signal: handle shutdown properly

This addresses issues related to the mobile lnd builds, where
calling `stopDaemon` and subsequently calling LndMobile's `Start`
results in crash.

build/log_shutdown.go

@@ -2,20 +2,21 @@ package build
 
 import (
 	"github.com/btcsuite/btclog"
-	"github.com/lightningnetwork/lnd/signal"
 )
 
 // ShutdownLogger wraps an existing logger with a shutdown function which will
 // be called on Critical/Criticalf to prompt shutdown.
 type ShutdownLogger struct {
 	btclog.Logger
+	shutdown func()
 }
 
 // NewShutdownLogger creates a shutdown logger for the log provided which will
 // use the signal package to request shutdown on critical errors.
-func NewShutdownLogger(logger btclog.Logger) *ShutdownLogger {
+func NewShutdownLogger(logger btclog.Logger, shutdown func()) *ShutdownLogger {
 	return &ShutdownLogger{
-		Logger: logger,
+		Logger:   logger,
+		shutdown: shutdown,
 	}
 }
 
@@ -26,6 +27,7 @@ func NewShutdownLogger(logger btclog.Logger) *ShutdownLogger {
 // Note: it is part of the btclog.Logger interface.
 func (s *ShutdownLogger) Criticalf(format string, params ...interface{}) {
 	s.Logger.Criticalf(format, params...)
+	s.Logger.Info("Sending request for shutdown")
 	s.shutdown()
 }
 
@@ -36,18 +38,6 @@ func (s *ShutdownLogger) Criticalf(format string, params ...interface{}) {
 // Note: it is part of the btclog.Logger interface.
 func (s *ShutdownLogger) Critical(v ...interface{}) {
 	s.Logger.Critical(v)
+	s.Logger.Info("Sending request for shutdown")
 	s.shutdown()
 }
-
-// shutdown checks whether we are listening for interrupts, since a shutdown
-// request to the signal package will block if it is not running, and requests
-// shutdown if possible.
-func (s *ShutdownLogger) shutdown() {
-	if !signal.Listening() {
-		s.Logger.Info("Request for shutdown ignored")
-		return
-	}
-
-	s.Logger.Info("Sending request for shutdown")
-	signal.RequestShutdown()
-}