package raft import ( "sync/atomic" ) // Observation is sent along the given channel to observers when an event occurs. type Observation struct { // Raft holds the Raft instance generating the observation. Raft *Raft // Data holds observation-specific data. Possible types are // *RequestVoteRequest and RaftState. Data interface{} } // nextObserverId is used to provide a unique ID for each observer to aid in // deregistration. var nextObserverID uint64 // FilterFn is a function that can be registered in order to filter observations. // The function reports whether the observation should be included - if // it returns false, the observation will be filtered out. type FilterFn func(o *Observation) bool // Observer describes what to do with a given observation. type Observer struct { // channel receives observations. channel chan Observation // blocking, if true, will cause Raft to block when sending an observation // to this observer. This should generally be set to false. blocking bool // filter will be called to determine if an observation should be sent to // the channel. filter FilterFn // id is the ID of this observer in the Raft map. id uint64 // numObserved and numDropped are performance counters for this observer. numObserved uint64 numDropped uint64 } // NewObserver creates a new observer that can be registered // to make observations on a Raft instance. Observations // will be sent on the given channel if they satisfy the // given filter. // // If blocking is true, the observer will block when it can't // send on the channel, otherwise it may discard events. func NewObserver(channel chan Observation, blocking bool, filter FilterFn) *Observer { return &Observer{ channel: channel, blocking: blocking, filter: filter, id: atomic.AddUint64(&nextObserverID, 1), } } // GetNumObserved returns the number of observations. func (or *Observer) GetNumObserved() uint64 { return atomic.LoadUint64(&or.numObserved) } // GetNumDropped returns the number of dropped observations due to blocking. func (or *Observer) GetNumDropped() uint64 { return atomic.LoadUint64(&or.numDropped) } // RegisterObserver registers a new observer. func (r *Raft) RegisterObserver(or *Observer) { r.observersLock.Lock() defer r.observersLock.Unlock() r.observers[or.id] = or } // DeregisterObserver deregisters an observer. func (r *Raft) DeregisterObserver(or *Observer) { r.observersLock.Lock() defer r.observersLock.Unlock() delete(r.observers, or.id) } // observe sends an observation to every observer. func (r *Raft) observe(o interface{}) { // In general observers should not block. But in any case this isn't // disastrous as we only hold a read lock, which merely prevents // registration / deregistration of observers. r.observersLock.RLock() defer r.observersLock.RUnlock() for _, or := range r.observers { // It's wasteful to do this in the loop, but for the common case // where there are no observers we won't create any objects. ob := Observation{Raft: r, Data: o} if or.filter != nil && !or.filter(&ob) { continue } if or.channel == nil { continue } if or.blocking { or.channel <- ob atomic.AddUint64(&or.numObserved, 1) } else { select { case or.channel <- ob: atomic.AddUint64(&or.numObserved, 1) default: atomic.AddUint64(&or.numDropped, 1) } } } }