// Reserve will reserve an item with the id in the DefaultReservation for the given amount of
// time.
func (dr *DefaultReservation) Reserve(d time.Duration) error {
log.Debugf("[Sync:Reservation] Attempting to reserve '%s' for %s...", dr.id, d)
lockpath := constructPath(dr.path, dr.id)
// Check if the reservation already exists
b, _, err := zookeeper.Get(lockpath)
if err == nil {
// It exists, check if expired
var expired time.Time
expired.GobDecode(b)
log.Debugf("[Sync:Reservation] Read existing node for '%s', expires at %s", dr.id, expired)
if expired.Before(time.Now()) {
log.Debugf("[Sync:Reservation] Deleting expired lock '%s'", dr.id)
// It has expired, delete the node and get the reservation as usual
zookeeper.Delete(lockpath, -1)
} else {
return ErrReserved
}
}
expires := time.Now().Add(d)
expiresBytes, err := expires.GobEncode()
if err != nil {
return err
}
for {
_, err = zookeeper.Create(lockpath, expiresBytes, 0, dr.acl)
if err == gozk.ErrNoNode {
createParents(dr.path)
} else if err == nil {
break
} else {
log.Warnf("[Reservation] ZK error creating ephemeral lock node for reservation: %v", err)
return err
}
}
log.Debugf("[Sync:Reservation] Created lock node for '%s', expires at %s", dr.id, expires)
return nil
}
// findLowestSequenceNode within a particular lock path
func findLowestSequenceNode(path string, seq int) (lowestSeq int, prevSeqPath string, err error) {
// Read all the children of the node
// This is why we create sequential nodes under a parent node based on the lock ID
// If not, say we stored all ephemeral locks under a higher level parent,
// we would be checking nodes of every lock currently in play, rather than locks
// on this ID
children, _, err := zookeeper.Children(path)
if err != nil {
return -1, "", err
}
var ttl time.Time
lowestSeq = seq
prevSeq := 0
prevSeqPath = ""
for _, p := range children {
// Check if this lock has timed out
data, _, _ := zookeeper.Get(path + "/" + p)
if len(data) > 0 {
ttl.GobDecode(data)
if ttl.Before(time.Now()) {
log.Tracef("[RegionLock] Deleting expired lock '%s'", path+"/"+p)
zookeeper.Delete(path+"/"+p, -1)
continue
}
}
s, err := parseSeq(p)
if err != nil {
return -1, "", err
}
if s < lowestSeq {
lowestSeq = s
}
if s < seq && s > prevSeq {
prevSeq = s
prevSeqPath = p
}
}
return lowestSeq, prevSeqPath, err
}