update

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/open-policy-agent/opa/util/backoff.go

@@ -0,0 +1,42 @@
+// Copyright 2018 The OPA Authors.  All rights reserved.
+// Use of this source code is governed by an Apache2
+// license that can be found in the LICENSE file.
+
+package util
+
+import (
+	"math/rand"
+	"time"
+)
+
+// DefaultBackoff returns a delay with an exponential backoff based on the
+// number of retries.
+func DefaultBackoff(base, max float64, retries int) time.Duration {
+	return Backoff(base, max, .2, 1.6, retries)
+}
+
+// Backoff returns a delay with an exponential backoff based on the number of
+// retries. Same algorithm used in gRPC.
+func Backoff(base, max, jitter, factor float64, retries int) time.Duration {
+	if retries == 0 {
+		return 0
+	}
+
+	backoff, max := float64(base), float64(max)
+	for backoff < max && retries > 0 {
+		backoff *= factor
+		retries--
+	}
+	if backoff > max {
+		backoff = max
+	}
+
+	// Randomize backoff delays so that if a cluster of requests start at
+	// the same time, they won't operate in lockstep.
+	backoff *= 1 + jitter*(rand.Float64()*2-1)
+	if backoff < 0 {
+		return 0
+	}
+
+	return time.Duration(backoff)
+}