os/signal: derive TestAtomicStop timeout from overall test timeout

Previously, TestAtomicStop used a hard-coded 2-second timeout.

That empirically is not long enough on certain builders. Rather than
adjusting it to a different arbitrary value, use a slice of the
overall timeout for the test binary. If everything is working, we
won't block nearly that long anyway.

Updates #35085

Change-Id: I7b789388e3152413395088088fc497419976cf5c
Reviewed-on: https://go-review.googlesource.com/c/go/+/203499
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/os/signal/signal_test.go

@@ -22,6 +22,22 @@ import (
 	"time"
 )
 
+var testDeadline time.Time
+
+func TestMain(m *testing.M) {
+	flag.Parse()
+
+	// TODO(golang.org/issue/28135): Remove this setup and use t.Deadline instead.
+	timeoutFlag := flag.Lookup("test.timeout")
+	if timeoutFlag != nil {
+		if d := timeoutFlag.Value.(flag.Getter).Get().(time.Duration); d != 0 {
+			testDeadline = time.Now().Add(d)
+		}
+	}
+
+	os.Exit(m.Run())
+}
+
 func waitSig(t *testing.T, c <-chan os.Signal, sig os.Signal) {
 	// Sleep multiple times to give the kernel more tries to
 	// deliver the signal.
@@ -392,7 +408,11 @@ func TestAtomicStop(t *testing.T) {
 
 	const execs = 10
 	for i := 0; i < execs; i++ {
-		cmd := exec.Command(os.Args[0], "-test.run=TestAtomicStop")
+		timeout := "0"
+		if !testDeadline.IsZero() {
+			timeout = testDeadline.Sub(time.Now()).String()
+		}
+		cmd := exec.Command(os.Args[0], "-test.run=TestAtomicStop", "-test.timeout="+timeout)
 		cmd.Env = append(os.Environ(), "GO_TEST_ATOMIC_STOP=1")
 		out, err := cmd.CombinedOutput()
 		if err == nil {
@@ -431,6 +451,14 @@ func TestAtomicStop(t *testing.T) {
 // either catch a signal or die from it.
 func atomicStopTestProgram() {
 	const tries = 10
+
+	timeout := 2 * time.Second
+	if !testDeadline.IsZero() {
+		// Give each try an equal slice of the deadline, with one slice to spare for
+		// cleanup.
+		timeout = testDeadline.Sub(time.Now()) / (tries + 1)
+	}
+
 	pid := syscall.Getpid()
 	printed := false
 	for i := 0; i < tries; i++ {
@@ -453,7 +481,7 @@ func atomicStopTestProgram() {
 
 		select {
 		case <-cs:
-		case <-time.After(2 * time.Second):
+		case <-time.After(timeout):
 			if !printed {
 				fmt.Print("lost signal on tries:")
 				printed = true