avoid multiple initialization of rand (#183)

* avoid multiple initialization of rand

* fix my mistake of resolving the conflict

Co-authored-by: Bhautik Pipaliya <56270044+bhautikpip@users.noreply.github.com>

utils/rand.go

@@ -9,12 +9,72 @@
 package utils
 
 import (
+	crand "crypto/rand"
+	"encoding/binary"
 	"math/rand"
+	"sync"
 	"time"
 )
 
-func init() {
-	rand.Seed(time.Now().UnixNano())
+// check lockedSource implements rand.Source
+var _ rand.Source = (*lockedSource)(nil)
+var _ rand.Source64 = (*lockedSource64)(nil)
+
+type lockedSource struct {
+	mu  sync.Mutex
+	src rand.Source
+}
+
+func (src *lockedSource) Int63() int64 {
+	src.mu.Lock()
+	defer src.mu.Unlock()
+	return src.src.Int63()
+}
+
+func (src *lockedSource) Seed(seed int64) {
+	src.mu.Lock()
+	defer src.mu.Unlock()
+	src.src.Seed(seed)
+}
+
+type lockedSource64 struct {
+	mu  sync.Mutex
+	src rand.Source64
+}
+
+func (src *lockedSource64) Int63() int64 {
+	src.mu.Lock()
+	defer src.mu.Unlock()
+	return src.src.Int63()
+}
+
+func (src *lockedSource64) Uint64() uint64 {
+	src.mu.Lock()
+	defer src.mu.Unlock()
+	return src.src.Uint64()
+}
+
+func (src *lockedSource64) Seed(seed int64) {
+	src.mu.Lock()
+	defer src.mu.Unlock()
+	src.src.Seed(seed)
+}
+
+func newSeed() int64 {
+	var seed int64
+	if err := binary.Read(crand.Reader, binary.BigEndian, &seed); err != nil {
+		// fallback to timestamp
+		seed = time.Now().UnixNano()
+	}
+	return seed
+}
+
+func newGlobalRand() *rand.Rand {
+	src := rand.NewSource(newSeed())
+	if src64, ok := src.(rand.Source64); ok {
+		return rand.New(&lockedSource64{src: src64})
+	}
+	return rand.New(&lockedSource{src: src})
 }
 
 // Rand is an interface for a set of methods that return random value.
@@ -25,22 +85,25 @@ type Rand interface {
 }
 
 // DefaultRand is an implementation of Rand interface.
+// It is safe for concurrent use by multiple goroutines.
 type DefaultRand struct{}
 
+var globalRand = newGlobalRand()
+
 // Int63n returns, as an int64, a non-negative pseudo-random number in [0,n)
 // from the default Source.
 func (r *DefaultRand) Int63n(n int64) int64 {
-	return rand.Int63n(n)
+	return globalRand.Int63n(n)
 }
 
 // Intn returns, as an int, a non-negative pseudo-random number in [0,n)
 // from the default Source.
 func (r *DefaultRand) Intn(n int) int {
-	return rand.Intn(n)
+	return globalRand.Intn(n)
 }
 
 // Float64 returns, as a float64, a pseudo-random number in [0.0,1.0)
 // from the default Source.
 func (r *DefaultRand) Float64() float64 {
-	return rand.Float64()
+	return globalRand.Float64()
 }

utils/timer.go

@@ -9,14 +9,9 @@
 package utils
 
 import (
-	"math/rand"
 	"time"
 )
 
-func init() {
-	rand.Seed(time.Now().UnixNano())
-}
-
 // Timer is the same as time.Timer except that it has jitters.
 // A Timer must be created with NewTimer.
 type Timer struct {
@@ -27,7 +22,7 @@ type Timer struct {
 
 // NewTimer creates a new Timer that will send the current time on its channel.
 func NewTimer(d, jitter time.Duration) *Timer {
-	t := time.NewTimer(d - time.Duration(rand.Int63n(int64(jitter))))
+	t := time.NewTimer(d - time.Duration(globalRand.Int63n(int64(jitter))))
 
 	jitteredTimer := Timer{
 		t:      t,
@@ -46,5 +41,5 @@ func (j *Timer) C() <-chan time.Time {
 // Reset resets the timer.
 // Reset should be invoked only on stopped or expired timers with drained channels.
 func (j *Timer) Reset() {
-	j.t.Reset(j.d - time.Duration(rand.Int63n(int64(j.jitter))))
+	j.t.Reset(j.d - time.Duration(globalRand.Int63n(int64(j.jitter))))
 }