Fixed start/stop handling of Discovery (#1346)

Author: cmaglie

arduino/discovery/discovery.go

@@ -95,7 +95,6 @@ func New(id string, args ...string) (*PluggableDiscovery, error) {
 		process:              proc,
 		incomingMessagesChan: messageChan,
 		outgoingCommandsPipe: stdin,
-		alive:                true,
 	}
 	go disc.jsonDecodeLoop(stdout, messageChan)
 	return disc, nil
@@ -118,6 +117,7 @@ func (disc *PluggableDiscovery) jsonDecodeLoop(in io.Reader, outChan chan<- *dis
 		disc.incomingMessagesError = err
 		disc.statusMutex.Unlock()
 		close(outChan)
+		// TODO: Try restarting process some times before closing it completely
 	}
 
 	for {
@@ -202,6 +202,9 @@ func (disc *PluggableDiscovery) runProcess() error {
 	if err := disc.process.Start(); err != nil {
 		return err
 	}
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	disc.alive = true
 	return nil
 }
 
@@ -257,6 +260,13 @@ func (disc *PluggableDiscovery) Stop() error {
 	} else if msg.Message != "OK" || msg.Error {
 		return errors.Errorf("command failed: %s", msg.Message)
 	}
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	if disc.eventChan != nil {
+		close(disc.eventChan)
+		disc.eventChan = nil
+	}
+	disc.eventsMode = false
 	return nil
 }
 
@@ -272,6 +282,13 @@ func (disc *PluggableDiscovery) Quit() error {
 	} else if msg.Message != "OK" || msg.Error {
 		return errors.Errorf("command failed: %s", msg.Message)
 	}
+	disc.statusMutex.Lock()
+	defer disc.statusMutex.Unlock()
+	if disc.eventChan != nil {
+		close(disc.eventChan)
+		disc.eventChan = nil
+	}
+	disc.alive = false
 	return nil
 }
 
@@ -296,9 +313,14 @@ func (disc *PluggableDiscovery) List() ([]*Port, error) {
 // The event channel must be consumed as quickly as possible since it may block the
 // discovery if it becomes full. The channel size is configurable.
 func (disc *PluggableDiscovery) EventChannel(size int) <-chan *Event {
-	c := make(chan *Event, size)
 	disc.statusMutex.Lock()
 	defer disc.statusMutex.Unlock()
+	if disc.eventChan != nil {
+		// In case there is already an existing event channel in use we close it
+		// before creating a new one.
+		close(disc.eventChan)
+	}
+	c := make(chan *Event, size)
 	disc.eventChan = c
 	return c
 }