Update shutdown signalling. (#293)

Bring in some updates from the signal handling code in other projects:

- Rename `signals` to more descriptive `interruptSignals`.
- Add SIGHUP to unix shutdown signals. Rename `signalsigterm.go` to `signal_unix.go` accordingly.
- Include extra detail in "Already shutting down..." messages log lines.
- Pass a shutdown func into `webapi.go` rather than a channel. It's more obvious how to invoke a func, whereas a channel can be used in multiple ways.

signal.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2013-2014 The btcsuite developers
+// Copyright (c) 2021 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -19,9 +20,9 @@ var shutdownRequestChannel = make(chan struct{})
 // withShutdownChannel are cancelled when this is closed.
 var shutdownSignaled = make(chan struct{})
 
-// signals defines the signals that are handled to do a clean shutdown.
+// interruptSignals defines the signals that are handled to do a clean shutdown.
-// Conditional compilation is used to also include SIGTERM on Unix.
+// Conditional compilation is used to also include SIGTERM and SIGHUP on Unix.
-var signals = []os.Signal{os.Interrupt}
+var interruptSignals = []os.Signal{os.Interrupt}
 
 // withShutdownCancel creates a copy of a context that is cancelled whenever
 // shutdown is invoked through an interrupt signal or from an JSON-RPC stop
@@ -36,7 +37,7 @@ func withShutdownCancel(ctx context.Context) context.Context {
 }
 
 // requestShutdown signals for starting the clean shutdown of the process
-// through an internal component (such as through the JSON-RPC stop request).
+// through an internal component.
 func requestShutdown() {
 	shutdownRequestChannel <- struct{}{}
 }
@@ -46,7 +47,7 @@ func requestShutdown() {
 // to be spawned in a new goroutine.
 func shutdownListener() {
 	interruptChannel := make(chan os.Signal, 1)
-	signal.Notify(interruptChannel, signals...)
+	signal.Notify(interruptChannel, interruptSignals...)
 
 	// Listen for the initial shutdown signal
 	select {
@@ -63,9 +64,10 @@ func shutdownListener() {
 	// been signaled.
 	for {
 		select {
-		case <-interruptChannel:
+		case sig := <-interruptChannel:
+			log.Infof("Received signal (%s). Already shutting down...", sig)
 		case <-shutdownRequestChannel:
+			log.Info("Shutdown requested. Already shutting down...")
 		}
-		log.Info("Shutdown signaled.  Already shutting down...")
 	}
 }

signal_unix.go

@@ -1,4 +1,5 @@
 // Copyright (c) 2016 The btcsuite developers
+// Copyright (c) 2021 The Decred developers
 // Use of this source code is governed by an ISC
 // license that can be found in the LICENSE file.
 
@@ -12,5 +13,9 @@ import (
 )
 
 func init() {
-	signals = []os.Signal{os.Interrupt, syscall.SIGTERM}
+	interruptSignals = []os.Signal{
+		os.Interrupt,
+		syscall.SIGTERM,
+		syscall.SIGHUP,
+	}
 }

vspd.go

@@ -104,7 +104,7 @@ func run(ctx context.Context) error {
 		MaxVoteChangeRecords: maxVoteChangeRecords,
 		VspdVersion:          version.String(),
 	}
-	err = webapi.Start(ctx, shutdownRequestChannel, &shutdownWg, cfg.Listen, db,
+	err = webapi.Start(ctx, requestShutdown, &shutdownWg, cfg.Listen, db,
 		dcrd, wallets, apiCfg)
 	if err != nil {
 		log.Errorf("Failed to initialize webapi: %v", err)

webapi/webapi.go

@@ -55,7 +55,7 @@ var addrGen *addressGenerator
 var signPrivKey ed25519.PrivateKey
 var signPubKey ed25519.PublicKey
 
-func Start(ctx context.Context, requestShutdownChan chan struct{}, shutdownWg *sync.WaitGroup,
+func Start(ctx context.Context, requestShutdown func(), shutdownWg *sync.WaitGroup,
 	listen string, vdb *database.VspDatabase, dcrd rpc.DcrdConnect, wallets rpc.WalletConnect, config Config) error {
 
 	cfg = config
@@ -137,7 +137,7 @@ func Start(ctx context.Context, requestShutdownChan chan struct{}, shutdownWg *s
 		// shutdown.
 		if err != nil && !errors.Is(err, http.ErrServerClosed) {
 			log.Errorf("Unexpected webserver error: %v", err)
-			requestShutdownChan <- struct{}{}
+			requestShutdown()
 		}
 	}()