internal/grpcrand: use Go top-level random functions for go1.21+

[kmirzavaziri]

This PR closes issue #6650.

What I did
I duplicated all functions in grpcrand package into another file, changing the implementation to call top-level functions of Go math/rand package internally, adding the _go1.21 suffix to new file name and build comments to both files, to instruct the Go compiler to compile the new file instead of the original one for Go 1.21 or higher.

Why
As described in the related issue, apart from reducing complexity, it is concurrent safe as of Go 1.21, and also significantly faster. I ran a benchmark to demonstrate the difference.

import (
	"math/rand"
	"sync"
	"testing"
	"time"
)

var (
	r  = rand.New(rand.NewSource(time.Now().UnixNano()))
	mu sync.Mutex
)

func BenchmarkIntMutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkIntTopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkInt63nMutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkInt63nTopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkIntnMutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkIntnTopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkInt31nMutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkInt31nTopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkFloat64Mutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkFloat64TopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkUint64Mutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkUint64TopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkUint32Mutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkUint32TopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkExpFloat64Mutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkExpFloat64TopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func BenchmarkShuffleMutex(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntMutex()
	}
}

func BenchmarkShuffleTopLevel(b *testing.B) {
	for i := 0; i < b.N; i++ {
		IntTopLevel()
	}
}

func IntMutex() int {
	mu.Lock()
	defer mu.Unlock()
	return r.Int()
}

func Int63nMutex(n int64) int64 {
	mu.Lock()
	defer mu.Unlock()
	return r.Int63n(n)
}

func IntnMutex(n int) int {
	mu.Lock()
	defer mu.Unlock()
	return r.Intn(n)
}

func Int31nMutex(n int32) int32 {
	mu.Lock()
	defer mu.Unlock()
	return r.Int31n(n)
}

func Float64Mutex() float64 {
	mu.Lock()
	defer mu.Unlock()
	return r.Float64()
}

func Uint64Mutex() uint64 {
	mu.Lock()
	defer mu.Unlock()
	return r.Uint64()
}

func Uint32Mutex() uint32 {
	mu.Lock()
	defer mu.Unlock()
	return r.Uint32()
}

func ExpFloat64Mutex() float64 {
	mu.Lock()
	defer mu.Unlock()
	return r.ExpFloat64()
}

func ShuffleMutex(n int, f func(int, int)) {
	mu.Lock()
	defer mu.Unlock()
	r.Shuffle(n, f)
}

func IntTopLevel() int {
	return r.Int()
}

func Int63nTopLevel(n int64) int64 {
	return rand.Int63n(n)
}

func IntnTopLevel(n int) int {
	return rand.Intn(n)
}

func Int31nTopLevel(n int32) int32 {
	return rand.Int31n(n)
}

func Float64TopLevel() float64 {
	return rand.Float64()
}

func Uint64TopLevel() uint64 {
	return rand.Uint64()
}

func Uint32TopLevel() uint32 {
	return rand.Uint32()
}

func ExpFloat64TopLevel() float64 {
	return rand.ExpFloat64()
}

func ShuffleTopLevel(n int, f func(int, int)) {
	rand.Shuffle(n, f)
}

results:

BenchmarkIntMutex-8                     86689021                13.69 ns/op
BenchmarkIntTopLevel-8                  464327850                2.581 ns/op
BenchmarkInt63nMutex-8                  87957193                13.74 ns/op
BenchmarkInt63nTopLevel-8               463219412                2.586 ns/op
BenchmarkIntnMutex-8                    87656822                13.71 ns/op
BenchmarkIntnTopLevel-8                 463425360                2.653 ns/op
BenchmarkInt31nMutex-8                  87715021                13.68 ns/op
BenchmarkInt31nTopLevel-8               464232123                2.577 ns/op
BenchmarkFloat64Mutex-8                 87786145                13.71 ns/op
BenchmarkFloat64TopLevel-8              463119002                2.583 ns/op
BenchmarkUint64Mutex-8                  87422935                13.73 ns/op
BenchmarkUint64TopLevel-8               462573543                2.605 ns/op
BenchmarkUint32Mutex-8                  87592838                13.80 ns/op
BenchmarkUint32TopLevel-8               461618060                2.607 ns/op
BenchmarkExpFloat64Mutex-8              87122502                15.18 ns/op
BenchmarkExpFloat64TopLevel-8           453928900                2.581 ns/op
BenchmarkShuffleMutex-8                 86752477                13.67 ns/op
BenchmarkShuffleTopLevel-8              465211470                2.585 ns/op

Making the functions ~5x faster.

RELEASE NOTES:

• rand: improve performance and simplify implementation of grpcrand by adopting math/rand's top-level functions for go version 1.21.0 and newer.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: kmirzavaziri / name: Kamyar Mirzavaziri (4c3353e)
• ✅ login: arvindbr8 / name: Arvind Bright (b7dc45f, f1811ed)

[codecov]

Codecov Report

Merging #6925 (f1811ed) into master (ddd377f) will increase coverage by 0.25%.
Report is 14 commits behind head on master.
The diff coverage is 77.77%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6925      +/-   ##
==========================================
+ Coverage   83.51%   83.76%   +0.25%     
==========================================
  Files         287      287              
  Lines       30920    30911       -9     
==========================================
+ Hits        25824    25894      +70     
+ Misses       4020     3957      -63     
+ Partials     1076     1060      -16     

Files	Coverage Δ
internal/grpcrand/grpcrand_go1.21.go	77.77% <77.77%> (ø)

... and 34 files with indirect coverage changes

[kmirzavaziri]

@dfawley, I would appreciate if you could take a look at this.

[arvindbr8]

LGTM. Thanks @kmirzavaziri

[dfawley]

Would you mind adding a TODO here that says something like:

"TODO: when this file is deleted (after Go 1.20 support is dropped), delete all of grpcrand and call the rand package directly."

?

[arvindbr8]

Done

[kmirzavaziri]

Sorry for my absence and thank you @arvindbr8

[arvindbr8]

No worries, sorry if you were working on the branch. Since this was a oneliner change, and since you had also allowed edits to your PR by maintainers I went ahead and made the change.

[dfawley]

We don't need both syntaxes for this, since we don't support Go 1.16 or earlier. Just //go:build is fine.

[arvindbr8]

Done

[dfawley]

ty @arvindbr8