78 lines
2.9 KiB
Go
78 lines
2.9 KiB
Go
|
// 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
|
||
|
|
}
|