remove SetLogger, add operational logs (#103)

The NewConfig function provides a hook for replacing the logger, which is
the best place to do this, since it will capture the writer init message.

Add a few extra log lines to capture key operational details related to
startup and shutdown.

README.md

@@ -79,6 +79,7 @@ func getNextRequest() *Request {
 
 func main() {
 	commonTags := map[string]string{"nf.platform": "my_platform", "process_name": "my_process"}
+	// if desired, replace the logger with a custom one, using the third parameter here:
 	config, _ := spectator.NewConfig("", commonTags, nil)
 
 	registry, _ := spectator.NewRegistry(config)

spectator/registry.go

@@ -22,7 +22,6 @@ type Meter interface {
 // Registry is the main entry point for interacting with the Spectator library.
 type Registry interface {
 	GetLogger() logger.Logger
-	SetLogger(logger logger.Logger)
 	NewId(name string, tags map[string]string) *meter.Id
 	AgeGauge(name string, tags map[string]string) *meter.AgeGauge
 	AgeGaugeWithId(id *meter.Id) *meter.AgeGauge
@@ -62,11 +61,11 @@ type spectatordRegistry struct {
 // NewRegistry generates a new registry from a passed Config created through NewConfig.
 func NewRegistry(config *Config) (Registry, error) {
 	if config == nil {
-		return nil, fmt.Errorf("config cannot be nil")
+		return nil, fmt.Errorf("Config cannot be nil")
 	}
 
 	if config.location == "" {
-		// Config was not created using NewConfig. Set a default config instead of using the passed one
+		// Config was not created using NewConfig. Set a default config instead of using the passed one.
 		config, _ = NewConfig("", nil, nil)
 	}
 
@@ -75,6 +74,8 @@ func NewRegistry(config *Config) (Registry, error) {
 		return nil, err
 	}
 
+	config.log.Infof("Create Registry with extra commonTags=%v", config.commonTags)
+
 	r := &spectatordRegistry{
 		config: config,
 		writer: newWriter,
@@ -89,11 +90,6 @@ func (r *spectatordRegistry) GetLogger() logger.Logger {
 	return r.logger
 }
 
-// SetLogger overrides the internal logger.
-func (r *spectatordRegistry) SetLogger(logger logger.Logger) {
-	r.logger = logger
-}
-
 // NewId calls meters.NewId() and adds the commonTags registered in the config.
 func (r *spectatordRegistry) NewId(name string, tags map[string]string) *meter.Id {
 	newId := meter.NewId(name, tags)
@@ -198,9 +194,9 @@ func (r *spectatordRegistry) GetWriter() writer.Writer {
 }
 
 func (r *spectatordRegistry) Close() {
+	r.GetLogger().Infof("Close Registry Writer")
 	err := r.writer.Close()
-
 	if err != nil {
-		r.GetLogger().Errorf("Error closing writer: %v", err)
+		r.GetLogger().Errorf("Error closing Registry Writer: %v", err)
 	}
 }