2 files changed, 245 insertions, 0 deletions
diff --git a/ethreact/reactor.go b/ethreact/reactor.go
new file mode 100644
index 000000000..a26f82a97
--- /dev/null
+++ b/ethreact/reactor.go
@@ -0,0 +1,182 @@
+package ethreact
+
+import (
+	"github.com/ethereum/eth-go/ethlog"
+	"sync"
+)
+
+var logger = ethlog.NewLogger("REACTOR")
+
+const (
+	eventBufferSize int = 10
+)
+
+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
+	// 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.Warnf("subscribing channel %d to event %s blocked. skipping\n", 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 chan error
+	running       bool
+	drained       chan bool
+}
+
+func New() *ReactorEngine {
+	return &ReactorEngine{
+		eventHandlers: make(map[string]*EventHandler),
+		eventChannel:  make(chan Event, eventBufferSize),
+		quit:          make(chan chan error, 1),
+		drained:       make(chan bool, 1),
+	}
+}
+
+func (reactor *ReactorEngine) Start() {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+	if !reactor.running {
+		go func() {
+			for {
+				select {
+				case status := <-reactor.quit:
+					reactor.lock.Lock()
+					defer reactor.lock.Unlock()
+					reactor.running = false
+					logger.Infoln("stopped")
+					status <- nil
+					return
+				case event := <-reactor.eventChannel:
+					// needs to be called syncronously to keep order of events
+					reactor.dispatch(event)
+				default:
+					reactor.drained <- true // blocking till message is coming in
+				}
+			}
+		}()
+		reactor.running = true
+		logger.Infoln("started")
+	}
+}
+
+func (reactor *ReactorEngine) Stop() {
+	if reactor.running {
+		status := make(chan error)
+		reactor.quit <- status
+		select {
+		case <-reactor.drained:
+		default:
+		}
+		<-status
+	}
+}
+
+func (reactor *ReactorEngine) Flush() {
+	<-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.Debugf("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.Debugf("removed subscription to %s", event)
+	}
+}
+
+func (reactor *ReactorEngine) Post(event string, resource interface{}) {
+	reactor.lock.Lock()
+	defer reactor.lock.Unlock()
+
+	if reactor.running {
+		reactor.eventChannel <- Event{Resource: resource, Name: event}
+		select {
+		case <-reactor.drained:
+		default:
+		}
+	}
+}
+
+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)
+	}
+}
diff --git a/ethreact/reactor_test.go b/ethreact/reactor_test.go
new file mode 100644
index 000000000..801a8abd0
--- /dev/null
+++ b/ethreact/reactor_test.go
@@ -0,0 +1,63 @@
+package ethreact
+
+import (
+	"fmt"
+	"testing"
+)
+
+func TestReactorAdd(t *testing.T) {
+	reactor := New()
+	ch := make(chan Event)
+	reactor.Subscribe("test", ch)
+	if reactor.eventHandlers["test"] == nil {
+		t.Error("Expected new eventHandler to be created")
+	}
+	reactor.Unsubscribe("test", ch)
+	if reactor.eventHandlers["test"] != nil {
+		t.Error("Expected eventHandler to be removed")
+	}
+}
+
+func TestReactorEvent(t *testing.T) {
+	var name string
+	reactor := New()
+	// Buffer the channel, so it doesn't block for this test
+	cap := 20
+	ch := make(chan Event, cap)
+	reactor.Subscribe("even", ch)
+	reactor.Subscribe("odd", ch)
+	reactor.Post("even", "disappears") // should not broadcast if engine not started
+	reactor.Start()
+	for i := 0; i < cap; i++ {
+		if i%2 == 0 {
+			name = "even"
+		} else {
+			name = "odd"
+		}
+		reactor.Post(name, i)
+	}
+	reactor.Post("test", cap) // this should not block
+	i := 0
+	reactor.Flush()
+	close(ch)
+	for event := range ch {
+		fmt.Printf("%d: %v", i, event)
+		if i%2 == 0 {
+			name = "even"
+		} else {
+			name = "odd"
+		}
+		if val, ok := event.Resource.(int); ok {
+			if i != val || event.Name != name {
+				t.Error("Expected event %d to be of type %s and resource %d, got ", i, name, i, val)
+			}
+		} else {
+			t.Error("Unable to cast")
+		}
+		i++
+	}
+	if i != cap {
+		t.Error("excpected exactly %d events, got ", i)
+	}
+	reactor.Stop()
+}