ethreact

- consistent renaming
- React -> Event
- ReactorEvent -> EventHandler
- NewReactorEngine -> New
- async ReactorEngine main loop with select on main eventChannel and quit channel
- ReactorEngine main loop control with Start() Stop() Flush()
- ReactorEngine.dispatch
- use sync.RWMutex
- delete eventHandler if subscribed channels go to 0

ethreact/reactor.go

@@ -0,0 +1,175 @@
+package ethreact
+
+import (
+	"github.com/ethereum/eth-go/ethlog"
+	"sync"
+)
+
+var logger = ethlog.NewLogger("REACTOR")
+
+type EventHandler struct {
+	lock  sync.RWMutex
+	name  string
+	chans []chan Event
+}
+
+// Post the Event with the reactor resource on the channels
+// currently subscribed to the event
+func (e *EventHandler) Post(event Event) {
+	e.lock.RLock()
+	defer e.lock.RUnlock()
+
+	// if we want to preserve order pushing to subscibed channels
+	// dispatching should be syncrounous
+	// this means if subscribed event channel is blocked (closed or has fixed capacity)
+	// the reactor dispatch will be blocked, so we need to mitigate by skipping
+	// rogue blocking subscribers
+	for i, ch := range e.chans {
+		select {
+		case ch <- event:
+		default:
+			logger.Warnln("subscribing channel %d to event %s blocked. skipping", i, event.Name)
+		}
+	}
+}
+
+// Add a subscriber to this event
+func (e *EventHandler) Add(ch chan Event) {
+	e.lock.Lock()
+	defer e.lock.Unlock()
+
+	e.chans = append(e.chans, ch)
+}
+
+// Remove a subscriber
+func (e *EventHandler) Remove(ch chan Event) int {
+	e.lock.Lock()
+	defer e.lock.Unlock()
+
+	for i, c := range e.chans {
+		if c == ch {
+			e.chans = append(e.chans[:i], e.chans[i+1:]...)
+		}
+	}
+	return len(e.chans)
+}
+
+// Basic reactor resource
+type Event struct {
+	Resource interface{}
+	Name     string
+}
+
+// The reactor basic engine. Acts as bridge
+// between the events and the subscribers/posters
+type ReactorEngine struct {
+	lock            sync.RWMutex
+	eventChannel    chan Event
+	eventHandlers   map[string]*EventHandler
+	quit            chan bool
+	shutdownChannel chan bool
+	running         bool
+	drained         bool
+}
+
+func New() *ReactorEngine {
+	return &ReactorEngine{
+		eventHandlers:   make(map[string]*EventHandler),
+		eventChannel:    make(chan Event),
+		quit:            make(chan bool, 1),
+		shutdownChannel: make(chan bool, 1),
+	}
+}
+
+func (reactor *ReactorEngine) Start() {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+	if !reactor.running {
+		go func() {
+		out:
+			for {
+				select {
+				case <-reactor.quit:
+					break out
+				case event := <-reactor.eventChannel:
+					// needs to be called syncronously to keep order of events
+					reactor.dispatch(event)
+				default:
+					reactor.drained = true
+				}
+			}
+			reactor.lock.Lock()
+			defer reactor.lock.Unlock()
+			reactor.running = false
+			logger.Infoln("stopped")
+			close(reactor.shutdownChannel)
+		}()
+		reactor.running = true
+		logger.Infoln("started")
+	}
+}
+
+func (reactor *ReactorEngine) Stop() {
+	reactor.lock.RLock()
+	if reactor.running {
+		reactor.quit <- true
+	}
+	reactor.lock.RUnlock()
+	<-reactor.shutdownChannel
+}
+
+func (reactor *ReactorEngine) Flush() {
+	for !reactor.drained {
+	}
+}
+
+// Subscribe a channel to the specified event
+func (reactor *ReactorEngine) Subscribe(event string, eventChannel chan Event) {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+
+	eventHandler := reactor.eventHandlers[event]
+	// Create a new event handler if one isn't available
+	if eventHandler == nil {
+		eventHandler = &EventHandler{name: event}
+		reactor.eventHandlers[event] = eventHandler
+	}
+	// Add the events channel to reactor event handler
+	eventHandler.Add(eventChannel)
+	logger.Debugln("added new subscription to %s", event)
+}
+
+func (reactor *ReactorEngine) Unsubscribe(event string, eventChannel chan Event) {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+
+	eventHandler := reactor.eventHandlers[event]
+	if eventHandler != nil {
+		len := eventHandler.Remove(eventChannel)
+		if len == 0 {
+			reactor.eventHandlers[event] = nil
+		}
+		logger.Debugln("removed subscription to %s", event)
+	}
+}
+
+func (reactor *ReactorEngine) Post(event string, resource interface{}) {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+
+	if reactor.running {
+		reactor.drained = false
+		reactor.eventChannel <- Event{Resource: resource, Name: event}
+	}
+}
+
+func (reactor *ReactorEngine) dispatch(event Event) {
+	name := event.Name
+	eventHandler := reactor.eventHandlers[name]
+	// if no subscriptions to this event type - no event handler created
+	// then noone to notify
+	if eventHandler != nil {
+		// needs to be called syncronously
+		eventHandler.Post(event)
+	}
+}