mirror of https://github.com/tailscale/tailscale/
tstime/rate: new package
This is a simplified rate limiter geared for exactly our needs: A fast, mono.Time-based rate limiter for use in tstun. It was generated by stripping down the x/time/rate rate limiter to just our needs and switching it to use mono.Time. It removes one time.Now call per packet. Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>josh/debug-flake
Josh Bleecher Snyder
3 years ago
committed by
Josh Bleecher Snyder
parent
f6e833748b
commit
9da4181606
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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This is a modified, simplified version of code from golang.org/x/time/rate.
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package rate provides a rate limiter.
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package rate
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import (
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"sync"
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"time"
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"tailscale.com/tstime/mono"
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)
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// Limit defines the maximum frequency of some events.
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// Limit is represented as number of events per second.
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// A zero Limit is invalid.
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type Limit float64
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// Every converts a minimum time interval between events to a Limit.
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func Every(interval time.Duration) Limit {
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if interval <= 0 {
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panic("invalid interval")
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}
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return 1 / Limit(interval.Seconds())
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}
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// A Limiter controls how frequently events are allowed to happen.
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// It implements a "token bucket" of size b, initially full and refilled
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// at rate r tokens per second.
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// Informally, in any large enough time interval, the Limiter limits the
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// rate to r tokens per second, with a maximum burst size of b events.
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// See https://en.wikipedia.org/wiki/Token_bucket for more about token buckets.
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// Use NewLimiter to create non-zero Limiters.
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type Limiter struct {
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limit Limit
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burst float64
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mu sync.Mutex // protects following fields
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tokens float64 // number of tokens currently in bucket
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last mono.Time // the last time the limiter's tokens field was updated
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}
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// NewLimiter returns a new Limiter that allows events up to rate r and permits
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// bursts of at most b tokens.
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func NewLimiter(r Limit, b int) *Limiter {
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if b < 1 {
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panic("bad burst, must be at least 1")
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}
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return &Limiter{limit: r, burst: float64(b)}
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}
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// AllowN reports whether an event may happen now.
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func (lim *Limiter) Allow() bool {
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return lim.allow(mono.Now())
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}
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func (lim *Limiter) allow(now mono.Time) bool {
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lim.mu.Lock()
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defer lim.mu.Unlock()
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// If time has moved backwards, look around awkwardly and pretend nothing happened.
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if now.Before(lim.last) {
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lim.last = now
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}
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// Calculate the new number of tokens available due to the passage of time.
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elapsed := now.Sub(lim.last)
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tokens := lim.tokens + float64(lim.limit)*elapsed.Seconds()
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if tokens > lim.burst {
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tokens = lim.burst
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}
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// Consume a token.
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tokens--
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// Update state.
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ok := tokens >= 0
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if ok {
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lim.last = now
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lim.tokens = tokens
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}
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return ok
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}
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@ -0,0 +1,246 @@
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// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// This is a modified, simplified version of code from golang.org/x/time/rate.
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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:build go1.7
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// +build go1.7
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package rate
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import (
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"context"
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"math"
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"runtime"
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"sync"
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"sync/atomic"
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"testing"
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"time"
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"tailscale.com/tstime/mono"
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)
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func closeEnough(a, b Limit) bool {
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return (math.Abs(float64(a)/float64(b)) - 1.0) < 1e-9
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}
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func TestEvery(t *testing.T) {
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cases := []struct {
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interval time.Duration
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lim Limit
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}{
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{1 * time.Nanosecond, Limit(1e9)},
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{1 * time.Microsecond, Limit(1e6)},
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{1 * time.Millisecond, Limit(1e3)},
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{10 * time.Millisecond, Limit(100)},
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{100 * time.Millisecond, Limit(10)},
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{1 * time.Second, Limit(1)},
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{2 * time.Second, Limit(0.5)},
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{time.Duration(2.5 * float64(time.Second)), Limit(0.4)},
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{4 * time.Second, Limit(0.25)},
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{10 * time.Second, Limit(0.1)},
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{time.Duration(math.MaxInt64), Limit(1e9 / float64(math.MaxInt64))},
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}
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for _, tc := range cases {
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lim := Every(tc.interval)
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if !closeEnough(lim, tc.lim) {
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t.Errorf("Every(%v) = %v want %v", tc.interval, lim, tc.lim)
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}
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}
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}
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const (
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d = 100 * time.Millisecond
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)
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var (
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t0 = mono.Now()
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t1 = t0.Add(time.Duration(1) * d)
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t2 = t0.Add(time.Duration(2) * d)
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t3 = t0.Add(time.Duration(3) * d)
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t4 = t0.Add(time.Duration(4) * d)
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t5 = t0.Add(time.Duration(5) * d)
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t9 = t0.Add(time.Duration(9) * d)
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)
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type allow struct {
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t mono.Time
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ok bool
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}
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func run(t *testing.T, lim *Limiter, allows []allow) {
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t.Helper()
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for i, allow := range allows {
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ok := lim.allow(allow.t)
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if ok != allow.ok {
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t.Errorf("step %d: lim.AllowN(%v) = %v want %v",
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i, allow.t, ok, allow.ok)
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}
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}
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}
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func TestLimiterBurst1(t *testing.T) {
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run(t, NewLimiter(10, 1), []allow{
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{t0, true},
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{t0, false},
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{t0, false},
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{t1, true},
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{t1, false},
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{t1, false},
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{t2, true},
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{t2, false},
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})
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}
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func TestLimiterJumpBackwards(t *testing.T) {
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run(t, NewLimiter(10, 3), []allow{
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{t1, true}, // start at t1
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{t0, true}, // jump back to t0, two tokens remain
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{t0, true},
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{t0, false},
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{t0, false},
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{t1, true}, // got a token
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{t1, false},
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{t1, false},
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{t2, true}, // got another token
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{t2, false},
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{t2, false},
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})
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}
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// Ensure that tokensFromDuration doesn't produce
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// rounding errors by truncating nanoseconds.
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// See golang.org/issues/34861.
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func TestLimiter_noTruncationErrors(t *testing.T) {
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if !NewLimiter(0.7692307692307693, 1).Allow() {
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t.Fatal("expected true")
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}
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}
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func TestSimultaneousRequests(t *testing.T) {
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const (
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limit = 1
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burst = 5
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numRequests = 15
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)
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var (
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wg sync.WaitGroup
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numOK = uint32(0)
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)
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// Very slow replenishing bucket.
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lim := NewLimiter(limit, burst)
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// Tries to take a token, atomically updates the counter and decreases the wait
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// group counter.
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f := func() {
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defer wg.Done()
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if ok := lim.Allow(); ok {
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atomic.AddUint32(&numOK, 1)
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}
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}
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wg.Add(numRequests)
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for i := 0; i < numRequests; i++ {
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go f()
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}
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wg.Wait()
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if numOK != burst {
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t.Errorf("numOK = %d, want %d", numOK, burst)
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}
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}
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func TestLongRunningQPS(t *testing.T) {
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if testing.Short() {
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t.Skip("skipping in short mode")
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}
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if runtime.GOOS == "openbsd" {
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t.Skip("low resolution time.Sleep invalidates test (golang.org/issue/14183)")
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return
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}
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// The test runs for a few seconds executing many requests and then checks
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// that overall number of requests is reasonable.
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const (
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limit = 100
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burst = 100
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)
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var numOK = int32(0)
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lim := NewLimiter(limit, burst)
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var wg sync.WaitGroup
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f := func() {
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if ok := lim.Allow(); ok {
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atomic.AddInt32(&numOK, 1)
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}
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wg.Done()
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}
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start := time.Now()
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end := start.Add(5 * time.Second)
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for time.Now().Before(end) {
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wg.Add(1)
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go f()
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// This will still offer ~500 requests per second, but won't consume
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// outrageous amount of CPU.
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time.Sleep(2 * time.Millisecond)
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}
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wg.Wait()
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elapsed := time.Since(start)
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ideal := burst + (limit * float64(elapsed) / float64(time.Second))
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// We should never get more requests than allowed.
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if want := int32(ideal + 1); numOK > want {
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t.Errorf("numOK = %d, want %d (ideal %f)", numOK, want, ideal)
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}
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// We should get very close to the number of requests allowed.
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if want := int32(0.999 * ideal); numOK < want {
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t.Errorf("numOK = %d, want %d (ideal %f)", numOK, want, ideal)
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}
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}
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type request struct {
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t time.Time
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n int
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act time.Time
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ok bool
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}
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// dFromDuration converts a duration to a multiple of the global constant d
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func dFromDuration(dur time.Duration) int {
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// Adding a millisecond to be swallowed by the integer division
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// because we don't care about small inaccuracies
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return int((dur + time.Millisecond) / d)
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}
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// dSince returns multiples of d since t0
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func dSince(t mono.Time) int {
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return dFromDuration(t.Sub(t0))
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}
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type wait struct {
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name string
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ctx context.Context
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n int
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delay int // in multiples of d
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nilErr bool
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}
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func BenchmarkAllowN(b *testing.B) {
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lim := NewLimiter(Every(1*time.Second), 1)
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now := mono.Now()
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b.ReportAllocs()
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b.ResetTimer()
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b.RunParallel(func(pb *testing.PB) {
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for pb.Next() {
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lim.allow(now)
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}
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})
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}
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