add ringlog

pkg/util/ringlog/ringlog.go

+package ringlog
+
+import (
+	"container/list"
+	"sync"
+)
+
+// RingLogger describes ring logger methods
+type RingLogger interface {
+	Insert(interface{})
+	Walk() []interface{}
+}
+
+// RingLog is a capped logger with fixed size
+type RingLog struct {
+	sync.RWMutex
+	size int
+	list *list.List
+}
+
+// New creates new Ring logger
+func New(size int) *RingLog {
+	r := RingLog{
+		list: list.New(),
+		size: size,
+	}
+
+	return &r
+}
+
+// Insert inserts new LogEntry into the ring logger
+func (r *RingLog) Insert(obj interface{}) {
+	r.Lock()
+	defer r.Unlock()
+
+	r.list.PushBack(obj)
+	if r.list.Len() > r.size {
+		r.list.Remove(r.list.Front())
+	}
+}
+
+// Walk dumps all the LogEntries from the Ring logger
+func (r *RingLog) Walk() []interface{} {
+	res := make([]interface{}, 0)
+
+	r.RLock()
+	defer r.RUnlock()
+
+	st := r.list.Front()
+	for i := 0; i < r.size; i++ {
+		if st == nil {
+			return res
+		}
+		res = append(res, st.Value)
+		st = st.Next()
+	}
+
+	return res
+}