.Done():
m.Unlock(client.Ctx())
default:
}
return err
}
func (m *Mutex) Unlock(ctx context.Context) error { client := m.s.Client()
if _, err := client.Delete(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.CreateRevision(m.myKey), "=", m.myRev)
}
func (m *Mutex) Key() string { return m.myKey }
type lockerMutex struct{ *Mutex }
func (lm *lockerMutex) Lock() { client := lm.s.Client()
if err := lm.Mutex.Lock(client.Ctx()); err != nil { panic(err)
}
}
func (lm *lockerMutex) Unlock() { client := lm.s.Client()
if err := lm.Mutex.Unlock(client.Ctx()); err != nil { panic(err)
}
}
// NewLocker creates a sync.Locker backed by an etcd mutex.
func NewLocker(s *Session, pfx string) sync.Locker { return &lockerMutex{NewMutex(s, pfx)}}