func (md *MasterDetector) detect(f detector.MasterChanged) {
log.V(3).Infoln("detecting children at", currentPath)
detectLoop:
for {
select {
case <-md.Done():
return
default:
}
log.V(3).Infoln("watching children at", currentPath)
path, childrenCh, errCh := md.client.watchChildren(currentPath)
rewatch := false
for {
started := time.Now()
select {
case children := <-childrenCh:
md.childrenChanged(path, children, f)
case err, ok := <-errCh:
// check for a tie first (required for predictability (tests)); the downside of
// doing this is that a listener might get two callbacks back-to-back ("new leader",
// followed by "no leader").
select {
case children := <-childrenCh:
md.childrenChanged(path, children, f)
default:
}
if ok {
log.V(1).Infoln("child watch ended with error, master lost; error was:", err.Error())
} else {
// detector shutdown likely...
log.V(1).Infoln("child watch ended, master lost")
}
select {
case <-md.Done():
return
default:
if md.leaderNode != "" {
log.V(2).Infof("changing leader node from %q -> \"\"", md.leaderNode)
md.leaderNode = ""
f.OnMasterChanged(nil)
}
}
rewatch = true
}
// rate-limit master changes
if elapsed := time.Now().Sub(started); elapsed > 0 {
log.V(2).Infoln("resting before next detection cycle")
select {
case <-md.Done():
return
case <-time.After(md.minDetectorCyclePeriod - elapsed): // noop
}
}
if rewatch {
continue detectLoop
}
}
}
}
func (md *MasterDetector) notifyMasterChanged(path string, list []string, obs detector.MasterChanged) {
// mesos v0.24 writes JSON only, v0.23 writes json and protobuf, v0.22 and prior only write protobuf
topNode, codec := md.selectTopNode(list)
if md.leaderNode == topNode {
log.V(2).Infof("ignoring children-changed event, leader has not changed: %v", path)
return
}
log.V(2).Infof("changing leader node from %q -> %q", md.leaderNode, topNode)
md.leaderNode = topNode
var masterInfo *mesos.MasterInfo
if md.leaderNode != "" {
var err error
if masterInfo, err = codec(path, topNode); err != nil {
log.Errorln(err.Error())
}
}
log.V(2).Infof("detected master info: %+v", masterInfo)
logPanic(func() { obs.OnMasterChanged(masterInfo) })
}