internal, log: remove code for old unsupported go-versions (#28090)

log/handler.go

@@ -7,6 +7,7 @@ import (
 	"os"
 	"reflect"
 	"sync"
+	"sync/atomic"
 
 	"github.com/go-stack/stack"
 )
@@ -354,3 +355,21 @@ func (m muster) FileHandler(path string, fmtr Format) Handler {
 func (m muster) NetHandler(network, addr string, fmtr Format) Handler {
 	return must(NetHandler(network, addr, fmtr))
 }
+
+// swapHandler wraps another handler that may be swapped out
+// dynamically at runtime in a thread-safe fashion.
+type swapHandler struct {
+	handler atomic.Value
+}
+
+func (h *swapHandler) Log(r *Record) error {
+	return (*h.handler.Load().(*Handler)).Log(r)
+}
+
+func (h *swapHandler) Swap(newHandler Handler) {
+	h.handler.Store(&newHandler)
+}
+
+func (h *swapHandler) Get() Handler {
+	return *h.handler.Load().(*Handler)
+}