Migrate code

Author: willzhen

Diff for: go.mod

@@ -0,0 +1,7 @@
+module github.com/memory-overflow/go-orderedmap
+
+go 1.16
+
+require (
+	github.com/json-iterator/go v1.1.12
+)

Diff for: limit_waitgroup.go

@@ -0,0 +1,36 @@
+package stlextension
+
+import "sync"
+
+// LimitWaitGroup ...
+type LimitWaitGroup struct {
+	wg     sync.WaitGroup
+	bucket chan struct{}
+}
+
+// NewLimitWaitGroup ...
+func NewLimitWaitGroup(limit uint) *LimitWaitGroup {
+	return &LimitWaitGroup{
+		wg:     sync.WaitGroup{},
+		bucket: make(chan struct{}, limit),
+	}
+}
+
+// Add ...
+func (w *LimitWaitGroup) Add(delta int) {
+	w.wg.Add(delta)
+	for i := 0; i < delta; i++ {
+		w.bucket <- struct{}{}
+	}
+}
+
+// Done ...
+func (w *LimitWaitGroup) Done() {
+	<-w.bucket
+	w.wg.Done()
+}
+
+// Wait ...
+func (w *LimitWaitGroup) Wait() {
+	w.wg.Wait()
+}