Fix WrapProcess for Ring and Cluster. Add better example.

example_instrumentation_test.go

@@ -0,0 +1,59 @@
+package redis_test
+
+import (
+	"fmt"
+	"sync/atomic"
+	"time"
+
+	redis "gopkg.in/redis.v5"
+)
+
+func Example_instrumentation() {
+	ring := redis.NewRing(&redis.RingOptions{
+		Addrs: map[string]string{
+			"shard1": ":6379",
+		},
+	})
+	ring.ForEachShard(func(client *redis.Client) error {
+		wrapRedisProcess(client)
+		return nil
+	})
+
+	for {
+		ring.Ping()
+	}
+}
+
+func wrapRedisProcess(client *redis.Client) {
+	const precision = time.Microsecond
+	var count, avgDur uint32
+
+	go func() {
+		for _ = range time.Tick(3 * time.Second) {
+			n := atomic.LoadUint32(&count)
+			dur := time.Duration(atomic.LoadUint32(&avgDur)) * precision
+			fmt.Printf("%s: processed=%d avg_dur=%s\n", client, n, dur)
+		}
+	}()
+
+	client.WrapProcess(func(oldProcess func(redis.Cmder) error) func(redis.Cmder) error {
+		return func(cmd redis.Cmder) error {
+			start := time.Now()
+			err := oldProcess(cmd)
+			dur := time.Since(start)
+
+			const decay = float64(1) / 100
+			ms := float64(dur / precision)
+			for {
+				avg := atomic.LoadUint32(&avgDur)
+				newAvg := uint32((1-decay)*float64(avg) + decay*ms)
+				if atomic.CompareAndSwapUint32(&avgDur, avg, newAvg) {
+					break
+				}
+			}
+			atomic.AddUint32(&count, 1)
+
+			return err
+		}
+	})
+}