Improve shutdown listener.

Copy shutdown listener logic from dcrd to:
  - improve OS signal handling.
  - add logging when a signal is received so it is clear why the process
    is being shutdown.

decred.go

@@ -11,10 +11,8 @@ import (
 	"net"
 	"net/netip"
 	"os"
-	"os/signal"
 	"path/filepath"
 	"sync"
-	"syscall"
 	"time"
 
 	"github.com/decred/dcrd/chaincfg/v3"
@@ -138,6 +136,8 @@ func creep(ctx context.Context, netParams *chaincfg.Params) {
 }
 
 func main() {
+	ctx := shutdownListener()
+
 	cfg, err := loadConfig()
 	if err != nil {
 		fmt.Fprintf(os.Stderr, "loadConfig: %v\n", err)
@@ -158,15 +158,6 @@ func main() {
 	}
 	amgr.AddAddresses([]netip.AddrPort{seeder})
 
-	ctx, shutdown := context.WithCancel(context.Background())
-	killSwitch := make(chan os.Signal, 1)
-	signal.Notify(killSwitch, os.Interrupt, syscall.SIGTERM, syscall.SIGHUP)
-	go func() {
-		<-killSwitch
-		log.Print("Shutting down...")
-		shutdown()
-	}()
-
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {

signal.go

@@ -0,0 +1,43 @@
+// Copyright (c) 2015-2023 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"log"
+	"os"
+	"os/signal"
+)
+
+// interruptSignals defines the default signals to catch in order to do a proper
+// shutdown. This may be modified during init depending on the platform.
+var interruptSignals = []os.Signal{os.Interrupt}
+
+// shutdownListener returns a context whose done channel will be closed when OS
+// signals such as SIGINT (Ctrl+C) are received.
+func shutdownListener() context.Context {
+	ctx, cancel := context.WithCancel(context.Background())
+	go func() {
+		interruptChannel := make(chan os.Signal, 1)
+		signal.Notify(interruptChannel, interruptSignals...)
+
+		// Listen for initial shutdown signal and cancel the context.
+		select {
+		case sig := <-interruptChannel:
+			log.Printf("Received signal (%s). Shutting down...", sig)
+			cancel()
+		case <-ctx.Done():
+		}
+
+		// Listen for repeated signals and display a message so the user knows
+		// the shutdown is in progress and the process is not hung.
+		for {
+			sig := <-interruptChannel
+			log.Printf("Received signal (%s). Already shutting down...", sig)
+		}
+	}()
+
+	return ctx
+}

signal_syscall.go

@@ -0,0 +1,15 @@
+// Copyright (c) 2021-2023 The Decred developers
+// Use of this source code is governed by an ISC
+// license that can be found in the LICENSE file.
+//
+//go:build windows || aix || android || darwin || dragonfly || freebsd || hurd || illumos || ios || linux || netbsd || openbsd || solaris
+
+package main
+
+import (
+	"syscall"
+)
+
+func init() {
+	interruptSignals = append(interruptSignals, syscall.SIGTERM, syscall.SIGHUP)
+}