[HAR-73] add a singleton package and tests in utils

need to return unique validator id for new nodes added into a shard

add a unit test of singleton package
test unique id generation, and non-unique id

Signed-off-by: Leo Chen <leo@harmony.one>

utils/singleton.go

@@ -0,0 +1,28 @@
+/* This module keeps all struct used as singleton */
+
+package utils
+
+import (
+	"sync"
+	"sync/atomic"
+)
+
+type UniqueValidatorId struct {
+	uniqueId uint32
+}
+
+var instance *UniqueValidatorId
+var once sync.Once
+
+func GetUniqueValidatorIdInstance() *UniqueValidatorId {
+	once.Do(func() {
+		instance = &UniqueValidatorId{
+			uniqueId: 0,
+		}
+	})
+	return instance
+}
+
+func (s *UniqueValidatorId) GetUniqueId() uint32 {
+	return atomic.AddUint32(&s.uniqueId, 1)
+}

utils/singleton_test.go

@@ -0,0 +1,41 @@
+package utils
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+var NumThreads int = 20
+
+func TestSingleton(t *testing.T) {
+	si := GetUniqueValidatorIdInstance()
+	var wg sync.WaitGroup
+
+	t.Log("unique ID provided by singleton instance")
+
+	for i := 0; i < NumThreads; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			t.Logf("id:%v\n", si.GetUniqueId())
+			time.Sleep(time.Millisecond)
+
+		}()
+	}
+	wg.Wait()
+
+	t.Log("non-unique ID")
+	n := 100
+	for i := 0; i < NumThreads; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			t.Log("num:", n)
+			n++
+			time.Sleep(time.Millisecond)
+		}()
+	}
+
+	wg.Wait()
+}