Restore int64 based atomic rate limiter (#94)

This limiter was introduced and merged in the following PR #85
Later @twelsh-aw found an issue with this implementation #90
So @rabbbit reverted this change in #91

Our tests did not detect this issue, so we have a separate PR #93 that enhances our tests approach to detect potential errors better.
With this PR, we want to restore the int64-based atomic rate limiter implementation as a non-default rate limiter and then check that #93 will detect the bug.
Right after it, we'll open a subsequent PR to fix this bug.

limiter_atomic_int64.go

@@ -0,0 +1,90 @@
+// Copyright (c) 2022 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 (
+	"time"
+
+	"sync/atomic"
+)
+
+type atomicInt64Limiter struct {
+	//lint:ignore U1000 Padding is unused but it is crucial to maintain performance
+	// of this rate limiter in case of collocation with other frequently accessed memory.
+	prepadding [64]byte // cache line size = 64; created to avoid false sharing.
+	state      int64    // unix nanoseconds of the next permissions issue.
+	//lint:ignore U1000 like prepadding.
+	postpadding [56]byte // cache line size - state size = 64 - 8; created to avoid false sharing.
+
+	perRequest time.Duration
+	maxSlack   time.Duration
+	clock      Clock
+}
+
+// newAtomicBased returns a new atomic based limiter.
+func newAtomicInt64Based(rate int, opts ...Option) *atomicInt64Limiter {
+	// TODO consider moving config building to the implementation
+	// independent code.
+	config := buildConfig(opts)
+	perRequest := config.per / time.Duration(rate)
+	l := &atomicInt64Limiter{
+		perRequest: perRequest,
+		maxSlack:   time.Duration(config.slack) * perRequest,
+		clock:      config.clock,
+	}
+	atomic.StoreInt64(&l.state, 0)
+	return l
+}
+
+// Take blocks to ensure that the time spent between multiple
+// Take calls is on average time.Second/rate.
+func (t *atomicInt64Limiter) Take() time.Time {
+	var (
+		newTimeOfNextPermissionIssue int64
+		now                          int64
+	)
+	for {
+		now = t.clock.Now().UnixNano()
+		timeOfNextPermissionIssue := atomic.LoadInt64(&t.state)
+
+		switch {
+		case timeOfNextPermissionIssue == 0:
+			// If this is our first request, then we allow it.
+			newTimeOfNextPermissionIssue = now
+		case now-timeOfNextPermissionIssue > int64(t.maxSlack):
+			// a lot of nanoseconds passed since the last Take call
+			// we will limit max accumulated time to maxSlack
+			newTimeOfNextPermissionIssue = now - int64(t.maxSlack)
+		default:
+			// calculate the time at which our permission was issued
+			newTimeOfNextPermissionIssue = timeOfNextPermissionIssue + int64(t.perRequest)
+		}
+
+		if atomic.CompareAndSwapInt64(&t.state, timeOfNextPermissionIssue, newTimeOfNextPermissionIssue) {
+			break
+		}
+	}
+	nanosToSleepUntilOurPermissionIsIssued := newTimeOfNextPermissionIssue - now
+	if nanosToSleepUntilOurPermissionIsIssued > 0 {
+		t.clock.Sleep(time.Duration(nanosToSleepUntilOurPermissionIsIssued))
+	}
+	return time.Unix(0, newTimeOfNextPermissionIssue)
+}

ratelimit_bench_test.go

@@ -14,8 +14,9 @@ func BenchmarkRateLimiter(b *testing.B) {
 	for _, procs := range []int{1, 4, 8, 16} {
 		runtime.GOMAXPROCS(procs)
 		for name, limiter := range map[string]Limiter{
-			"atomic": New(b.N * 10000000),
-			"mutex":  newMutexBased(b.N * 10000000),
+			"atomic":       newAtomicBased(b.N * 1000000000000),
+			"atomic_int64": newAtomicInt64Based(b.N * 1000000000000),
+			"mutex":        newMutexBased(b.N * 1000000000000),
 		} {
 			for ng := 1; ng < 16; ng++ {
 				runner(b, name, procs, ng, limiter, count)
@@ -47,7 +48,9 @@ func BenchmarkRateLimiter(b *testing.B) {
 }
 
 func runner(b *testing.B, name string, procs int, ng int, limiter Limiter, count *atomic.Int64) bool {
-	return b.Run(fmt.Sprintf("type:%s-procs:%d-goroutines:%d", name, procs, ng), func(b *testing.B) {
+	return b.Run(fmt.Sprintf("type:%s;max_procs:%d;goroutines:%d", name, procs, ng), func(b *testing.B) {
+		b.ReportAllocs()
+
 		var wg sync.WaitGroup
 		trigger := atomic.NewBool(true)
 		n := b.N

ratelimit_test.go

@@ -54,13 +54,23 @@ func runTest(t *testing.T, fn func(testRunner)) {
 				return newAtomicBased(rate, opts...)
 			},
 		},
+		{
+			name: "atomic_int64",
+			constructor: func(rate int, opts ...Option) Limiter {
+				return newAtomicInt64Based(rate, opts...)
+			},
+		},
 	}
 
 	for _, tt := range impls {
 		t.Run(tt.name, func(t *testing.T) {
+			// Set a non-default time.Time since some limiters (int64 in particular) use
+			// the default value as "non-initialized" state.
+			clockMock := clock.NewMock()
+			clockMock.Set(time.Now())
 			r := runnerImpl{
 				t:           t,
-				clock:       clock.NewMock(),
+				clock:       clockMock,
 				constructor: tt.constructor,
 				doneCh:      make(chan struct{}),
 			}

tools/go.mod

@@ -11,6 +11,7 @@ require (
 
 require (
 	github.com/BurntSushi/toml v1.0.0 // indirect
+	github.com/storozhukBM/benchart v1.0.0
 	golang.org/x/exp/typeparams v0.0.0-20220328175248-053ad81199eb // indirect
 	golang.org/x/mod v0.6.0-dev.0.20220106191415-9b9b3d81d5e3 // indirect
 	golang.org/x/sys v0.0.0-20220330033206-e17cdc41300f // indirect