Wait until the older clipmenud holds the lock before the launcher starts (issue 1814, S1)

modules/clipmenu/cmd/clipmenu-tools/manifest_test.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bufio"
 	"context"
 	"net"
 	"os"
@@ -170,20 +171,33 @@ func TestTheLauncherWaitsQuietlyWhileAnotherClipmenudHoldsTheLock(t *testing.T)
 	store := dir + "/cm/clipmenu.6.op"
 	os.MkdirAll(store, 0o700)
 	lock := store + "/session_lock"
-	// the older clipmenud: it holds the lock the way clipmenud does, until it is killed
-	holder := exec.Command("flock", "-x", "-n", lock, "sleep", "60")
+	// the older clipmenud: it holds the lock the way clipmenud does, until it is killed. It says "held" once it has the
+	// lock, so the test goes on only when the lock is held for certain: a holder that is slow to start (the checker
+	// runs thousands of tests at once) must not let the launcher find the lock free (issue 1814).
+	holder := exec.Command("flock", "-x", "-n", lock, "sh", "-c", "echo held; exec sleep 60")
 	holder.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	held, err := holder.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
 	if err := holder.Start(); err != nil {
 		t.Fatal(err)
 	}
 	// flock's child shares the lock, so the whole group goes
 	release := func() { syscall.Kill(-holder.Process.Pid, syscall.SIGKILL); holder.Wait() }
 	defer release()
-	for i := 0; i < 50; i++ {
-		if probe := exec.Command("flock", "-n", lock, "true"); probe.Run() != nil {
-			break
+	said := make(chan string, 1)
+	go func() {
+		line, _ := bufio.NewReader(held).ReadString('\n')
+		said <- strings.TrimSpace(line)
+	}()
+	select {
+	case line := <-said:
+		if line != "held" {
+			t.Fatalf("the older clipmenud did not take the lock: %q", line)
 		}
-		time.Sleep(50 * time.Millisecond)
+	case <-time.After(30 * time.Second):
+		t.Fatal("the older clipmenud did not take the lock within 30 s")
 	}
 	var out syncBuffer
 	cmd := exec.Command("sh", file)