dcrd: Simplify shutdown signal handling logic sync.

Upstream commit 044a11c.

dcrd.go

@@ -41,12 +41,14 @@ func dcrdMain(serverChan chan<- *server) error {
 	cfg = tcfg
 	defer backendLog.Flush()
 
-	interrupted := interruptListener()
+	// Get a channel that will be closed when a shutdown signal has been
+	// triggered either from an OS signal such as SIGINT (Ctrl+C) or from
+	// another subsystem such as the RPC server.
+	interruptedChan := interruptListener()
 	defer dcrdLog.Info("Shutdown complete")
 
-	// Show version at startup.
+	// Show version and home dir at startup.
 	dcrdLog.Infof("Version %s", version())
-	// Show dcrd home dir location
 	dcrdLog.Infof("Home dir: %s", cfg.HomeDir)
 
 	// Enable http profiling server if requested.
@@ -106,11 +108,8 @@ func dcrdMain(serverChan chan<- *server) error {
 		go drainOutgoingPipeMessages()
 	}
 
-	if interruptRequested(interrupted) {
-		return nil
-	}
-
-	if interruptRequested(interrupted) {
+	// Return now if an interrupt signal was triggered.
+	if interruptRequested(interruptedChan) {
 		return nil
 	}
 
@@ -122,12 +121,14 @@ func dcrdMain(serverChan chan<- *server) error {
 		return err
 	}
 	defer func() {
+		// Ensure the database is sync'd and closed on shutdown.
 		lifetimeNotifier.notifyShutdownEvent(lifetimeEventDBOpen)
 		dcrdLog.Infof("Gracefully shutting down the database...")
 		db.Close()
 	}()
 
-	if interruptRequested(interrupted) {
+	// Return now if an interrupt signal was triggered.
+	if interruptRequested(interruptedChan) {
 		return nil
 	}
 
@@ -182,15 +183,16 @@ func dcrdMain(serverChan chan<- *server) error {
 		serverChan <- server
 	}
 
-	if interruptRequested(interrupted) {
+	if interruptRequested(interruptedChan) {
 		return nil
 	}
 
 	lifetimeNotifier.notifyStartupComplete()
 
 	// Wait until the interrupt signal is received from an OS signal or
-	// shutdown is requested through the RPC server.
-	<-interrupted
+	// shutdown is requested through one of the subsystems such as the RPC
+	// server.
+	<-interruptedChan
 	return nil
 }
 

service_windows.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2013-2014 The btcsuite developers
+// Copyright (c) 2013-2016 The btcsuite developers
 // Copyright (c) 2015-2016 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
@@ -86,12 +86,8 @@ loop:
 				// more commands while pending.
 				changes <- svc.Status{State: svc.StopPending}
 
-				// Signal the main function to exit if shutdown
-				// was not already requested.
-				select {
-				case shutdownRequestChannel <- struct{}{}:
-				default:
-				}
+				// Signal the main function to exit.
+				shutdownRequestChannel <- struct{}{}
 
 			default:
 				elog.Error(1, fmt.Sprintf("Unexpected control "+

signal.go

@@ -1,4 +1,4 @@
-// Copyright (c) 2013-2014 The btcsuite developers
+// Copyright (c) 2013-2016 The btcsuite developers
 // Copyright (c) 2015-2016 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
@@ -18,24 +18,41 @@ var shutdownRequestChannel = make(chan struct{})
 // shutdown.  This may be modified during init depending on the platform.
 var interruptSignals = []os.Signal{os.Interrupt}
 
-// interruptListener listens for SIGINT (Ctrl+C) signals and shutdown requests
-// from shutdownRequestChannel.  It returns a channel that is closed when either
-// signal is received.
+// interruptListener listens for OS Signals such as SIGINT (Ctrl+C) and shutdown
+// requests from shutdownRequestChannel.  It returns a channel that is closed
+// when either signal is received.
 func interruptListener() <-chan struct{} {
 	c := make(chan struct{})
-
 	go func() {
 		interruptChannel := make(chan os.Signal, 1)
 		signal.Notify(interruptChannel, interruptSignals...)
 
+		// Listen for initial shutdown signal and close the returned
+		// channel to notify the caller.
 		select {
 		case sig := <-interruptChannel:
-			dcrdLog.Infof("Received signal (%s).  Shutting down...", sig)
+			dcrdLog.Infof("Received signal (%s).  Shutting down...",
+				sig)
+
 		case <-shutdownRequestChannel:
 			dcrdLog.Infof("Shutdown requested.  Shutting down...")
 		}
-
 		close(c)
+
+		// Listen for repeated signals and display a message so the user
+		// knows the shutdown is in progress and the process is not
+		// hung.
+		for {
+			select {
+			case sig := <-interruptChannel:
+				dcrdLog.Infof("Received signal (%s).  Already "+
+					"shutting down...", sig)
+
+			case <-shutdownRequestChannel:
+				dcrdLog.Info("Shutdown requested.  Already " +
+					"shutting down...")
+			}
+		}
 	}()
 
 	return c
@@ -49,6 +66,7 @@ func interruptRequested(interrupted <-chan struct{}) bool {
 	case <-interrupted:
 		return true
 	default:
-		return false
 	}
+
+	return false
 }