From c1b7112af8331d37e33be521d2d8baa552945971 Mon Sep 17 00:00:00 2001 From: Filippo Valsorda Date: Tue, 18 Nov 2025 17:19:04 +0100 Subject: [PATCH] os/signal: make NotifyContext cancel the context with a cause This is especially useful when combined with the nesting semantics of context.Cause, and with errgroup's use of CancelCauseFunc. For example, with the following code ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt) defer stop() serveGroup, ctx := errgroup.WithContext(ctx) calling context.Cause(ctx) after serveGroup.Wait() will return either "interrupt signal received" (if that happens first) or the error from serveGroup. Change-Id: Ie181f5f84269f6e39defdad2d5fd8ead6a6a6964 Reviewed-on: https://go-review.googlesource.com/c/go/+/721700 LUCI-TryBot-Result: Go LUCI Reviewed-by: Mark Freeman Reviewed-by: Sean Liao Auto-Submit: Filippo Valsorda Reviewed-by: Ian Lance Taylor Commit-Queue: Junyang Shao Reviewed-by: Junyang Shao --- .../99-minor/os/signal/notifycontext.md | 2 ++ src/os/signal/signal.go | 19 +++++++++---- src/os/signal/signal_test.go | 27 ++++++++++++++----- 3 files changed, 37 insertions(+), 11 deletions(-) create mode 100644 doc/next/6-stdlib/99-minor/os/signal/notifycontext.md diff --git a/doc/next/6-stdlib/99-minor/os/signal/notifycontext.md b/doc/next/6-stdlib/99-minor/os/signal/notifycontext.md new file mode 100644 index 0000000000..74b354b085 --- /dev/null +++ b/doc/next/6-stdlib/99-minor/os/signal/notifycontext.md @@ -0,0 +1,2 @@ +[NotifyContext] now cancels the returned context with [context.CancelCauseFunc] +and an error indicating which signal was received. diff --git a/src/os/signal/signal.go b/src/os/signal/signal.go index b9fe16baa5..70a91055e2 100644 --- a/src/os/signal/signal.go +++ b/src/os/signal/signal.go @@ -272,11 +272,14 @@ func process(sig os.Signal) { // the returned context. Future interrupts received will not trigger the default // (exit) behavior until the returned stop function is called. // +// If a signal causes the returned context to be canceled, calling +// [context.Cause] on it will return an error describing the signal. +// // The stop function releases resources associated with it, so code should // call stop as soon as the operations running in this Context complete and // signals no longer need to be diverted to the context. func NotifyContext(parent context.Context, signals ...os.Signal) (ctx context.Context, stop context.CancelFunc) { - ctx, cancel := context.WithCancel(parent) + ctx, cancel := context.WithCancelCause(parent) c := &signalCtx{ Context: ctx, cancel: cancel, @@ -287,8 +290,8 @@ func NotifyContext(parent context.Context, signals ...os.Signal) (ctx context.Co if ctx.Err() == nil { go func() { select { - case <-c.ch: - c.cancel() + case s := <-c.ch: + c.cancel(signalError(s.String() + " signal received")) case <-c.Done(): } }() @@ -299,13 +302,13 @@ func NotifyContext(parent context.Context, signals ...os.Signal) (ctx context.Co type signalCtx struct { context.Context - cancel context.CancelFunc + cancel context.CancelCauseFunc signals []os.Signal ch chan os.Signal } func (c *signalCtx) stop() { - c.cancel() + c.cancel(nil) Stop(c.ch) } @@ -333,3 +336,9 @@ func (c *signalCtx) String() string { buf = append(buf, ')') return string(buf) } + +type signalError string + +func (s signalError) Error() string { + return string(s) +} diff --git a/src/os/signal/signal_test.go b/src/os/signal/signal_test.go index 8d3f230178..8a3ba0e847 100644 --- a/src/os/signal/signal_test.go +++ b/src/os/signal/signal_test.go @@ -9,6 +9,7 @@ package signal import ( "bytes" "context" + "errors" "flag" "fmt" "internal/testenv" @@ -723,6 +724,9 @@ func TestNotifyContextNotifications(t *testing.T) { } wg.Wait() <-ctx.Done() + if got, want := context.Cause(ctx).Error(), "interrupt signal received"; got != want { + t.Errorf("context.Cause(ctx) = %q, want %q", got, want) + } fmt.Println("received SIGINT") // Sleep to give time to simultaneous signals to reach the process. // These signals must be ignored given stop() is not called on this code. @@ -797,11 +801,15 @@ func TestNotifyContextStop(t *testing.T) { if got := c.Err(); got != context.Canceled { t.Errorf("c.Err() = %q, want %q", got, context.Canceled) } + if got := context.Cause(c); got != context.Canceled { + t.Errorf("context.Cause(c.Err()) = %q, want %q", got, context.Canceled) + } } func TestNotifyContextCancelParent(t *testing.T) { - parent, cancelParent := context.WithCancel(context.Background()) - defer cancelParent() + parent, cancelParent := context.WithCancelCause(context.Background()) + parentCause := errors.New("parent canceled") + defer cancelParent(parentCause) c, stop := NotifyContext(parent, syscall.SIGINT) defer stop() @@ -809,18 +817,22 @@ func TestNotifyContextCancelParent(t *testing.T) { t.Errorf("c.String() = %q, want %q", got, want) } - cancelParent() + cancelParent(parentCause) <-c.Done() if got := c.Err(); got != context.Canceled { t.Errorf("c.Err() = %q, want %q", got, context.Canceled) } + if got := context.Cause(c); got != parentCause { + t.Errorf("context.Cause(c) = %q, want %q", got, parentCause) + } } func TestNotifyContextPrematureCancelParent(t *testing.T) { - parent, cancelParent := context.WithCancel(context.Background()) - defer cancelParent() + parent, cancelParent := context.WithCancelCause(context.Background()) + parentCause := errors.New("parent canceled") + defer cancelParent(parentCause) - cancelParent() // Prematurely cancel context before calling NotifyContext. + cancelParent(parentCause) // Prematurely cancel context before calling NotifyContext. c, stop := NotifyContext(parent, syscall.SIGINT) defer stop() @@ -832,6 +844,9 @@ func TestNotifyContextPrematureCancelParent(t *testing.T) { if got := c.Err(); got != context.Canceled { t.Errorf("c.Err() = %q, want %q", got, context.Canceled) } + if got := context.Cause(c); got != parentCause { + t.Errorf("context.Cause(c) = %q, want %q", got, parentCause) + } } func TestNotifyContextSimultaneousStop(t *testing.T) { -- 2.52.0