Docker's observer pattern Subscribe/publisher implementation

Some data pushes need to be in observer mode (also known as subscriber mode) to see how Docker implements this with Golang

Over the data structure type Events struct {mu sync. Mutex//Lock events []*jsonmessage. Jsonmessage//Data pub *pubsub. Publisher//Publisher}type publisher struct {m sync. Rwmutex buffer int//buffer timeout time. Duration//Timeout subscribers map[subscriber]struct{}//Subscriber map structure for easy traversal of map}

As a subscriber, subscribe once

Func (e *events) Subscribe () ([]*jsonmessage. Jsonmessage, Chan interface{}) {E.mu.lock () Current: = Make ([]*jsonmessage. Jsonmessage, Len (e.events))//e.events be notified when the Subscriber copy (current, e.events) L: = E.pub.subscribe ()//subscription, Log in to Publisher's subscribers to E.mu.unlock () return current, L}func (P *publisher) Subscribe () Chan interface{} {ch: = make ( Chan interface{}, P.buffer) P.m.lock () p.subscribers[ch] = struct{}{}//Record P.m.unlock () return CH//return to a pipeline}

Generate publisher once, of course, to broadcast to all subscribers.

Func (e *events) Log (action, ID, from string) {go func () {E.mu.lock () JM: = &jsonmessage. Jsonmessage{status:action, Id:id, From:from, Time:time. Now (). UTC (). Unix ()}if len (e.events) = = Cap (e.events) {//discards the oldest record because the size exceeds the allocated copy (E.events, e.events[1:]) E.events[len (e.events)- 1] = JM} else {e.events = append (e.events, JM)}e.mu.unlock () e.pub.publish (JM)//Publish Broadcast} ()}

And finally look at the broadcast code.

Func (P *publisher) Publish (v interface{}) {P.m.rlock () for sub: = Range p.subscribers {//Send under a select as to not BL Ock If the receiver is unavailable//if the setting times out, the default setting is 100*time. Millisecond, the data is sent, if it is not sent, it is blocked until you receive the timeout message if p.timeout > 0 {select {case sub <-v:case <-time. After (p.timeout):}continue}//does not set a time-out, the data is not sent to the pipeline successfully, then the default continues to execute Select {case Sub <-V:default:}}p.m.runlock ()}

See where we got this data:

//............ Omit for {select {case EV: = <-l://To the subscriber's outgoing data Jev to the pipeline, OK: = ev. ( *jsonmessage. Jsonmessage) If!ok {continue}if err: = Sendevent (JEV); Err! = Nil {return err}case <-timer. C://takes the timeout information to return nilcase <-closenotify://to the close notification message Logrus. Debug ("Client disconnected, stop sending events") return nil}}

Docker's observer pattern Subscribe/publisher implementation