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