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()
-}

build/logrotator.go

@@ -14,10 +14,6 @@ import (
 // RotatingLogWriter is a wrapper around the LogWriter that supports log file
 // rotation.
 type RotatingLogWriter struct {
-	// GenSubLogger is a function that returns a new logger for a subsystem
-	// belonging to the current RotatingLogWriter.
-	GenSubLogger func(string) btclog.Logger
-
 	logWriter *LogWriter
 
 	backendLog *btclog.Backend
@@ -39,16 +35,19 @@ func NewRotatingLogWriter() *RotatingLogWriter {
 	logWriter := &LogWriter{}
 	backendLog := btclog.NewBackend(logWriter)
 	return &RotatingLogWriter{
-		GenSubLogger: func(tag string) btclog.Logger {
-			logger := backendLog.Logger(tag)
-			return NewShutdownLogger(logger)
-		},
 		logWriter:        logWriter,
 		backendLog:       backendLog,
 		subsystemLoggers: SubLoggers{},
 	}
 }
 
+// GenSubLogger creates a new sublogger. A shutdown callback function
+// is provided to be able to shutdown in case of a critical error.
+func (r *RotatingLogWriter) GenSubLogger(tag string, shutdown func()) btclog.Logger {
+	logger := r.backendLog.Logger(tag)
+	return NewShutdownLogger(logger, shutdown)
+}
+
 // RegisterSubLogger registers a new subsystem logger.
 func (r *RotatingLogWriter) RegisterSubLogger(subsystem string,
 	logger btclog.Logger) {