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@abhinav @kriskowal @prashantv
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// Copyright (c) 2016 Uber Technologies, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
package ratelimit // import "go.uber.org/ratelimit"
import (
"sync"
"time"
"go.uber.org/ratelimit/internal/clock"
)
// Note: This file is inspired by:
// https://github.com/prashantv/go-bench/blob/master/ratelimit
// Limiter is used to rate-limit some process, possibly across goroutines.
// The process is expected to call Take() before every iteration, which
// may block to throttle the goroutine.
type Limiter interface {
// Take should block to make sure that the RPS is met.
Take() time.Time
}
// Clock is the minimum necessary interface to instantiate a rate limiter with
// a clock or mock clock, compatible with clocks created using
// github.com/andres-erbsen/clock.
type Clock interface {
Now() time.Time
Sleep(time.Duration)
}
type limiter struct {
sync.Mutex
last time.Time
sleepFor time.Duration
perRequest time.Duration
maxSlack time.Duration
clock Clock
}
// Option configures a Limiter.
type Option func(l *limiter)
// New returns a Limiter that will limit to the given RPS.
func New(rate int, opts ...Option) Limiter {
l := &limiter{
perRequest: time.Second / time.Duration(rate),
maxSlack: -10 * time.Second / time.Duration(rate),
}
for _, opt := range opts {
opt(l)
}
if l.clock == nil {
l.clock = clock.New()
}
return l
}
// WithClock returns an option for ratelimit.New that provides an alternate
// Clock implementation, typically a mock Clock for testing.
func WithClock(clock Clock) Option {
return func(l *limiter) {
l.clock = clock
}
}
// WithoutSlack is an option for ratelimit.New that initializes the limiter
// without any initial tolerance for bursts of traffic.
var WithoutSlack Option = withoutSlackOption
func withoutSlackOption(l *limiter) {
l.maxSlack = 0
}
// Take blocks to ensure that the time spent between multiple
// Take calls is on average time.Second/rate.
func (t *limiter) Take() time.Time {
t.Lock()
defer t.Unlock()
now := t.clock.Now()
// If this is our first request, then we allow it.
if t.last.IsZero() {
t.last = now
return t.last
}
// sleepFor calculates how much time we should sleep based on
// the perRequest budget and how long the last request took.
// Since the request may take longer than the budget, this number
// can get negative, and is summed across requests.
t.sleepFor += t.perRequest - now.Sub(t.last)
// We shouldn't allow sleepFor to get too negative, since it would mean that
// a service that slowed down a lot for a short period of time would get
// a much higher RPS following that.
if t.sleepFor < t.maxSlack {
t.sleepFor = t.maxSlack
}
// If sleepFor is positive, then we should sleep now.
if t.sleepFor > 0 {
t.clock.Sleep(t.sleepFor)
t.last = now.Add(t.sleepFor)
t.sleepFor = 0
} else {
t.last = now
}
return t.last
}
type unlimited struct{}
// NewUnlimited returns a RateLimiter that is not limited.
func NewUnlimited() Limiter {
return unlimited{}
}
func (unlimited) Take() time.Time {
return time.Now()
}
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