Implement telegraf collecting stats on itself

closes #1348

selfstat/timingStat.go

@@ -0,0 +1,66 @@
+package selfstat
+
+import (
+	"sync"
+)
+
+type timingStat struct {
+	measurement string
+	field       string
+	tags        map[string]string
+	key         uint64
+	v           int64
+	prev        int64
+	count       int64
+	mu          sync.Mutex
+}
+
+func (s *timingStat) Incr(v int64) {
+	s.mu.Lock()
+	s.v += v
+	s.count++
+	s.mu.Unlock()
+}
+
+func (s *timingStat) Set(v int64) {
+	s.Incr(v)
+}
+
+func (s *timingStat) Get() int64 {
+	var avg int64
+	s.mu.Lock()
+	if s.count > 0 {
+		s.prev, avg = s.v/s.count, s.v/s.count
+		s.v = 0
+		s.count = 0
+	} else {
+		avg = s.prev
+	}
+	s.mu.Unlock()
+	return avg
+}
+
+func (s *timingStat) Name() string {
+	return s.measurement
+}
+
+func (s *timingStat) FieldName() string {
+	return s.field
+}
+
+// Tags returns a copy of the timingStat's tags.
+// NOTE this allocates a new map every time it is called.
+func (s *timingStat) Tags() map[string]string {
+	m := make(map[string]string, len(s.tags))
+	for k, v := range s.tags {
+		m[k] = v
+	}
+	return m
+}
+
+func (s *timingStat) Key() uint64 {
+	if s.key == 0 {
+		s.key = key(s.measurement, s.tags)
+	}
+	return s.key
+}