7c9314f231
* swarm: propagate ctx, enable opentracing * swarm/tracing: log error when tracing is misconfigured
78 lines
2.9 KiB
Go
78 lines
2.9 KiB
Go
// Copyright (c) 2017 Uber Technologies, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package utils
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import (
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"sync"
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"time"
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)
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// RateLimiter is a filter used to check if a message that is worth itemCost units is within the rate limits.
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type RateLimiter interface {
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CheckCredit(itemCost float64) bool
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}
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type rateLimiter struct {
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sync.Mutex
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creditsPerSecond float64
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balance float64
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maxBalance float64
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lastTick time.Time
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timeNow func() time.Time
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}
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// NewRateLimiter creates a new rate limiter based on leaky bucket algorithm, formulated in terms of a
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// credits balance that is replenished every time CheckCredit() method is called (tick) by the amount proportional
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// to the time elapsed since the last tick, up to max of creditsPerSecond. A call to CheckCredit() takes a cost
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// of an item we want to pay with the balance. If the balance exceeds the cost of the item, the item is "purchased"
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// and the balance reduced, indicated by returned value of true. Otherwise the balance is unchanged and return false.
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//
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// This can be used to limit a rate of messages emitted by a service by instantiating the Rate Limiter with the
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// max number of messages a service is allowed to emit per second, and calling CheckCredit(1.0) for each message
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// to determine if the message is within the rate limit.
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//
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// It can also be used to limit the rate of traffic in bytes, by setting creditsPerSecond to desired throughput
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// as bytes/second, and calling CheckCredit() with the actual message size.
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func NewRateLimiter(creditsPerSecond, maxBalance float64) RateLimiter {
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return &rateLimiter{
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creditsPerSecond: creditsPerSecond,
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balance: maxBalance,
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maxBalance: maxBalance,
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lastTick: time.Now(),
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timeNow: time.Now}
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}
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func (b *rateLimiter) CheckCredit(itemCost float64) bool {
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b.Lock()
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defer b.Unlock()
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// calculate how much time passed since the last tick, and update current tick
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currentTime := b.timeNow()
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elapsedTime := currentTime.Sub(b.lastTick)
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b.lastTick = currentTime
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// calculate how much credit have we accumulated since the last tick
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b.balance += elapsedTime.Seconds() * b.creditsPerSecond
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if b.balance > b.maxBalance {
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b.balance = b.maxBalance
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}
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// if we have enough credits to pay for current item, then reduce balance and allow
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if b.balance >= itemCost {
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b.balance -= itemCost
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return true
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}
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return false
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}
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