Split handlers up into three groups.

client/connection.go

@@ -22,7 +22,9 @@ type Conn struct {
 	cfg *Config
 
 	// Handlers
-	handlers *hSet
+	intHandlers *hSet
+	fgHandlers *hSet
+	bgHandlers *hSet
 
 	// State tracker for nicks and channels
 	st         state.Tracker
@@ -119,7 +121,9 @@ func Client(cfg *Config) *Conn {
 		cfg:         cfg,
 		in:          make(chan *Line, 32),
 		out:         make(chan string, 32),
-		handlers:   handlerSet(),
+		intHandlers: handlerSet(),
+		fgHandlers:  handlerSet(),
+		bgHandlers:  handlerSet(),
 		stRemovers:  make([]Remover, 0, len(stHandlers)),
 		lastsent:    time.Now(),
 	}

client/connection_test.go

@@ -87,7 +87,7 @@ func TestClientAndStateTracking(t *testing.T) {
 	}
 	// Check that the internal handlers are correctly set up
 	for k, _ := range intHandlers {
-		if _, ok := c.handlers.set[strings.ToLower(k)]; !ok {
+		if _, ok := c.intHandlers.set[strings.ToLower(k)]; !ok {
 			t.Errorf("Missing internal handler for '%s'.", k)
 		}
 	}
@@ -95,7 +95,7 @@ func TestClientAndStateTracking(t *testing.T) {
 	// Now enable the state tracking code and check its handlers
 	c.EnableStateTracking()
 	for k, _ := range stHandlers {
-		if _, ok := c.handlers.set[strings.ToLower(k)]; !ok {
+		if _, ok := c.intHandlers.set[strings.ToLower(k)]; !ok {
 			t.Errorf("Missing state handler for '%s'.", k)
 		}
 	}
@@ -124,7 +124,7 @@ func TestClientAndStateTracking(t *testing.T) {
 
 	// Finally, check state tracking handlers were all removed correctly
 	for k, _ := range stHandlers {
-		if _, ok := c.handlers.set[strings.ToLower(k)]; ok && k != "NICK" {
+		if _, ok := c.intHandlers.set[strings.ToLower(k)]; ok && k != "NICK" {
 			// A bit leaky, because intHandlers adds a NICK handler.
 			t.Errorf("State handler for '%s' not removed correctly.", k)
 		}

client/dispatch.go

@@ -121,9 +121,15 @@ func (hs *hSet) dispatch(conn *Conn, line *Line) {
 	if !ok {
 		return
 	}
+	wg := &sync.WaitGroup{}
 	for hn := list.start; hn != nil; hn = hn.next {
-		go hn.Handle(conn, line.Copy())
+		wg.Add(1)
+		go func(hn *hNode) {
+			hn.Handle(conn, line.Copy())
+			wg.Done()
+		}(hn)
 	}
+	wg.Wait()
 }
 
 // Handlers are triggered on incoming Lines from the server, with the handler
@@ -133,7 +139,15 @@ func (hs *hSet) dispatch(conn *Conn, line *Line) {
 // strings of digits like "332" (mainly because I really didn't feel like
 // putting massive constant tables in).
 func (conn *Conn) Handle(name string, h Handler) Remover {
-	return conn.handlers.add(name, h)
+	return conn.fgHandlers.add(name, h)
+}
+
+func (conn *Conn) HandleBG(name string, h Handler) Remover {
+	return conn.bgHandlers.add(name, h)
+}
+
+func (conn *Conn) handle(name string, h Handler) Remover {
+	return conn.intHandlers.add(name, h)
 }
 
 func (conn *Conn) HandleFunc(name string, hf HandlerFunc) Remover {
@@ -141,7 +155,18 @@ func (conn *Conn) HandleFunc(name string, hf HandlerFunc) Remover {
 }
 
 func (conn *Conn) dispatch(line *Line) {
-	conn.handlers.dispatch(conn, line)
+	// We run the internal handlers first, including all state tracking ones.
+	// This ensures that user-supplied handlers that use the tracker have a
+	// consistent view of the connection state in handlers that mutate it.
+	conn.intHandlers.dispatch(conn, line)
+	// Background handlers are run in parallel and do not block the event loop.
+	// This is useful for things that may need to do significant work.
+	go conn.bgHandlers.dispatch(conn, line)
+	// Foreground handlers have a guarantee of protocol consistency: all the
+	// handlers for one event will have finished before the handlers for the
+	// next start processing. They are run in parallel but block the event
+	// loop, so care should be taken to ensure these handlers are quick :-)
+	conn.fgHandlers.dispatch(conn, line)
 }
 
 func (conn *Conn) LogPanic(line *Line) {

client/handlers.go

@@ -21,7 +21,7 @@ func (conn *Conn) addIntHandlers() {
 	for n, h := range intHandlers {
 		// internal handlers are essential for the IRC client
 		// to function, so we don't save their Removers here
-		conn.Handle(n, h)
+		conn.handle(n, h)
 	}
 }
 

client/state_handlers.go

@@ -26,7 +26,7 @@ var stHandlers = map[string]HandlerFunc{
 
 func (conn *Conn) addSTHandlers() {
 	for n, h := range stHandlers {
-		conn.stRemovers = append(conn.stRemovers, conn.Handle(n, h))
+		conn.stRemovers = append(conn.stRemovers, conn.handle(n, h))
 	}
 }