os/signal: add NotifyContext to cancel context using system signals

Fixes #37255

Change-Id: Ic0fde3498afefed6e4447f8476e4da7c1faa7145
Reviewed-on: https://go-review.googlesource.com/c/go/+/219640
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Trust: Giovanni Bajo <rasky@develer.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/os/signal/signal_test.go

@@ -8,6 +8,7 @@ package signal
 
 import (
 	"bytes"
+	"context"
 	"flag"
 	"fmt"
 	"internal/testenv"
@@ -674,3 +675,164 @@ func TestTime(t *testing.T) {
 	close(stop)
 	<-done
 }
+
+func TestNotifyContext(t *testing.T) {
+	c, stop := NotifyContext(context.Background(), syscall.SIGINT)
+	defer stop()
+
+	if want, got := "signal.NotifyContext(context.Background, [interrupt])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+
+	syscall.Kill(syscall.Getpid(), syscall.SIGINT)
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("timed out waiting for context to be done after SIGINT")
+	}
+}
+
+func TestNotifyContextStop(t *testing.T) {
+	Ignore(syscall.SIGHUP)
+	if !Ignored(syscall.SIGHUP) {
+		t.Errorf("expected SIGHUP to be ignored when explicitly ignoring it.")
+	}
+
+	parent, cancelParent := context.WithCancel(context.Background())
+	defer cancelParent()
+	c, stop := NotifyContext(parent, syscall.SIGHUP)
+	defer stop()
+
+	// If we're being notified, then the signal should not be ignored.
+	if Ignored(syscall.SIGHUP) {
+		t.Errorf("expected SIGHUP to not be ignored.")
+	}
+
+	if want, got := "signal.NotifyContext(context.Background.WithCancel, [hangup])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, wanted %q", got, want)
+	}
+
+	stop()
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("timed out waiting for context to be done after calling stop")
+	}
+}
+
+func TestNotifyContextCancelParent(t *testing.T) {
+	parent, cancelParent := context.WithCancel(context.Background())
+	defer cancelParent()
+	c, stop := NotifyContext(parent, syscall.SIGINT)
+	defer stop()
+
+	if want, got := "signal.NotifyContext(context.Background.WithCancel, [interrupt])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+
+	cancelParent()
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("timed out waiting for parent context to be canceled")
+	}
+}
+
+func TestNotifyContextPrematureCancelParent(t *testing.T) {
+	parent, cancelParent := context.WithCancel(context.Background())
+	defer cancelParent()
+
+	cancelParent() // Prematurely cancel context before calling NotifyContext.
+	c, stop := NotifyContext(parent, syscall.SIGINT)
+	defer stop()
+
+	if want, got := "signal.NotifyContext(context.Background.WithCancel, [interrupt])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("timed out waiting for parent context to be canceled")
+	}
+}
+
+func TestNotifyContextSimultaneousNotifications(t *testing.T) {
+	c, stop := NotifyContext(context.Background(), syscall.SIGINT)
+	defer stop()
+
+	if want, got := "signal.NotifyContext(context.Background, [interrupt])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+
+	var wg sync.WaitGroup
+	n := 10
+	wg.Add(n)
+	for i := 0; i < n; i++ {
+		go func() {
+			syscall.Kill(syscall.Getpid(), syscall.SIGINT)
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("expected context to be canceled")
+	}
+}
+
+func TestNotifyContextSimultaneousStop(t *testing.T) {
+	c, stop := NotifyContext(context.Background(), syscall.SIGINT)
+	defer stop()
+
+	if want, got := "signal.NotifyContext(context.Background, [interrupt])", fmt.Sprint(c); want != got {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+
+	var wg sync.WaitGroup
+	n := 10
+	wg.Add(n)
+	for i := 0; i < n; i++ {
+		go func() {
+			stop()
+			wg.Done()
+		}()
+	}
+	wg.Wait()
+	select {
+	case <-c.Done():
+		if got := c.Err(); got != context.Canceled {
+			t.Errorf("c.Err() = %q, want %q", got, context.Canceled)
+		}
+	case <-time.After(time.Second):
+		t.Errorf("expected context to be canceled")
+	}
+}
+
+func TestNotifyContextStringer(t *testing.T) {
+	parent, cancelParent := context.WithCancel(context.Background())
+	defer cancelParent()
+	c, stop := NotifyContext(parent, syscall.SIGHUP, syscall.SIGINT, syscall.SIGTERM)
+	defer stop()
+
+	want := `signal.NotifyContext(context.Background.WithCancel, [hangup interrupt terminated])`
+	if got := fmt.Sprint(c); got != want {
+		t.Errorf("c.String() = %q, want %q", got, want)
+	}
+}