ListenerConn: Improve implementation of Close

The previous coding was both unsafe (since it tried to operate on the
connection without holding senderLock), but also in some cases failed to
wake up ongoing queries.

notify.go

@@ -283,13 +283,13 @@ func (l *ListenerConn) ExecSimpleQuery(q string) (executed bool, err error) {
 		// We can't know what state the protocol is in, so we need to abandon
 		// this connection.
 		l.connectionLock.Lock()
-		defer l.connectionLock.Unlock()
 		// Set the error pointer if it hasn't been set already; see
 		// listenerConnMain.
 		if l.err == nil {
 			l.err = err
 		}
-		l.cn.Close()
+		l.connectionLock.Unlock()
+		l.cn.c.Close()
 		return false, err
 	}
 
@@ -329,12 +329,15 @@ func (l *ListenerConn) ExecSimpleQuery(q string) (executed bool, err error) {
 
 func (l *ListenerConn) Close() error {
 	l.connectionLock.Lock()
-	defer l.connectionLock.Unlock()
 	if l.err != nil {
+		l.connectionLock.Unlock()
 		return errListenerConnClosed
 	}
 	l.err = errListenerConnClosed
-	return l.cn.Close()
+	l.connectionLock.Unlock()
+	// We can't send anything on the connection without holding senderLock.
+	// Simply close the net.Conn to wake up everyone operating on it.
+	return l.cn.c.Close()
 }
 
 // Err() returns the reason the connection was closed.  It is not safe to call

notify_test.go

@@ -232,8 +232,8 @@ func TestConnExecDeadlock(t *testing.T) {
 	}()
 	// give the two goroutines some time to get into position
 	runtime.Gosched()
-	// simulate network connection failure
-	l.cn.c.Close()
+	// calls Close on the net.Conn; equivalent to a network failure
+	l.Close()
 
 	var done int32 = 0
 	go func() {
@@ -246,6 +246,42 @@ func TestConnExecDeadlock(t *testing.T) {
 	atomic.StoreInt32(&done, 1)
 }
 
+// Test for ListenerConn being closed while a slow query is executing
+func TestListenerConnCloseWhileQueryIsExecuting(t *testing.T) {
+	l, _ := newTestListenerConn(t)
+	defer l.Close()
+
+	var wg sync.WaitGroup
+	wg.Add(1)
+
+	go func() {
+		sent, err := l.ExecSimpleQuery("SELECT pg_sleep(60)")
+		if sent {
+			panic("expected sent=false")
+		}
+		// could be any of a number of errors
+		if err == nil {
+			panic("expected error")
+		}
+		wg.Done()
+	}()
+	// give the above goroutine some time to get into position
+	runtime.Gosched()
+	err := l.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+	var done int32 = 0
+	go func() {
+		time.Sleep(10 * time.Second)
+		if atomic.LoadInt32(&done) != 1 {
+			panic("timed out")
+		}
+	}()
+	wg.Wait()
+	atomic.StoreInt32(&done, 1)
+}
+
 func TestNotifyExtra(t *testing.T) {
 	db := openTestConn(t)
 	defer db.Close()