swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

vendor/github.com/uber/jaeger-client-go/utils/rate_limiter.go

@@ -0,0 +1,77 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package utils
+
+import (
+	"sync"
+	"time"
+)
+
+// RateLimiter is a filter used to check if a message that is worth itemCost units is within the rate limits.
+type RateLimiter interface {
+	CheckCredit(itemCost float64) bool
+}
+
+type rateLimiter struct {
+	sync.Mutex
+
+	creditsPerSecond float64
+	balance          float64
+	maxBalance       float64
+	lastTick         time.Time
+
+	timeNow func() time.Time
+}
+
+// NewRateLimiter creates a new rate limiter based on leaky bucket algorithm, formulated in terms of a
+// credits balance that is replenished every time CheckCredit() method is called (tick) by the amount proportional
+// to the time elapsed since the last tick, up to max of creditsPerSecond. A call to CheckCredit() takes a cost
+// of an item we want to pay with the balance. If the balance exceeds the cost of the item, the item is "purchased"
+// and the balance reduced, indicated by returned value of true. Otherwise the balance is unchanged and return false.
+//
+// This can be used to limit a rate of messages emitted by a service by instantiating the Rate Limiter with the
+// max number of messages a service is allowed to emit per second, and calling CheckCredit(1.0) for each message
+// to determine if the message is within the rate limit.
+//
+// It can also be used to limit the rate of traffic in bytes, by setting creditsPerSecond to desired throughput
+// as bytes/second, and calling CheckCredit() with the actual message size.
+func NewRateLimiter(creditsPerSecond, maxBalance float64) RateLimiter {
+	return &rateLimiter{
+		creditsPerSecond: creditsPerSecond,
+		balance:          maxBalance,
+		maxBalance:       maxBalance,
+		lastTick:         time.Now(),
+		timeNow:          time.Now}
+}
+
+func (b *rateLimiter) CheckCredit(itemCost float64) bool {
+	b.Lock()
+	defer b.Unlock()
+	// calculate how much time passed since the last tick, and update current tick
+	currentTime := b.timeNow()
+	elapsedTime := currentTime.Sub(b.lastTick)
+	b.lastTick = currentTime
+	// calculate how much credit have we accumulated since the last tick
+	b.balance += elapsedTime.Seconds() * b.creditsPerSecond
+	if b.balance > b.maxBalance {
+		b.balance = b.maxBalance
+	}
+	// if we have enough credits to pay for current item, then reduce balance and allow
+	if b.balance >= itemCost {
+		b.balance -= itemCost
+		return true
+	}
+	return false
+}