all: replace math/rand with math/rand/v2 (#6732)

Update to new stdlib apis.

The new Float64 is uniform, which resolves a long comment.


https://cs.opensource.google/go/go/+/refs/tags/go1.24.2:src/math/rand/v2/rand.go;l=209

> // There are exactly 1<<53 float64s in [0,1). Use Intn(1<<53) /
(1<<53).
	return float64(r.Uint64()<<11>>11) / (1 << 53)

```
goos: linux
goarch: amd64
pkg: go.opentelemetry.io/otel/sdk/trace
cpu: 12th Gen Intel(R) Core(TM) i7-1260P
                                 │   old.txt    │               new.txt                │
                                 │    sec/op    │    sec/op     vs base                │
TraceStart/with_a_simple_span-16   387.1n ±  5%   306.8n ± 15%  -20.73% (p=0.000 n=10)
TraceStart/with_several_links-16   542.2n ±  5%   501.0n ±  2%   -7.61% (p=0.000 n=10)
TraceStart/with_attributes-16      521.4n ± 14%   571.6n ±  6%   +9.64% (p=0.009 n=10)
geomean                            478.3n         444.6n         -7.05%

                                 │  old.txt   │               new.txt               │
                                 │    B/op    │    B/op     vs base                 │
TraceStart/with_a_simple_span-16   528.0 ± 0%   528.0 ± 0%       ~ (p=1.000 n=10) ¹
TraceStart/with_several_links-16   704.0 ± 0%   704.0 ± 0%       ~ (p=1.000 n=10) ¹
TraceStart/with_attributes-16      784.0 ± 0%   784.0 ± 0%       ~ (p=1.000 n=10) ¹
geomean                            663.0        663.0       +0.00%
¹ all samples are equal

                                 │  old.txt   │               new.txt               │
                                 │ allocs/op  │ allocs/op   vs base                 │
TraceStart/with_a_simple_span-16   2.000 ± 0%   2.000 ± 0%       ~ (p=1.000 n=10) ¹
TraceStart/with_several_links-16   3.000 ± 0%   3.000 ± 0%       ~ (p=1.000 n=10) ¹
TraceStart/with_attributes-16      4.000 ± 0%   4.000 ± 0%       ~ (p=1.000 n=10) ¹
geomean                            2.884        2.884       +0.00%
¹ all samples are equal
```

---------

Co-authored-by: Robert Pająk <[email protected]>
Co-authored-by: Damien Mathieu <[email protected]>

Author: 3 people

baggage/baggage_test.go

@@ -5,7 +5,7 @@ package baggage
 
 import (
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"slices"
 	"strings"
 	"testing"
@@ -17,12 +17,8 @@ import (
 	"go.opentelemetry.io/otel/internal/baggage"
 )
 
-var rng *rand.Rand
-
-func init() {
-	// Seed with a static value to ensure deterministic results.
-	rng = rand.New(rand.NewSource(1))
-}
+// Seed with a static value to ensure deterministic results.
+var rng = rand.New(rand.NewChaCha8([32]byte{}))
 
 func TestValidateKeyChar(t *testing.T) {
 	// ASCII only
@@ -255,7 +251,7 @@ func key(n int) string {
 
 	b := make([]rune, n)
 	for i := range b {
-		b[i] = r[rng.Intn(len(r))]
+		b[i] = r[rng.IntN(len(r))]
 	}
 	return string(b)
 }

bridge/opencensus/internal/ocmetric/metric_test.go

@@ -7,7 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"math"
-	"math/rand"
+	"math/rand/v2"
 	"reflect"
 	"strconv"
 	"testing"
@@ -1189,7 +1189,7 @@ func BenchmarkConvertExemplar(b *testing.B) {
 	for i := range data {
 		a := make(ocmetricdata.Attachments, attchmentsN)
 		for j := 0; j < attchmentsN; j++ {
-			a[strconv.Itoa(j)] = rand.Int63()
+			a[strconv.Itoa(j)] = rand.Int64()
 		}
 		data[i] = &ocmetricdata.Exemplar{
 			Value:       rand.NormFloat64(),

bridge/opentracing/internal/mock.go

@@ -5,7 +5,7 @@ package internal // import "go.opentelemetry.io/otel/bridge/opentracing/internal
 
 import (
 	"context"
-	"math/rand"
+	"math/rand/v2"
 	"reflect"
 	"sync"
 	"time"
@@ -44,7 +44,7 @@ type MockTracer struct {
 	TraceFlags            trace.TraceFlags
 
 	randLock sync.Mutex
-	rand     *rand.Rand
+	rand     *rand.ChaCha8
 }
 
 var (
@@ -53,13 +53,15 @@ var (
 )
 
 func NewMockTracer() *MockTracer {
+	u := rand.Uint32()
+	seed := [32]byte{byte(u), byte(u >> 8), byte(u >> 16), byte(u >> 24)}
 	return &MockTracer{
 		FinishedSpans:         nil,
 		SpareTraceIDs:         nil,
 		SpareSpanIDs:          nil,
 		SpareContextKeyValues: nil,
 
-		rand: rand.New(rand.NewSource(time.Now().Unix())),
+		rand: rand.NewChaCha8(seed),
 	}
 }
 

metric/example_test.go

@@ -7,7 +7,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"net/http"
 	"runtime"
 	"time"
@@ -159,7 +159,7 @@ func ExampleMeter_gauge() {
 	getCPUFanSpeed := func() int64 {
 		// Generates a random fan speed for demonstration purpose.
 		// In real world applications, replace this to get the actual fan speed.
-		return int64(1500 + rand.Intn(1000))
+		return int64(1500 + rand.IntN(1000))
 	}
 
 	fanSpeedSubscription := make(chan int64, 1)
@@ -170,7 +170,7 @@ func ExampleMeter_gauge() {
 			// Synchronous gauges are used when the measurement cycle is
 			// synchronous to an external change.
 			// Simulate that external cycle here.
-			time.Sleep(time.Duration(rand.Intn(3)) * time.Second)
+			time.Sleep(time.Duration(rand.IntN(3)) * time.Second)
 			fanSpeed := getCPUFanSpeed()
 			fanSpeedSubscription <- fanSpeed
 		}

sdk/metric/exemplar/fixed_size_reservoir.go

@@ -6,7 +6,7 @@ package exemplar // import "go.opentelemetry.io/otel/sdk/metric/exemplar"
 import (
 	"context"
 	"math"
-	"math/rand"
+	"math/rand/v2"
 	"time"
 
 	"go.opentelemetry.io/otel/attribute"
@@ -44,18 +44,11 @@ type FixedSizeReservoir struct {
 	// w is the largest random number in a distribution that is used to compute
 	// the next next.
 	w float64
-
-	// rng is used to make sampling decisions.
-	//
-	// Do not use crypto/rand. There is no reason for the decrease in performance
-	// given this is not a security sensitive decision.
-	rng *rand.Rand
 }
 
 func newFixedSizeReservoir(s *storage) *FixedSizeReservoir {
 	r := &FixedSizeReservoir{
 		storage: s,
-		rng:     rand.New(rand.NewSource(time.Now().UnixNano())),
 	}
 	r.reset()
 	return r
@@ -64,26 +57,15 @@ func newFixedSizeReservoir(s *storage) *FixedSizeReservoir {
 // randomFloat64 returns, as a float64, a uniform pseudo-random number in the
 // open interval (0.0,1.0).
 func (r *FixedSizeReservoir) randomFloat64() float64 {
-	// TODO: This does not return a uniform number. rng.Float64 returns a
-	// uniformly random int in [0,2^53) that is divided by 2^53. Meaning it
-	// returns multiples of 2^-53, and not all floating point numbers between 0
-	// and 1 (i.e. for values less than 2^-4 the 4 last bits of the significand
-	// are always going to be 0).
-	//
-	// An alternative algorithm should be considered that will actually return
-	// a uniform number in the interval (0,1). For example, since the default
-	// rand source provides a uniform distribution for Int63, this can be
-	// converted following the prototypical code of Mersenne Twister 64 (Takuji
-	// Nishimura and Makoto Matsumoto:
-	// http://www.math.sci.hiroshima-u.ac.jp/m-mat/MT/VERSIONS/C-LANG/mt19937-64.c)
+	// TODO: Use an algorithm that avoids rejection sampling. For example:
 	//
-	//   (float64(rng.Int63()>>11) + 0.5) * (1.0 / 4503599627370496.0)
-	//
-	// There are likely many other methods to explore here as well.
-
-	f := r.rng.Float64()
+	//   const precision = 1 << 53 // 2^53
+	//   // Generate an integer in [1, 2^53 - 1]
+	//   v := rand.Uint64() % (precision - 1) + 1
+	//   return float64(v) / float64(precision)
+	f := rand.Float64()
 	for f == 0 {
-		f = r.rng.Float64()
+		f = rand.Float64()
 	}
 	return f
 }
@@ -146,7 +128,7 @@ func (r *FixedSizeReservoir) Offer(ctx context.Context, t time.Time, n Value, a
 	} else {
 		if r.count == r.next {
 			// Overwrite a random existing measurement with the one offered.
-			idx := int(r.rng.Int63n(int64(cap(r.store))))
+			idx := int(rand.Int64N(int64(cap(r.store))))
 			r.store[idx] = newMeasurement(ctx, t, n, a)
 			r.advance()
 		}

sdk/metric/exemplar/fixed_size_reservoir_test.go

@@ -6,10 +6,9 @@ package exemplar
 import (
 	"context"
 	"math"
-	"math/rand"
+	"math/rand/v2"
 	"slices"
 	"testing"
-	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -28,7 +27,10 @@ func TestNewFixedSizeReservoirSamplingCorrectness(t *testing.T) {
 	intensity := 0.1
 	sampleSize := 1000
 
-	rng := rand.New(rand.NewSource(time.Now().UnixNano()))
+	u := rand.Uint32()
+	seed := [32]byte{byte(u), byte(u >> 8), byte(u >> 16), byte(u >> 24)}
+	t.Logf("rng seed: %x", seed)
+	rng := rand.New(rand.NewChaCha8(seed))
 
 	data := make([]float64, sampleSize*1000)
 	for i := range data {

sdk/resource/benchmark_test.go

@@ -5,7 +5,7 @@ package resource_test
 
 import (
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"testing"
 
 	"go.opentelemetry.io/otel/attribute"
@@ -21,18 +21,18 @@ func makeAttrs(n int) (_, _ *resource.Resource) {
 	for i := 0; i < n; i++ {
 		var k string
 		for {
-			k = fmt.Sprint("k", rand.Intn(1000000000))
+			k = fmt.Sprint("k", rand.IntN(1000000000))
 			if !used[k] {
 				used[k] = true
 				break
 			}
 		}
-		l1[i] = attribute.String(k, fmt.Sprint("v", rand.Intn(1000000000)))
+		l1[i] = attribute.String(k, fmt.Sprint("v", rand.IntN(1000000000)))
 
 		if rand.Float64() < conflict {
 			l2[i] = l1[i]
 		} else {
-			l2[i] = attribute.String(k, fmt.Sprint("v", rand.Intn(1000000000)))
+			l2[i] = attribute.String(k, fmt.Sprint("v", rand.IntN(1000000000)))
 		}
 	}
 	return resource.NewSchemaless(l1...), resource.NewSchemaless(l2...)

sdk/trace/id_generator.go

@@ -5,10 +5,8 @@ package trace // import "go.opentelemetry.io/otel/sdk/trace"
 
 import (
 	"context"
-	crand "crypto/rand"
 	"encoding/binary"
-	"math/rand"
-	"sync"
+	"math/rand/v2"
 
 	"go.opentelemetry.io/otel/trace"
 )
@@ -29,20 +27,15 @@ type IDGenerator interface {
 	// must never be done outside of a new major release.
 }
 
-type randomIDGenerator struct {
-	sync.Mutex
-	randSource *rand.Rand
-}
+type randomIDGenerator struct{}
 
 var _ IDGenerator = &randomIDGenerator{}
 
 // NewSpanID returns a non-zero span ID from a randomly-chosen sequence.
 func (gen *randomIDGenerator) NewSpanID(ctx context.Context, traceID trace.TraceID) trace.SpanID {
-	gen.Lock()
-	defer gen.Unlock()
 	sid := trace.SpanID{}
 	for {
-		_, _ = gen.randSource.Read(sid[:])
+		binary.NativeEndian.PutUint64(sid[:], rand.Uint64())
 		if sid.IsValid() {
 			break
 		}
@@ -53,18 +46,17 @@ func (gen *randomIDGenerator) NewSpanID(ctx context.Context, traceID trace.Trace
 // NewIDs returns a non-zero trace ID and a non-zero span ID from a
 // randomly-chosen sequence.
 func (gen *randomIDGenerator) NewIDs(ctx context.Context) (trace.TraceID, trace.SpanID) {
-	gen.Lock()
-	defer gen.Unlock()
 	tid := trace.TraceID{}
 	sid := trace.SpanID{}
 	for {
-		_, _ = gen.randSource.Read(tid[:])
+		binary.NativeEndian.PutUint64(tid[:8], rand.Uint64())
+		binary.NativeEndian.PutUint64(tid[8:], rand.Uint64())
 		if tid.IsValid() {
 			break
 		}
 	}
 	for {
-		_, _ = gen.randSource.Read(sid[:])
+		binary.NativeEndian.PutUint64(sid[:], rand.Uint64())
 		if sid.IsValid() {
 			break
 		}
@@ -73,9 +65,5 @@ func (gen *randomIDGenerator) NewIDs(ctx context.Context) (trace.TraceID, trace.
 }
 
 func defaultIDGenerator() IDGenerator {
-	gen := &randomIDGenerator{}
-	var rngSeed int64
-	_ = binary.Read(crand.Reader, binary.LittleEndian, &rngSeed)
-	gen.randSource = rand.New(rand.NewSource(rngSeed))
-	return gen
+	return &randomIDGenerator{}
 }

sdk/trace/provider_test.go

@@ -7,7 +7,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"testing"
 
 	"github.com/stretchr/testify/assert"

sdk/trace/sampling_test.go

@@ -6,7 +6,7 @@ package trace
 import (
 	"context"
 	"fmt"
-	"math/rand"
+	"math/rand/v2"
 	"testing"
 
 	"github.com/stretchr/testify/assert"