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math/rand/v2: remove Rand.Seed

Browse Source 
Removing Rand.Seed lets us remove lockedSource as well,
along with the ambiguity in globalRand about which source
to use.

For #61716.

Change-Id: Ibe150520dd1e7dd87165eacaebe9f0c2daeaedfd
Reviewed-on: https://go-review.googlesource.com/c/go/+/502498
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Rob Pike <r@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Russ Cox <rsc@golang.org>
This commit is contained in:
Russ Cox 2023-06-06 09:13:57 -04:00 committed by Gopher Robot
parent 48bd1fc93b
commit 1cc5b34d28
5 changed files with 25 additions and 315 deletions
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9
api/next/61716.txt
View File

@ -12,8 +12,6 @@ pkg math/rand/v2, func NewSource(int64) Source #61716
pkg math/rand/v2, func NewZipf(*Rand, float64, float64, uint64) *Zipf #61716
pkg math/rand/v2, func NormFloat64() float64 #61716
pkg math/rand/v2, func Perm(int) []int #61716
pkg math/rand/v2, func Seed //deprecated #61716
pkg math/rand/v2, func Seed(int64) #61716
pkg math/rand/v2, func Shuffle(int, func(int, int)) #61716
pkg math/rand/v2, func Uint32() uint32 #61716
pkg math/rand/v2, func Uint64() uint64 #61716
@ -28,17 +26,14 @@ pkg math/rand/v2, method (*Rand) Int64N(int64) int64 #61716
pkg math/rand/v2, method (*Rand) IntN(int) int #61716
pkg math/rand/v2, method (*Rand) NormFloat64() float64 #61716
pkg math/rand/v2, method (*Rand) Perm(int) []int #61716
pkg math/rand/v2, method (*Rand) Seed(int64) #61716
pkg math/rand/v2, method (*Rand) Shuffle(int, func(int, int)) #61716
pkg math/rand/v2, method (*Rand) Uint32() uint32 #61716
pkg math/rand/v2, method (*Rand) Uint64() uint64 #61716
pkg math/rand/v2, method (*Zipf) Uint64() uint64 #61716
pkg math/rand/v2, type Rand struct #61716
pkg math/rand/v2, type Source interface { Int64, Seed } #61716
pkg math/rand/v2, type Source interface { Int64 } #61716
pkg math/rand/v2, type Source interface, Int64() int64 #61716
pkg math/rand/v2, type Source interface, Seed(int64) #61716
pkg math/rand/v2, type Source64 interface { Int64, Seed, Uint64 } #61716
pkg math/rand/v2, type Source64 interface { Int64, Uint64 } #61716
pkg math/rand/v2, type Source64 interface, Int64() int64 #61716
pkg math/rand/v2, type Source64 interface, Seed(int64) #61716
pkg math/rand/v2, type Source64 interface, Uint64() uint64 #61716
pkg math/rand/v2, type Zipf struct #61716

8
src/math/rand/v2/auto_test.go
View File

@ -16,20 +16,20 @@ import (
func TestAuto(t *testing.T) {
// Pull out 10 int64s from the global source
// and then check that they don't appear in that
// order in the deterministic Seed(1) result.
// order in the deterministic seeded result.
var out []int64
for i := 0; i < 10; i++ {
out = append(out, Int64())
}
// Look for out in Seed(1)'s output.
// Look for out in seeded output.
// Strictly speaking, we should look for them in order,
// but this is good enough and not significantly more
// likely to have a false positive.
Seed(1)
r := New(NewSource(1))
found := 0
for i := 0; i < 1000; i++ {
x := Int64()
x := r.Int64()
if x == out[found] {
found++
if found == len(out) {

148
src/math/rand/v2/default_test.go
View File

@ -1,148 +0,0 @@
// Copyright 2023 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package rand_test
import (
"fmt"
"internal/race"
"internal/testenv"
. "math/rand/v2"
"os"
"runtime"
"strconv"
"sync"
"testing"
)
// Test that racy access to the default functions behaves reasonably.
func TestDefaultRace(t *testing.T) {
// Skip the test in short mode, but even in short mode run
// the test if we are using the race detector, because part
// of this is to see whether the race detector reports any problems.
if testing.Short() && !race.Enabled {
t.Skip("skipping starting another executable in short mode")
}
const env = "GO_RAND_TEST_HELPER_CODE"
if v := os.Getenv(env); v != "" {
doDefaultTest(t, v)
return
}
t.Parallel()
for i := 0; i < 6; i++ {
i := i
t.Run(strconv.Itoa(i), func(t *testing.T) {
t.Parallel()
exe, err := os.Executable()
if err != nil {
exe = os.Args[0]
}
cmd := testenv.Command(t, exe, "-test.run=TestDefaultRace")
cmd = testenv.CleanCmdEnv(cmd)
cmd.Env = append(cmd.Env, fmt.Sprintf("GO_RAND_TEST_HELPER_CODE=%d", i/2))
if i%2 != 0 {
cmd.Env = append(cmd.Env, "GODEBUG=randautoseed=0")
}
out, err := cmd.CombinedOutput()
if len(out) > 0 {
t.Logf("%s", out)
}
if err != nil {
t.Error(err)
}
})
}
}
// doDefaultTest should be run before there have been any calls to the
// top-level math/rand functions. Make sure that we can make concurrent
// calls to top-level functions and to Seed without any duplicate values.
// This will also give the race detector a change to report any problems.
func doDefaultTest(t *testing.T, v string) {
code, err := strconv.Atoi(v)
if err != nil {
t.Fatalf("internal error: unrecognized code %q", v)
}
goroutines := runtime.GOMAXPROCS(0)
if goroutines < 4 {
goroutines = 4
}
ch := make(chan uint64, goroutines*3)
var wg sync.WaitGroup
// The various tests below should not cause race detector reports
// and should not produce duplicate results.
//
// Note: these tests can theoretically fail when using fastrand64
// in that it is possible to coincidentally get the same random
// number twice. That could happen something like 1 / 2**64 times,
// which is rare enough that it may never happen. We don't worry
// about that case.
switch code {
case 0:
// Call Seed and Uint64 concurrently.
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func(s int64) {
defer wg.Done()
Seed(s)
}(int64(i) + 100)
}
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func() {
defer wg.Done()
ch <- Uint64()
}()
}
case 1:
// Call Uint64 concurrently with no Seed.
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func() {
defer wg.Done()
ch <- Uint64()
}()
}
case 2:
// Start with Uint64 to pick the fast source, then call
// Seed and Uint64 concurrently.
ch <- Uint64()
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func(s int64) {
defer wg.Done()
Seed(s)
}(int64(i) + 100)
}
wg.Add(goroutines)
for i := 0; i < goroutines; i++ {
go func() {
defer wg.Done()
ch <- Uint64()
}()
}
default:
t.Fatalf("internal error: unrecognized code %d", code)
}
go func() {
wg.Wait()
close(ch)
}()
m := make(map[uint64]bool)
for i := range ch {
if m[i] {
t.Errorf("saw %d twice", i)
}
m[i] = true
}
}

8
src/math/rand/v2/race_test.go
View File

@ -23,9 +23,8 @@ func TestConcurrent(t *testing.T) {
for i := 0; i < numRoutines; i++ {
go func(i int) {
defer wg.Done()
buf := make([]byte, 997)
var seed int64
for j := 0; j < numCycles; j++ {
var seed int64
seed += int64(ExpFloat64())
seed += int64(Float32())
seed += int64(Float64())
@ -38,11 +37,8 @@ func TestConcurrent(t *testing.T) {
for _, p := range Perm(10) {
seed += int64(p)
}
for _, b := range buf {
seed += int64(b)
}
Seed(int64(i*j) * seed)
}
_ = seed
}(i)
}
}

167
src/math/rand/v2/rand.go
View File

@ -18,9 +18,6 @@
package rand
import (
"internal/godebug"
"sync"
"sync/atomic"
_ "unsafe" // for go:linkname
)
@ -30,7 +27,6 @@ import (
// A Source is not safe for concurrent use by multiple goroutines.
type Source interface {
Int64() int64
Seed(seed int64)
}
// A Source64 is a Source that can also generate
@ -71,16 +67,6 @@ func New(src Source) *Rand {
return &Rand{src: src, s64: s64}
}
// Seed uses the provided seed value to initialize the generator to a deterministic state.
// Seed should not be called concurrently with any other Rand method.
func (r *Rand) Seed(seed int64) {
if lk, ok := r.src.(*lockedSource); ok {
lk.Seed(seed)
return
}
r.src.Seed(seed)
}
// Int64 returns a non-negative pseudo-random 63-bit integer as an int64.
func (r *Rand) Int64() int64 { return r.src.Int64() }
@ -259,46 +245,9 @@ func (r *Rand) Shuffle(n int, swap func(i, j int)) {
* Top-level convenience functions
*/
// globalRandGenerator is the source of random numbers for the top-level
// convenience functions. When possible it uses the runtime fastrand64
// function to avoid locking. This is not possible if the user called Seed,
// either explicitly or implicitly via GODEBUG=randautoseed=0.
var globalRandGenerator atomic.Pointer[Rand]
var randautoseed = godebug.New("randautoseed")
// globalRand returns the generator to use for the top-level convenience
// functions.
func globalRand() *Rand {
if r := globalRandGenerator.Load(); r != nil {
return r
}
// This is the first call. Initialize based on GODEBUG.
var r *Rand
if randautoseed.Value() == "0" {
randautoseed.IncNonDefault()
r = New(new(lockedSource))
r.Seed(1)
} else {
r = &Rand{
src: &fastSource{},
s64: &fastSource{},
}
}
if !globalRandGenerator.CompareAndSwap(nil, r) {
// Two different goroutines called some top-level
// function at the same time. While the results in
// that case are unpredictable, if we just use r here,
// and we are using a seed, we will most likely return
// the same value for both calls. That doesn't seem ideal.
// Just use the first one to get in.
return globalRandGenerator.Load()
}
return r
}
// globalRand is the source of random numbers for the top-level
// convenience functions.
var globalRand = &Rand{src: &fastSource{}}
//go:linkname fastrand64
func fastrand64() uint64
@ -310,107 +259,60 @@ func (*fastSource) Int64() int64 {
return int64(fastrand64() & rngMask)
}
func (*fastSource) Seed(int64) {
panic("internal error: call to fastSource.Seed")
}
func (*fastSource) Uint64() uint64 {
return fastrand64()
}
// Seed uses the provided seed value to initialize the default Source to a
// deterministic state. Seed values that have the same remainder when
// divided by 2³¹-1 generate the same pseudo-random sequence.
// Seed, unlike the Rand.Seed method, is safe for concurrent use.
//
// If Seed is not called, the generator is seeded randomly at program startup.
//
// Prior to Go 1.20, the generator was seeded like Seed(1) at program startup.
// To force the old behavior, call Seed(1) at program startup.
// Alternately, set GODEBUG=randautoseed=0 in the environment
// before making any calls to functions in this package.
//
// Deprecated: As of Go 1.20 there is no reason to call Seed with
// a random value. Programs that call Seed with a known value to get
// a specific sequence of results should use New(NewSource(seed)) to
// obtain a local random generator.
func Seed(seed int64) {
orig := globalRandGenerator.Load()
// If we are already using a lockedSource, we can just re-seed it.
if orig != nil {
if _, ok := orig.src.(*lockedSource); ok {
orig.Seed(seed)
return
}
}
// Otherwise either
// 1) orig == nil, which is the normal case when Seed is the first
// top-level function to be called, or
// 2) orig is already a fastSource, in which case we need to change
// to a lockedSource.
// Either way we do the same thing.
r := New(new(lockedSource))
r.Seed(seed)
if !globalRandGenerator.CompareAndSwap(orig, r) {
// Something changed underfoot. Retry to be safe.
Seed(seed)
}
}
// Int64 returns a non-negative pseudo-random 63-bit integer as an int64
// from the default Source.
func Int64() int64 { return globalRand().Int64() }
func Int64() int64 { return globalRand.Int64() }
// Uint32 returns a pseudo-random 32-bit value as a uint32
// from the default Source.
func Uint32() uint32 { return globalRand().Uint32() }
func Uint32() uint32 { return globalRand.Uint32() }
// Uint64 returns a pseudo-random 64-bit value as a uint64
// from the default Source.
func Uint64() uint64 { return globalRand().Uint64() }
func Uint64() uint64 { return globalRand.Uint64() }
// Int32 returns a non-negative pseudo-random 31-bit integer as an int32
// from the default Source.
func Int32() int32 { return globalRand().Int32() }
func Int32() int32 { return globalRand.Int32() }
// Int returns a non-negative pseudo-random int from the default Source.
func Int() int { return globalRand().Int() }
func Int() int { return globalRand.Int() }
// Int64N returns, as an int64, a non-negative pseudo-random number in the half-open interval [0,n)
// from the default Source.
// It panics if n <= 0.
func Int64N(n int64) int64 { return globalRand().Int64N(n) }
func Int64N(n int64) int64 { return globalRand.Int64N(n) }
// Int32N returns, as an int32, a non-negative pseudo-random number in the half-open interval [0,n)
// from the default Source.
// It panics if n <= 0.
func Int32N(n int32) int32 { return globalRand().Int32N(n) }
func Int32N(n int32) int32 { return globalRand.Int32N(n) }
// IntN returns, as an int, a non-negative pseudo-random number in the half-open interval [0,n)
// from the default Source.
// It panics if n <= 0.
func IntN(n int) int { return globalRand().IntN(n) }
func IntN(n int) int { return globalRand.IntN(n) }
// Float64 returns, as a float64, a pseudo-random number in the half-open interval [0.0,1.0)
// from the default Source.
func Float64() float64 { return globalRand().Float64() }
func Float64() float64 { return globalRand.Float64() }
// Float32 returns, as a float32, a pseudo-random number in the half-open interval [0.0,1.0)
// from the default Source.
func Float32() float32 { return globalRand().Float32() }
func Float32() float32 { return globalRand.Float32() }
// Perm returns, as a slice of n ints, a pseudo-random permutation of the integers
// in the half-open interval [0,n) from the default Source.
func Perm(n int) []int { return globalRand().Perm(n) }
func Perm(n int) []int { return globalRand.Perm(n) }
// Shuffle pseudo-randomizes the order of elements using the default Source.
// n is the number of elements. Shuffle panics if n < 0.
// swap swaps the elements with indexes i and j.
func Shuffle(n int, swap func(i, j int)) { globalRand().Shuffle(n, swap) }
func Shuffle(n int, swap func(i, j int)) { globalRand.Shuffle(n, swap) }
// NormFloat64 returns a normally distributed float64 in the range
// [-math.MaxFloat64, +math.MaxFloat64] with
@ -420,7 +322,7 @@ func Shuffle(n int, swap func(i, j int)) { globalRand().Shuffle(n, swap) }
// adjust the output using:
//
// sample = NormFloat64() * desiredStdDev + desiredMean
func NormFloat64() float64 { return globalRand().NormFloat64() }
func NormFloat64() float64 { return globalRand.NormFloat64() }
// ExpFloat64 returns an exponentially distributed float64 in the range
// (0, +math.MaxFloat64] with an exponential distribution whose rate parameter
@ -429,39 +331,4 @@ func NormFloat64() float64 { return globalRand().NormFloat64() }
// callers can adjust the output using:
//
// sample = ExpFloat64() / desiredRateParameter
func ExpFloat64() float64 { return globalRand().ExpFloat64() }
type lockedSource struct {
lk sync.Mutex
s *rngSource
}
func (r *lockedSource) Int64() (n int64) {
r.lk.Lock()
n = r.s.Int64()
r.lk.Unlock()
return
}
func (r *lockedSource) Uint64() (n uint64) {
r.lk.Lock()
n = r.s.Uint64()
r.lk.Unlock()
return
}
func (r *lockedSource) Seed(seed int64) {
r.lk.Lock()
r.seed(seed)
r.lk.Unlock()
}
// seed seeds the underlying source.
// The caller must have locked r.lk.
func (r *lockedSource) seed(seed int64) {
if r.s == nil {
r.s = newSource(seed)
} else {
r.s.Seed(seed)
}
}
func ExpFloat64() float64 { return globalRand.ExpFloat64() }