Implement telegraf collecting stats on itself

closes #1348

selfstat/selfstat.go

@@ -0,0 +1,169 @@
+// selfstat is a package for tracking and collecting internal statistics
+// about telegraf. Metrics can be registered using this package, and then
+// incremented or set within your code. If the inputs.internal plugin is enabled,
+// then all registered stats will be collected as they would by any other input
+// plugin.
+package selfstat
+
+import (
+	"hash/fnv"
+	"log"
+	"sort"
+	"sync"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+)
+
+var (
+	registry *rgstry
+)
+
+// Stat is an interface for dealing with telegraf statistics collected
+// on itself.
+type Stat interface {
+	// Name is the name of the measurement
+	Name() string
+
+	// FieldName is the name of the measurement field
+	FieldName() string
+
+	// Tags is a tag map. Each time this is called a new map is allocated.
+	Tags() map[string]string
+
+	// Key is the unique measurement+tags key of the stat.
+	Key() uint64
+
+	// Incr increments a regular stat by 'v'.
+	// in the case of a timing stat, increment adds the timing to the cache.
+	Incr(v int64)
+
+	// Set sets a regular stat to 'v'.
+	// in the case of a timing stat, set adds the timing to the cache.
+	Set(v int64)
+
+	// Get gets the value of the stat. In the case of timings, this returns
+	// an average value of all timings received since the last call to Get().
+	// If no timings were received, it returns the previous value.
+	Get() int64
+}
+
+// Register registers the given measurement, field, and tags in the selfstat
+// registry. If given an identical measurement, it will return the stat that's
+// already been registered.
+//
+// The returned Stat can be incremented by the consumer of Register(), and it's
+// value will be returned as a telegraf metric when Metrics() is called.
+func Register(measurement, field string, tags map[string]string) Stat {
+	return registry.register(&stat{
+		measurement: "internal_" + measurement,
+		field:       field,
+		tags:        tags,
+	})
+}
+
+// RegisterTiming registers the given measurement, field, and tags in the selfstat
+// registry. If given an identical measurement, it will return the stat that's
+// already been registered.
+//
+// Timing stats differ from regular stats in that they accumulate multiple
+// "timings" added to them, and will return the average when Get() is called.
+// After Get() is called, the average is cleared and the next timing returned
+// from Get() will only reflect timings added since the previous call to Get().
+// If Get() is called without receiving any new timings, then the previous value
+// is used.
+//
+// In other words, timings are an averaged metric that get cleared on each call
+// to Get().
+//
+// The returned Stat can be incremented by the consumer of Register(), and it's
+// value will be returned as a telegraf metric when Metrics() is called.
+func RegisterTiming(measurement, field string, tags map[string]string) Stat {
+	return registry.register(&timingStat{
+		measurement: "internal_" + measurement,
+		field:       field,
+		tags:        tags,
+	})
+}
+
+// Metrics returns all registered stats as telegraf metrics.
+func Metrics() []telegraf.Metric {
+	registry.mu.Lock()
+	now := time.Now()
+	metrics := make([]telegraf.Metric, len(registry.stats))
+	i := 0
+	for _, stats := range registry.stats {
+		if len(stats) > 0 {
+			var tags map[string]string
+			var name string
+			fields := map[string]interface{}{}
+			j := 0
+			for fieldname, stat := range stats {
+				if j == 0 {
+					tags = stat.Tags()
+					name = stat.Name()
+				}
+				fields[fieldname] = stat.Get()
+				j++
+			}
+			metric, err := metric.New(name, tags, fields, now)
+			if err != nil {
+				log.Printf("E! Error creating selfstat metric: %s", err)
+				continue
+			}
+			metrics[i] = metric
+			i++
+		}
+	}
+	registry.mu.Unlock()
+	return metrics
+}
+
+type rgstry struct {
+	stats map[uint64]map[string]Stat
+	mu    sync.Mutex
+}
+
+func (r *rgstry) register(s Stat) Stat {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if stats, ok := r.stats[s.Key()]; ok {
+		// measurement exists
+		if stat, ok := stats[s.FieldName()]; ok {
+			// field already exists, so don't create a new one
+			return stat
+		}
+		r.stats[s.Key()][s.FieldName()] = s
+		return s
+	} else {
+		// creating a new unique metric
+		r.stats[s.Key()] = map[string]Stat{s.FieldName(): s}
+		return s
+	}
+}
+
+func key(measurement string, tags map[string]string) uint64 {
+	h := fnv.New64a()
+	h.Write([]byte(measurement))
+
+	tmp := make([]string, len(tags))
+	i := 0
+	for k, v := range tags {
+		tmp[i] = k + v
+		i++
+	}
+	sort.Strings(tmp)
+
+	for _, s := range tmp {
+		h.Write([]byte(s))
+	}
+
+	return h.Sum64()
+}
+
+func init() {
+	registry = &rgstry{
+		stats: make(map[uint64]map[string]Stat),
+	}
+}