Update to avoid pseudo-random number (#5225)

* Update to avoid pseudo-random number

This PR update the usage of rand so that non-global seed is used.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

* Add concurrency-safe random source

See https://stackoverflow.com/questions/48958886/how-to-create-a-thread-safe-rand-source

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

plugin/pkg/rand/rand.go

@@ -0,0 +1,36 @@
+// Package rand is used for concurrency safe random number generator.
+package rand
+
+import (
+	"math/rand"
+	"sync"
+)
+
+// Rand is used for concurrency safe random number generator.
+type Rand struct {
+	m sync.Mutex
+	r *rand.Rand
+}
+
+// New returns a new Rand from seed.
+func New(seed int64) *Rand {
+	return &Rand{r: rand.New(rand.NewSource(seed))}
+}
+
+// Int returns a non-negative pseudo-random int from the Source in Rand.r.
+func (r *Rand) Int() int {
+	r.m.Lock()
+	v := r.r.Int()
+	r.m.Unlock()
+	return v
+}
+
+// Perm returns, as a slice of n ints, a pseudo-random permutation of the
+// integers in the half-open interval [0,n) from the Source in Rand.r.
+func (r *Rand) Perm(n int) []int {
+	r.m.Lock()
+	v := r.r.Perm(n)
+	r.m.Unlock()
+	return v
+
+}