server: Use channel to communicate shutdown

server.go

@@ -7,7 +7,6 @@ import (
 	"log"
 	"net"
 	"sync"
-	"sync/atomic"
 	"time"
 )
 
@@ -46,11 +45,11 @@ type Server struct {
 	// If nil, logging is done via the log package's standard logger.
 	ErrorLog *log.Logger
 
-	listeners map[*net.Listener]context.CancelFunc
-	conns     map[*net.Conn]context.CancelFunc
-	doneChan  chan struct{}
-	status    int32
-	mu        sync.Mutex
+	listeners  map[*net.Listener]struct{}
+	conns      map[*net.Conn]struct{}
+	closedChan chan struct{} // closed when the server is closed
+	doneChan   chan struct{} // closed when no more connections are open
+	mu         sync.Mutex
 }
 
 const (
@@ -59,7 +58,22 @@ const (
 	serverClosed
 )
 
-// done returns a channel that's closed when the server has finished closing.
+// closed returns a channel that's closed when the server is closed.
+func (srv *Server) closed() chan struct{} {
+	srv.mu.Lock()
+	defer srv.mu.Unlock()
+	return srv.closedLocked()
+}
+
+func (srv *Server) closedLocked() chan struct{} {
+	if srv.closedChan == nil {
+		srv.closedChan = make(chan struct{})
+	}
+	return srv.closedChan
+}
+
+// done returns a channel that's closed when the server is closed and
+// all listeners and connections are closed.
 func (srv *Server) done() chan struct{} {
 	srv.mu.Lock()
 	defer srv.mu.Unlock()
@@ -73,28 +87,22 @@ func (srv *Server) doneLocked() chan struct{} {
 	return srv.doneChan
 }
 
-// rejectingListeners reports whether the server is rejecting new listeners
-// (e.g. after Shutdown or Close has been called).
-func (srv *Server) rejectingListeners() bool {
-	return atomic.LoadInt32(&srv.status) != serverOk
-}
-
-// rejectingConns reports whether the server is rejecting new connections
-// (e.g. after Close has been called).
-func (srv *Server) rejectingConns() bool {
-	return atomic.LoadInt32(&srv.status) == serverClosed
-}
-
-// tryFinishShutdown closes srv.done() if there are no active listeners or requests.
+// tryFinishShutdown closes srv.done() if the server is closed and
+// there are no active listeners or connections.
 func (srv *Server) tryFinishShutdown() {
 	srv.mu.Lock()
 	defer srv.mu.Unlock()
+	select {
+	case <-srv.closedLocked():
+	default:
+		return
+	}
 	if len(srv.listeners) == 0 && len(srv.conns) == 0 {
-		done := srv.doneLocked()
+		ch := srv.doneLocked()
 		select {
-		case <-done:
+		case <-ch:
 		default:
-			close(done)
+			close(ch)
 		}
 	}
 }
@@ -102,17 +110,20 @@ func (srv *Server) tryFinishShutdown() {
 // Close immediately closes all active net.Listeners and connections.
 // For a graceful shutdown, use Shutdown.
 func (srv *Server) Close() error {
-	if !atomic.CompareAndSwapInt32(&srv.status, serverOk, serverClosed) {
-		return ErrServerClosed
+	ch := srv.closed()
+	select {
+	case <-ch:
+		return nil
+	default:
+		close(ch)
 	}
 
-	// Close active listeners and connections.
+	srv.tryFinishShutdown()
+
+	// Force all active connections to close.
 	srv.mu.Lock()
-	for _, cancel := range srv.listeners {
-		cancel()
-	}
-	for _, cancel := range srv.conns {
-		cancel()
+	for conn := range srv.conns {
+		(*conn).Close()
 	}
 	srv.mu.Unlock()
 
@@ -129,24 +140,22 @@ func (srv *Server) Close() error {
 // If the provided context expires before the shutdown is complete,
 // Shutdown returns the context's error.
 //
-// When Shutdown is called, Serve and ListenAndServer immediately
+// When Shutdown is called, Serve and ListenAndServe immediately
 // return ErrServerClosed. Make sure the program doesn't exit and
 // waits instead for Shutdown to return.
 //
 // Once Shutdown has been called on a server, it may not be reused;
 // future calls to methods such as Serve will return ErrServerClosed.
 func (srv *Server) Shutdown(ctx context.Context) error {
-	if !atomic.CompareAndSwapInt32(&srv.status, serverOk, serverShutdown) {
-		return ErrServerClosed
+	ch := srv.closed()
+	select {
+	case <-ch:
+		return nil
+	default:
+		close(ch)
 	}
-	defer atomic.StoreInt32(&srv.status, serverClosed)
 
-	// Close active listeners.
-	srv.mu.Lock()
-	for _, cancel := range srv.listeners {
-		cancel()
-	}
-	srv.mu.Unlock()
+	srv.tryFinishShutdown()
 
 	// Wait for active connections to finish.
 	select {
@@ -166,8 +175,10 @@ func (srv *Server) Shutdown(ctx context.Context) error {
 // ListenAndServe always returns a non-nil error. After Shutdown or Close, the
 // returned error is ErrServerClosed.
 func (srv *Server) ListenAndServe(ctx context.Context) error {
-	if srv.rejectingListeners() {
+	select {
+	case <-srv.closed():
 		return ErrServerClosed
+	default:
 	}
 
 	addr := srv.Addr
@@ -195,16 +206,18 @@ func (srv *Server) getCertificate(h *tls.ClientHelloInfo) (*tls.Certificate, err
 	return srv.GetCertificate(h.ServerName)
 }
 
-func (srv *Server) trackListener(l *net.Listener, cancel context.CancelFunc) bool {
-	if srv.rejectingListeners() {
-		return false
-	}
+func (srv *Server) trackListener(l *net.Listener) bool {
 	srv.mu.Lock()
 	defer srv.mu.Unlock()
-	if srv.listeners == nil {
-		srv.listeners = make(map[*net.Listener]context.CancelFunc)
+	select {
+	case <-srv.closedLocked():
+		return false
+	default:
 	}
-	srv.listeners[l] = cancel
+	if srv.listeners == nil {
+		srv.listeners = make(map[*net.Listener]struct{})
+	}
+	srv.listeners[l] = struct{}{}
 	return true
 }
 
@@ -223,10 +236,7 @@ func (srv *Server) deleteListener(l *net.Listener) {
 func (srv *Server) Serve(ctx context.Context, l net.Listener) error {
 	defer l.Close()
 
-	lnctx, cancel := context.WithCancel(ctx)
-	defer cancel()
-
-	if !srv.trackListener(&l, cancel) {
+	if !srv.trackListener(&l) {
 		return ErrServerClosed
 	}
 	defer srv.tryFinishShutdown()
@@ -238,13 +248,12 @@ func (srv *Server) Serve(ctx context.Context, l net.Listener) error {
 	}()
 
 	select {
-	case <-lnctx.Done():
-		if srv.rejectingListeners() {
-			return ErrServerClosed
-		}
-		return lnctx.Err()
+	case <-ctx.Done():
+		return ctx.Err()
 	case err := <-errch:
 		return err
+	case <-srv.closed():
+		return ErrServerClosed
 	}
 }
 
@@ -274,17 +283,13 @@ func (srv *Server) serve(ctx context.Context, l net.Listener) error {
 	}
 }
 
-func (srv *Server) trackConn(conn *net.Conn, cancel context.CancelFunc) bool {
-	if srv.rejectingConns() {
-		return false
-	}
+func (srv *Server) trackConn(conn *net.Conn) {
 	srv.mu.Lock()
 	defer srv.mu.Unlock()
 	if srv.conns == nil {
-		srv.conns = make(map[*net.Conn]context.CancelFunc)
+		srv.conns = make(map[*net.Conn]struct{})
 	}
-	srv.conns[conn] = cancel
-	return true
+	srv.conns[conn] = struct{}{}
 }
 
 func (srv *Server) deleteConn(conn *net.Conn) {
@@ -295,16 +300,11 @@ func (srv *Server) deleteConn(conn *net.Conn) {
 
 // ServeConn serves a Gemini response over the provided connection.
 // It closes the connection when the response has been completed.
-// Note that ServeConn will succeed even if a Shutdown is in progress.
+// ServeConn can be used even after Shutdown or Close have been called.
 func (srv *Server) ServeConn(ctx context.Context, conn net.Conn) error {
 	defer conn.Close()
 
-	ctx, cancel := context.WithCancel(ctx)
-	defer cancel()
-
-	if !srv.trackConn(&conn, cancel) {
-		return ErrServerClosed
-	}
+	srv.trackConn(&conn)
 	defer srv.tryFinishShutdown()
 	defer srv.deleteConn(&conn)
 
@@ -322,9 +322,6 @@ func (srv *Server) ServeConn(ctx context.Context, conn net.Conn) error {
 
 	select {
 	case <-ctx.Done():
-		if srv.rejectingConns() {
-			return ErrServerClosed
-		}
 		return ctx.Err()
 	case err := <-errch:
 		return err