Only close epoller FD at most once.

console_linux.go

@@ -58,6 +58,7 @@ type Epoller struct {
 	efd       int
 	mu        sync.Mutex
 	fdMapping map[int]*EpollConsole
+	closeOnce sync.Once
 }
 
 // NewEpoller returns an instance of epoller with a valid epoll fd.
@@ -151,7 +152,11 @@ func (e *Epoller) getConsole(sysfd int) *EpollConsole {
 
 // Close closes the epoll fd
 func (e *Epoller) Close() error {
-	return unix.Close(e.efd)
+	closeErr := os.ErrClosed // default to "file already closed"
+	e.closeOnce.Do(func() {
+		closeErr = unix.Close(e.efd)
+	})
+	return closeErr
 }
 
 // EpollConsole acts like a console but registers its file descriptor with an

console_linux_test.go

@@ -85,4 +85,12 @@ func TestEpollConsole(t *testing.T) {
 	if out := b.String(); out != expectedOutput {
 		t.Errorf("unexpected output %q", out)
 	}
+
+	// make sure multiple Close calls return os.ErrClosed after the first
+	if err := epoller.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := epoller.Close(); err != os.ErrClosed {
+		t.Fatalf("unexpected error returned from second call to epoller.Close(): %v", err)
+	}
 }