simplifies error handling, uses internal logger by default

handler.go

@@ -15,10 +15,9 @@
 package otel // import "go.opentelemetry.io/otel"
 
 import (
-	"log"
-	"os"
 	"sync"
-	"sync/atomic"
+
+	"go.opentelemetry.io/otel/internal/debug"
 )
 
 var (
@@ -26,79 +25,61 @@ var (
 	// throughout an OpenTelemetry instrumented project. When a user
 	// specified ErrorHandler is registered (`SetErrorHandler`) all calls to
 	// `Handle` and will be delegated to the registered ErrorHandler.
-	globalErrorHandler = defaultErrorHandler()
-
+	globalErrorHandler = &errorHandlerDelegate{
+		delegate: &defaultErrorHandler{},
+	}
 	// delegateErrorHandlerOnce ensures that a user provided ErrorHandler is
 	// only ever registered once.
 	delegateErrorHandlerOnce sync.Once
 
 	// Compile-time check that delegator implements ErrorHandler.
-	_ ErrorHandler = (*delegator)(nil)
+	_ ErrorHandler = (*errorHandlerDelegate)(nil)
+	_ ErrorHandler = (*defaultErrorHandler)(nil)
 )
 
-type holder struct {
-	eh ErrorHandler
+// errorHandlerDelegate is a box type to enable updating of all handlers returned by GetErrorHandler()
+type errorHandlerDelegate struct {
+	delegate ErrorHandler
 }
 
-func defaultErrorHandler() *atomic.Value {
-	v := &atomic.Value{}
-	v.Store(holder{eh: &delegator{l: log.New(os.Stderr, "", log.LstdFlags)}})
-	return v
+func (h *errorHandlerDelegate) setDelegate(d ErrorHandler) {
+	h.delegate = d
 }
 
-// delegator logs errors if no delegate is set, otherwise they are delegated.
-type delegator struct {
-	delegate atomic.Value
-
-	l *log.Logger
-}
-
-// setDelegate sets the ErrorHandler delegate.
-func (h *delegator) setDelegate(d ErrorHandler) {
-	// It is critical this is guarded with delegateErrorHandlerOnce, if it is
-	// called again with a different concrete type it will panic.
-	h.delegate.Store(d)
-}
-
-// Handle logs err if no delegate is set, otherwise it is delegated.
-func (h *delegator) Handle(err error) {
-	if d := h.delegate.Load(); d != nil {
-		d.(ErrorHandler).Handle(err)
+// Handle handles any error deemed irremediable by an OpenTelemetry component.
+func (h *errorHandlerDelegate) Handle(err error) {
+	if h == nil {
 		return
 	}
-	h.l.Print(err)
+	h.delegate.Handle(err)
 }
 
+// defaultErrorHandler utilizes the internal logger to manage the messages.
+type defaultErrorHandler struct{}
+
+func (h *defaultErrorHandler) Handle(err error) {
+	debug.Error(err, "")
+}
+
+// DiscardErrorHandler drops all errors.
+// Use `SetErrorHandler(DiscardErrorHandler{})` to disable error handling
+type DiscardErrorHandler struct{}
+
+func (DiscardErrorHandler) Handle(error) {}
+
 // GetErrorHandler returns the global ErrorHandler instance.
 //
 // The default ErrorHandler instance returned will log all errors to STDERR
 // until an override ErrorHandler is set with SetErrorHandler. All
 // ErrorHandler returned prior to this will automatically forward errors to
 // the set instance instead of logging.
-//
-// Subsequent calls to SetErrorHandler after the first will not forward errors
-// to the new ErrorHandler for prior returned instances.
 func GetErrorHandler() ErrorHandler {
-	return globalErrorHandler.Load().(holder).eh
+	return globalErrorHandler
 }
 
 // SetErrorHandler sets the global ErrorHandler to h.
-//
-// The first time this is called all ErrorHandler previously returned from
-// GetErrorHandler will send errors to h instead of the default logging
-// ErrorHandler. Subsequent calls will set the global ErrorHandler, but not
-// delegate errors to h.
 func SetErrorHandler(h ErrorHandler) {
-	delegateErrorHandlerOnce.Do(func() {
-		current := GetErrorHandler()
-		if current == h {
-			return
-		}
-		if internalHandler, ok := current.(*delegator); ok {
-			internalHandler.setDelegate(h)
-		}
-	})
-	globalErrorHandler.Store(holder{eh: h})
+	globalErrorHandler.setDelegate(h)
 }
 
 // Handle is a convenience function for ErrorHandler().Handle(err)