Use of runtime.Mid and runtime.Fastrand

rand_test.go

package benchmarks

/*
BenchmarkRandInt63_Global-4                     10000000               154 ns/op
BenchmarkRandInt63_Channel-4                    10000000               220 ns/op
BenchmarkRandInt63_Pool-4                       50000000                28.8 ns/op
BenchmarkSourceInt63_Pool-4                     50000000                34.9 ns/op
BenchmarkRandInt63_Source-4                     300000000                5.71 ns/op
BenchmarkRandInt63_ShardsGettid-4               50000000                29.2 ns/op
BenchmarkRandInt63_ShardsMid-4                  100000000               14.2 ns/op
BenchmarkRandInt63_ShardsFastrand-4             30000000                49.0 ns/op
BenchmarkRandInt63_ShardsMidFastrand-4          100000000               17.1 ns/op
*/

import (
	"math/rand"
	"runtime"
	"sync"
	"syscall"
	"testing"
)

// START_GLOBAL OMIT
func BenchmarkRandInt63_Global(b *testing.B) {
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			rand.Int63() // HL
		}
	})
}

// END_GLOBAL OMIT

// START_CHANNEL OMIT
func BenchmarkRandInt63_Channel(b *testing.B) {
	ch := make(chan int64, 1000) // HL
	go func() {
		r := rand.New(rand.NewSource(rand.Int63())) // HL
		for {
			ch <- r.Int63() // HL
		}
	}()

	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			_ = <-ch // HL
		}
	})
}

// END_CHANNEL OMIT

// START_POOL OMIT

func BenchmarkRandInt63_Pool(b *testing.B) {
	var pool = sync.Pool{ // HL
		New: func() interface{} { // HL
			return rand.New(rand.NewSource(rand.Int63())) // HL
		}, // HL
	} // HL

	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			r := pool.Get().(*rand.Rand) // HL
			r.Int63()
			pool.Put(r) // HL
		}
	})
}

func BenchmarkSourceInt63_Pool(b *testing.B) {
	var pool = sync.Pool{ // HL
		New: func() interface{} { // HL
			return rand.NewSource(rand.Int63()) // HL
		}, // HL
	} // HL

	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			r := pool.Get().(rand.Source) // HL
			r.Int63()
			pool.Put(r) // HL
		}
	})
}

// END_POOL OMIT

// START_SOURCE OMIT
func BenchmarkRandInt63_Source(b *testing.B) {
	b.RunParallel(func(pb *testing.PB) {
		r := rand.New(rand.NewSource(rand.Int63())) // HL
		for pb.Next() {
			r.Int63()
		}
	})
}

// END_SOURCE OMIT

func BenchmarkRandInt63_ShardsGettid(b *testing.B) {
	rands := make([]*rand.Rand, 32)
	for i := range rands {
		rands[i] = rand.New(rand.NewSource(rand.Int63()))
	}
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			rands[syscall.Gettid()&31].Int63()
		}
	})
}

type shard struct {
	r *rand.Rand
	m sync.Mutex
}

func (sh *shard) Int63() (f int64) {
	sh.m.Lock()
	f = sh.r.Int63()
	sh.m.Unlock()
	return
}

const ShardsPerMid = 8

func newShards() (shards []shard) {
	shards = make([]shard, runtime.GOMAXPROCS(-1)*ShardsPerMid)
	for i := range shards {
		shards[i].r = rand.New(rand.NewSource(rand.Int63()))
	}
	return
}

func BenchmarkRandInt63_ShardsMid(b *testing.B) {
	shards := newShards()
	l := uint32(len(shards) - 1)
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			shards[(runtime.Mid()*ShardsPerMid)&l].Int63()
		}
	})
}

func BenchmarkRandInt63_ShardsFastrand(b *testing.B) {
	shards := newShards()
	l := uint32(len(shards) - 1)
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			shards[runtime.Fastrand()&l].Int63()
		}
	})
}

func BenchmarkRandInt63_ShardsMidFastrand(b *testing.B) {
	shards := newShards()
	l := uint32(len(shards) - 1)
	b.RunParallel(func(pb *testing.PB) {
		for pb.Next() {
			shards[(runtime.Mid()*ShardsPerMid+runtime.Fastrand()&(ShardsPerMid-1))&l].Int63()
		}
	})
}