test(runtime): keep the Xvfb displayfd read end open until cleanup

Closing it right after the first read made Xvfb's later displayfd write fail on a server reset ('Cannot write display number to fd 3'), killing the server under load. Reproduced on ubuntu:26.04 Xvfb 21.1.22 with CPU contention: 8/200 failures before, 0/200 after.

commit: 5f9aee7852c50d4df9eaddf46f0ffa36d8527d47
author: brice · 27h ago · 2026-10-22 09:35 UTC
parent: f2df270
signature: GPG VerifiedCD88F9E564E0102646FB6077A1A07C7C7C3E349D · arch-gpg Verified for the committer email
checks: 4/4

2 files · +6 -2

M conn_xserver_test.go +3 -1


@@ -31,7 +31,9 @@ func startXvfb(t *testing.T, authFile string) string {
31	31		if err != nil {
32	32		t.Fatal(err)
33	33		}
34		-	defer r.Close()
	34	+	// Xvfb may write to -displayfd again (e.g. after a server reset); closing
	35	+	// the read end early makes that write fail and kills the server.
	36	+	t.Cleanup(func() { _ = r.Close() })
35	37		cmd := exec.Command("Xvfb", "-displayfd", "3", "-screen", "0", "800x600x24", "-nolisten", "tcp", "-auth", authFile)
36	38		cmd.ExtraFiles = []*os.File{w}
37	39		var log bytes.Buffer

 	if err != nil {
 		t.Fatal(err)
 	}
-	defer r.Close()
+	// Xvfb may write to -displayfd again (e.g. after a server reset); closing
+	// the read end early makes that write fail and kills the server.
+	t.Cleanup(func() { _ = r.Close() })
 	cmd := exec.Command("Xvfb", "-displayfd", "3", "-screen", "0", "800x600x24", "-nolisten", "tcp", "-auth", authFile)
 	cmd.ExtraFiles = []*os.File{w}
 	var log bytes.Buffer

M internal/xtest/capture_test.go +3 -1


@@ -101,7 +101,9 @@ func TestCaptureRequests(t *testing.T) {
101	101		if err != nil {
102	102		t.Fatal(err)
103	103		}
104		-	defer r.Close()
	104	+	// Xvfb writes to displayfd again after a server reset; keep the read end
	105	+	// open until the test ends so that write cannot kill the server.
	106	+	t.Cleanup(func() { _ = r.Close() })
105	107		cmd := exec.Command("Xvfb", xvfbArgs()...)
106	108		cmd.ExtraFiles = []*os.File{w}
107	109		var log bytes.Buffer

 	if err != nil {
 		t.Fatal(err)
 	}
-	defer r.Close()
+	// Xvfb writes to displayfd again after a server reset; keep the read end
+	// open until the test ends so that write cannot kill the server.
+	t.Cleanup(func() { _ = r.Close() })
 	cmd := exec.Command("Xvfb", xvfbArgs()...)
 	cmd.ExtraFiles = []*os.File{w}
 	var log bytes.Buffer